comparison modules/field/field.api.php @ 0:ff03f76ab3fe

initial version

+<?php
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Exposes "pseudo-field" components on fieldable entities.
+ *
+ * Field UI's "Manage fields" and "Manage display" pages let users re-order
+ * fields, but also non-field components. For nodes, these include the title,
+ * poll choices, and other elements exposed by modules through hook_form() or
+ * hook_form_alter().
+ *
+ * Fieldable entities or modules that want to have their components supported
+ * should expose them using this hook. The user-defined settings (weight,
+ * visible) are automatically applied on rendered forms and displayed
+ * entities in a #pre_render callback added by field_attach_form() and
+ * field_attach_view().
+ *
+ * @see _field_extra_fields_pre_render()
+ * @see hook_field_extra_fields_alter()
+ *
+ * @return
+ *   A nested array of 'pseudo-field' elements. Each list is nested within the
+ *   following keys: entity type, bundle name, context (either 'form' or
+ *   'display'). The keys are the name of the elements as appearing in the
+ *   renderable array (either the entity form or the displayed entity). The
+ *   value is an associative array:
+ *   - label: The human readable name of the element.
+ *   - description: A short description of the element contents.
+ *   - weight: The default weight of the element.
+ *   - edit: (optional) String containing markup (normally a link) used as the
+ *     element's 'edit' operation in the administration interface. Only for
+ *     'form' context.
+ *   - delete: (optional) String containing markup (normally a link) used as the
+ *     element's 'delete' operation in the administration interface. Only for
+ *     'form' context.
+ */
+function hook_field_extra_fields() {
+  $extra['node']['poll'] = array(
+    'form' => array(
+      'choice_wrapper' => array(
+        'label' => t('Poll choices'),
+        'description' => t('Poll choices'),
+        'weight' => -4,
+      ),
+      'settings' => array(
+        'label' => t('Poll settings'),
+        'description' => t('Poll module settings'),
+        'weight' => -3,
+      ),
+    ),
+    'display' => array(
+      'poll_view_voting' => array(
+        'label' => t('Poll vote'),
+        'description' => t('Poll vote'),
+        'weight' => 0,
+      ),
+      'poll_view_results' => array(
+        'label' => t('Poll results'),
+        'description' => t('Poll results'),
+        'weight' => 0,
+      ),
+    )
+  );
+
+  return $extra;
+}
+
+/**
+ * Alter "pseudo-field" components on fieldable entities.
+ *
+ * @param $info
+ *   The associative array of 'pseudo-field' components.
+ *
+ * @see hook_field_extra_fields()
+ */
+function hook_field_extra_fields_alter(&$info) {
+  // Force node title to always be at the top of the list by default.
+  foreach (node_type_get_types() as $bundle) {
+    if (isset($info['node'][$bundle->type]['form']['title'])) {
+      $info['node'][$bundle->type]['form']['title']['weight'] = -20;
+    }
+  }
+}
+
+/**
+ * @defgroup field_types Field Types API
+ * @{
+ * Define field types.
+ *
+ * In the Field API, each field has a type, which determines what kind of data
+ * (integer, string, date, etc.) the field can hold, which settings it provides,
+ * and so on. The data type(s) accepted by a field are defined in
+ * hook_field_schema(); other basic properties of a field are defined in
+ * hook_field_info(). The other hooks below are called by the Field Attach API
+ * to perform field-type-specific actions.
+ *
+ * The Field Types API also defines two kinds of pluggable handlers: widgets
+ * and formatters. @link field_widget Widgets @endlink specify how the field
+ * appears in edit forms, while @link field_formatter formatters @endlink
+ * specify how the field appears in displayed entities.
+ *
+ * A third kind of pluggable handlers, storage backends, is defined by the
+ * @link field_storage Field Storage API @endlink.
+ *
+ * See @link field Field API @endlink for information about the other parts of
+ * the Field API.
+ */
+
+/**
+ * Define Field API field types.
+ *
+ * @return
+ *   An array whose keys are field type names and whose values are arrays
+ *   describing the field type, with the following key/value pairs:
+ *   - label: The human-readable name of the field type.
+ *   - description: A short description for the field type.
+ *   - settings: An array whose keys are the names of the settings available
+ *     for the field type, and whose values are the default values for those
+ *     settings.
+ *   - instance_settings: An array whose keys are the names of the settings
+ *     available for instances of the field type, and whose values are the
+ *     default values for those settings. Instance-level settings can have
+ *     different values on each field instance, and thus allow greater
+ *     flexibility than field-level settings. It is recommended to put settings
+ *     at the instance level whenever possible. Notable exceptions: settings
+ *     acting on the schema definition, or settings that Views needs to use
+ *     across field instances (for example, the list of allowed values).
+ *   - default_widget: The machine name of the default widget to be used by
+ *     instances of this field type, when no widget is specified in the
+ *     instance definition. This widget must be available whenever the field
+ *     type is available (i.e. provided by the field type module, or by a module
+ *     the field type module depends on).
+ *   - default_formatter: The machine name of the default formatter to be used
+ *     by instances of this field type, when no formatter is specified in the
+ *     instance definition. This formatter must be available whenever the field
+ *     type is available (i.e. provided by the field type module, or by a module
+ *     the field type module depends on).
+ *   - no_ui: (optional) A boolean specifying that users should not be allowed
+ *     to create fields and instances of this field type through the UI. Such
+ *     fields can only be created programmatically with field_create_field()
+ *     and field_create_instance(). Defaults to FALSE.
+ *
+ * @see hook_field_info_alter()
+ */
+function hook_field_info() {
+  return array(
+    'text' => array(
+      'label' => t('Text'),
+      'description' => t('This field stores varchar text in the database.'),
+      'settings' => array('max_length' => 255),
+      'instance_settings' => array('text_processing' => 0),
+      'default_widget' => 'text_textfield',
+      'default_formatter' => 'text_default',
+    ),
+    'text_long' => array(
+      'label' => t('Long text'),
+      'description' => t('This field stores long text in the database.'),
+      'settings' => array('max_length' => ''),
+      'instance_settings' => array('text_processing' => 0),
+      'default_widget' => 'text_textarea',
+      'default_formatter' => 'text_default',
+    ),
+    'text_with_summary' => array(
+      'label' => t('Long text and summary'),
+      'description' => t('This field stores long text in the database along with optional summary text.'),
+      'settings' => array('max_length' => ''),
+      'instance_settings' => array('text_processing' => 1, 'display_summary' => 0),
+      'default_widget' => 'text_textarea_with_summary',
+      'default_formatter' => 'text_summary_or_trimmed',
+    ),
+  );
+}
+
+/**
+ * Perform alterations on Field API field types.
+ *
+ * @param $info
+ *   Array of information on field types exposed by hook_field_info()
+ *   implementations.
+ */
+function hook_field_info_alter(&$info) {
+  // Add a setting to all field types.
+  foreach ($info as $field_type => $field_type_info) {
+    $info[$field_type]['settings'] += array(
+      'mymodule_additional_setting' => 'default value',
+    );
+  }
+
+  // Change the default widget for fields of type 'foo'.
+  if (isset($info['foo'])) {
+    $info['foo']['default widget'] = 'mymodule_widget';
+  }
+}
+
+/**
+ * Define the Field API schema for a field structure.
+ *
+ * This hook MUST be defined in .install for it to be detected during
+ * installation and upgrade.
+ *
+ * @param $field
+ *   A field structure.
+ *
+ * @return
+ *   An associative array with the following keys:
+ *   - columns: An array of Schema API column specifications, keyed by column
+ *     name. This specifies what comprises a value for a given field. For
+ *     example, a value for a number field is simply 'value', while a value for
+ *     a formatted text field is the combination of 'value' and 'format'. It is
+ *     recommended to avoid having the column definitions depend on field
+ *     settings when possible. No assumptions should be made on how storage
+ *     engines internally use the original column name to structure their
+ *     storage.
+ *   - indexes: (optional) An array of Schema API indexes definitions. Only
+ *     columns that appear in the 'columns' array are allowed. Those indexes
+ *     will be used as default indexes. Callers of field_create_field() can
+ *     specify additional indexes, or, at their own risk, modify the default
+ *     indexes specified by the field-type module. Some storage engines might
+ *     not support indexes.
+ *   - foreign keys: (optional) An array of Schema API foreign keys
+ *     definitions.
+ */
+function hook_field_schema($field) {
+  if ($field['type'] == 'text_long') {
+    $columns = array(
+      'value' => array(
+        'type' => 'text',
+        'size' => 'big',
+        'not null' => FALSE,
+      ),
+    );
+  }
+  else {
+    $columns = array(
+      'value' => array(
+        'type' => 'varchar',
+        'length' => $field['settings']['max_length'],
+        'not null' => FALSE,
+      ),
+    );
+  }
+  $columns += array(
+    'format' => array(
+      'type' => 'varchar',
+      'length' => 255,
+      'not null' => FALSE,
+    ),
+  );
+  return array(
+    'columns' => $columns,
+    'indexes' => array(
+      'format' => array('format'),
+    ),
+    'foreign keys' => array(
+      'format' => array(
+        'table' => 'filter_format',
+        'columns' => array('format' => 'format'),
+      ),
+    ),
+  );
+}
+
+/**
+ * Define custom load behavior for this module's field types.
+ *
+ * Unlike most other field hooks, this hook operates on multiple entities. The
+ * $entities, $instances and $items parameters are arrays keyed by entity ID.
+ * For performance reasons, information for all available entity should be
+ * loaded in a single query where possible.
+ *
+ * Note that the changes made to the field values get cached by the field cache
+ * for subsequent loads. You should never use this hook to load fieldable
+ * entities, since this is likely to cause infinite recursions when
+ * hook_field_load() is run on those as well. Use
+ * hook_field_formatter_prepare_view() instead.
+ *
+ * Make changes or additions to field values by altering the $items parameter by
+ * reference. There is no return value.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entities
+ *   Array of entities being loaded, keyed by entity ID.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instances
+ *   Array of instance structures for $field for each entity, keyed by entity
+ *   ID.
+ * @param $langcode
+ *   The language code associated with $items.
+ * @param $items
+ *   Array of field values already loaded for the entities, keyed by entity ID.
+ *   Store your changes in this parameter (passed by reference).
+ * @param $age
+ *   FIELD_LOAD_CURRENT to load the most recent revision for all fields, or
+ *   FIELD_LOAD_REVISION to load the version indicated by each entity.
+ */
+function hook_field_load($entity_type, $entities, $field, $instances, $langcode, &$items, $age) {
+  // Sample code from text.module: precompute sanitized strings so they are
+  // stored in the field cache.
+  foreach ($entities as $id => $entity) {
+    foreach ($items[$id] as $delta => $item) {
+      // Only process items with a cacheable format, the rest will be handled
+      // by formatters if needed.
+      if (empty($instances[$id]['settings']['text_processing']) || filter_format_allowcache($item['format'])) {
+        $items[$id][$delta]['safe_value'] = isset($item['value']) ? _text_sanitize($instances[$id], $langcode, $item, 'value') : '';
+        if ($field['type'] == 'text_with_summary') {
+          $items[$id][$delta]['safe_summary'] = isset($item['summary']) ? _text_sanitize($instances[$id], $langcode, $item, 'summary') : '';
+        }
+      }
+    }
+  }
+}
+
+/**
+ * Prepare field values prior to display.
+ *
+ * This hook is invoked before the field values are handed to formatters
+ * for display, and runs before the formatters' own
+ * hook_field_formatter_prepare_view().
+ *
+ * Unlike most other field hooks, this hook operates on multiple entities. The
+ * $entities, $instances and $items parameters are arrays keyed by entity ID.
+ * For performance reasons, information for all available entities should be
+ * loaded in a single query where possible.
+ *
+ * Make changes or additions to field values by altering the $items parameter by
+ * reference. There is no return value.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entities
+ *   Array of entities being displayed, keyed by entity ID.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instances
+ *   Array of instance structures for $field for each entity, keyed by entity
+ *   ID.
+ * @param $langcode
+ *   The language associated to $items.
+ * @param $items
+ *   $entity->{$field['field_name']}, or an empty array if unset.
+ */
+function hook_field_prepare_view($entity_type, $entities, $field, $instances, $langcode, &$items) {
+  // Sample code from image.module: if there are no images specified at all,
+  // use the default image.
+  foreach ($entities as $id => $entity) {
+    if (empty($items[$id]) && $field['settings']['default_image']) {
+      if ($file = file_load($field['settings']['default_image'])) {
+        $items[$id][0] = (array) $file + array(
+          'is_default' => TRUE,
+          'alt' => '',
+          'title' => '',
+        );
+      }
+    }
+  }
+}
+
+/**
+ * Validate this module's field data.
+ *
+ * If there are validation problems, add to the $errors array (passed by
+ * reference). There is no return value.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ * @param $errors
+ *   The array of errors (keyed by field name, language code, and delta) that
+ *   have already been reported for the entity. The function should add its
+ *   errors to this array. Each error is an associative array with the following
+ *   keys and values:
+ *   - error: An error code (should be a string prefixed with the module name).
+ *   - message: The human readable message to be displayed.
+ */
+function hook_field_validate($entity_type, $entity, $field, $instance, $langcode, $items, &$errors) {
+  foreach ($items as $delta => $item) {
+    if (!empty($item['value'])) {
+      if (!empty($field['settings']['max_length']) && drupal_strlen($item['value']) > $field['settings']['max_length']) {
+        $errors[$field['field_name']][$langcode][$delta][] = array(
+          'error' => 'text_max_length',
+          'message' => t('%name: the value may not be longer than %max characters.', array('%name' => $instance['label'], '%max' => $field['settings']['max_length'])),
+        );
+      }
+    }
+  }
+}
+
+/**
+ * Define custom presave behavior for this module's field types.
+ *
+ * Make changes or additions to field values by altering the $items parameter by
+ * reference. There is no return value.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ */
+function hook_field_presave($entity_type, $entity, $field, $instance, $langcode, &$items) {
+  if ($field['type'] == 'number_decimal') {
+    // Let PHP round the value to ensure consistent behavior across storage
+    // backends.
+    foreach ($items as $delta => $item) {
+      if (isset($item['value'])) {
+        $items[$delta]['value'] = round($item['value'], $field['settings']['scale']);
+      }
+    }
+  }
+}
+
+/**
+ * Define custom insert behavior for this module's field data.
+ *
+ * This hook is invoked from field_attach_insert() on the module that defines a
+ * field, during the process of inserting an entity object (node, taxonomy term,
+ * etc.). It is invoked just before the data for this field on the particular
+ * entity object is inserted into field storage. Only field modules that are
+ * storing or tracking information outside the standard field storage mechanism
+ * need to implement this hook.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ *
+ * @see hook_field_update()
+ * @see hook_field_delete()
+ */
+function hook_field_insert($entity_type, $entity, $field, $instance, $langcode, &$items) {
+  if (variable_get('taxonomy_maintain_index_table', TRUE) && $field['storage']['type'] == 'field_sql_storage' && $entity_type == 'node' && $entity->status) {
+    $query = db_insert('taxonomy_index')->fields(array('nid', 'tid', 'sticky', 'created', ));
+    foreach ($items as $item) {
+      $query->values(array(
+        'nid' => $entity->nid,
+        'tid' => $item['tid'],
+        'sticky' => $entity->sticky,
+        'created' => $entity->created,
+      ));
+    }
+    $query->execute();
+  }
+}
+
+/**
+ * Define custom update behavior for this module's field data.
+ *
+ * This hook is invoked from field_attach_update() on the module that defines a
+ * field, during the process of updating an entity object (node, taxonomy term,
+ * etc.). It is invoked just before the data for this field on the particular
+ * entity object is updated into field storage. Only field modules that are
+ * storing or tracking information outside the standard field storage mechanism
+ * need to implement this hook.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ *
+ * @see hook_field_insert()
+ * @see hook_field_delete()
+ */
+function hook_field_update($entity_type, $entity, $field, $instance, $langcode, &$items) {
+  if (variable_get('taxonomy_maintain_index_table', TRUE) && $field['storage']['type'] == 'field_sql_storage' && $entity_type == 'node') {
+    $first_call = &drupal_static(__FUNCTION__, array());
+
+    // We don't maintain data for old revisions, so clear all previous values
+    // from the table. Since this hook runs once per field, per object, make
+    // sure we only wipe values once.
+    if (!isset($first_call[$entity->nid])) {
+      $first_call[$entity->nid] = FALSE;
+      db_delete('taxonomy_index')->condition('nid', $entity->nid)->execute();
+    }
+    // Only save data to the table if the node is published.
+    if ($entity->status) {
+      $query = db_insert('taxonomy_index')->fields(array('nid', 'tid', 'sticky', 'created'));
+      foreach ($items as $item) {
+        $query->values(array(
+          'nid' => $entity->nid,
+          'tid' => $item['tid'],
+          'sticky' => $entity->sticky,
+          'created' => $entity->created,
+        ));
+      }
+      $query->execute();
+    }
+  }
+}
+
+/**
+ * Update the storage information for a field.
+ *
+ * This is invoked on the field's storage module from field_update_field(),
+ * before the new field information is saved to the database. The field storage
+ * module should update its storage tables to agree with the new field
+ * information. If there is a problem, the field storage module should throw an
+ * exception.
+ *
+ * @param $field
+ *   The updated field structure to be saved.
+ * @param $prior_field
+ *   The previously-saved field structure.
+ * @param $has_data
+ *   TRUE if the field has data in storage currently.
+ */
+function hook_field_storage_update_field($field, $prior_field, $has_data) {
+  if (!$has_data) {
+    // There is no data. Re-create the tables completely.
+    $prior_schema = _field_sql_storage_schema($prior_field);
+    foreach ($prior_schema as $name => $table) {
+      db_drop_table($name, $table);
+    }
+    $schema = _field_sql_storage_schema($field);
+    foreach ($schema as $name => $table) {
+      db_create_table($name, $table);
+    }
+  }
+  else {
+    // There is data. See field_sql_storage_field_storage_update_field() for
+    // an example of what to do to modify the schema in place, preserving the
+    // old data as much as possible.
+  }
+  drupal_get_schema(NULL, TRUE);
+}
+
+/**
+ * Define custom delete behavior for this module's field data.
+ *
+ * This hook is invoked from field_attach_delete() on the module that defines a
+ * field, during the process of deleting an entity object (node, taxonomy term,
+ * etc.). It is invoked just before the data for this field on the particular
+ * entity object is deleted from field storage. Only field modules that are
+ * storing or tracking information outside the standard field storage mechanism
+ * need to implement this hook.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ *
+ * @see hook_field_insert()
+ * @see hook_field_update()
+ */
+function hook_field_delete($entity_type, $entity, $field, $instance, $langcode, &$items) {
+  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
+  foreach ($items as $delta => $item) {
+    // For hook_file_references(), remember that this is being deleted.
+    $item['file_field_name'] = $field['field_name'];
+    // Pass in the ID of the object that is being removed so all references can
+    // be counted in hook_file_references().
+    $item['file_field_type'] = $entity_type;
+    $item['file_field_id'] = $id;
+    file_field_delete_file($item, $field, $entity_type, $id);
+  }
+}
+
+/**
+ * Define custom revision delete behavior for this module's field types.
+ *
+ * This hook is invoked just before the data is deleted from field storage
+ * in field_attach_delete_revision(), and will only be called for fieldable
+ * types that are versioned.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ */
+function hook_field_delete_revision($entity_type, $entity, $field, $instance, $langcode, &$items) {
+  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
+  foreach ($items as $delta => $item) {
+    // For hook_file_references, remember that this file is being deleted.
+    $item['file_field_name'] = $field['field_name'];
+    if (file_field_delete_file($item, $field, $entity_type, $id)) {
+      $items[$delta] = NULL;
+    }
+  }
+}
+
+/**
+ * Define custom prepare_translation behavior for this module's field types.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity for the operation.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instance
+ *   The instance structure for $field on $entity's bundle.
+ * @param $langcode
+ *   The language associated to $items.
+ * @param $items
+ *   $entity->{$field['field_name']}[$langcode], or an empty array if unset.
+ * @param $source_entity
+ *   The source entity from which field values are being copied.
+ * @param $source_langcode
+ *   The source language from which field values are being copied.
+ */
+function hook_field_prepare_translation($entity_type, $entity, $field, $instance, $langcode, &$items, $source_entity, $source_langcode) {
+  // If the translating user is not permitted to use the assigned text format,
+  // we must not expose the source values.
+  $field_name = $field['field_name'];
+  $formats = filter_formats();
+  $format_id = $source_entity->{$field_name}[$source_langcode][0]['format'];
+  if (!filter_access($formats[$format_id])) {
+    $items = array();
+  }
+}
+
+/**
+ * Define what constitutes an empty item for a field type.
+ *
+ * @param $item
+ *   An item that may or may not be empty.
+ * @param $field
+ *   The field to which $item belongs.
+ *
+ * @return
+ *   TRUE if $field's type considers $item not to contain any data;
+ *   FALSE otherwise.
+ */
+function hook_field_is_empty($item, $field) {
+  if (empty($item['value']) && (string) $item['value'] !== '0') {
+    return TRUE;
+  }
+  return FALSE;
+}
+
+/**
+ * @} End of "defgroup field_types".
+ */
+
+/**
+ * @defgroup field_widget Field Widget API
+ * @{
+ * Define Field API widget types.
+ *
+ * Field API widgets specify how fields are displayed in edit forms. Fields of a
+ * given @link field_types field type @endlink may be edited using more than one
+ * widget. In this case, the Field UI module allows the site builder to choose
+ * which widget to use. Widget types are defined by implementing
+ * hook_field_widget_info().
+ *
+ * Widgets are @link forms_api_reference.html Form API @endlink elements with
+ * additional processing capabilities. Widget hooks are typically called by the
+ * Field Attach API during the creation of the field form structure with
+ * field_attach_form().
+ *
+ * @see field
+ * @see field_types
+ * @see field_formatter
+ */
+
+/**
+ * Expose Field API widget types.
+ *
+ * @return
+ *   An array describing the widget types implemented by the module.
+ *   The keys are widget type names. To avoid name clashes, widget type
+ *   names should be prefixed with the name of the module that exposes them.
+ *   The values are arrays describing the widget type, with the following
+ *   key/value pairs:
+ *   - label: The human-readable name of the widget type.
+ *   - description: A short description for the widget type.
+ *   - field types: An array of field types the widget supports.
+ *   - settings: An array whose keys are the names of the settings available
+ *     for the widget type, and whose values are the default values for those
+ *     settings.
+ *   - behaviors: (optional) An array describing behaviors of the widget, with
+ *     the following elements:
+ *     - multiple values: One of the following constants:
+ *       - FIELD_BEHAVIOR_DEFAULT: (default) If the widget allows the input of
+ *         one single field value (most common case). The widget will be
+ *         repeated for each value input.
+ *       - FIELD_BEHAVIOR_CUSTOM: If one single copy of the widget can receive
+ *         several field values. Examples: checkboxes, multiple select,
+ *         comma-separated textfield.
+ *     - default value: One of the following constants:
+ *       - FIELD_BEHAVIOR_DEFAULT: (default) If the widget accepts default
+ *         values.
+ *       - FIELD_BEHAVIOR_NONE: if the widget does not support default values.
+ *   - weight: (optional) An integer to determine the weight of this widget
+ *     relative to other widgets in the Field UI when selecting a widget for a
+ *     given field instance.
+ *
+ * @see hook_field_widget_info_alter()
+ * @see hook_field_widget_form()
+ * @see hook_field_widget_form_alter()
+ * @see hook_field_widget_WIDGET_TYPE_form_alter()
+ * @see hook_field_widget_error()
+ * @see hook_field_widget_settings_form()
+ */
+function hook_field_widget_info() {
+  return array(
+    'text_textfield' => array(
+      'label' => t('Text field'),
+      'field types' => array('text'),
+      'settings' => array('size' => 60),
+      'behaviors' => array(
+        'multiple values' => FIELD_BEHAVIOR_DEFAULT,
+        'default value' => FIELD_BEHAVIOR_DEFAULT,
+      ),
+    ),
+    'text_textarea' => array(
+      'label' => t('Text area (multiple rows)'),
+      'field types' => array('text_long'),
+      'settings' => array('rows' => 5),
+      'behaviors' => array(
+        'multiple values' => FIELD_BEHAVIOR_DEFAULT,
+        'default value' => FIELD_BEHAVIOR_DEFAULT,
+      ),
+    ),
+    'text_textarea_with_summary' => array(
+      'label' => t('Text area with a summary'),
+      'field types' => array('text_with_summary'),
+      'settings' => array('rows' => 20, 'summary_rows' => 5),
+      'behaviors' => array(
+        'multiple values' => FIELD_BEHAVIOR_DEFAULT,
+        'default value' => FIELD_BEHAVIOR_DEFAULT,
+      ),
+      // As an advanced widget, force it to sink to the bottom of the choices.
+      'weight' => 2,
+    ),
+  );
+}
+
+/**
+ * Perform alterations on Field API widget types.
+ *
+ * @param $info
+ *   Array of informations on widget types exposed by hook_field_widget_info()
+ *   implementations.
+ */
+function hook_field_widget_info_alter(&$info) {
+  // Add a setting to a widget type.
+  $info['text_textfield']['settings'] += array(
+    'mymodule_additional_setting' => 'default value',
+  );
+
+  // Let a new field type re-use an existing widget.
+  $info['options_select']['field types'][] = 'my_field_type';
+}
+
+/**
+ * Return the form for a single field widget.
+ *
+ * Field widget form elements should be based on the passed-in $element, which
+ * contains the base form element properties derived from the field
+ * configuration.
+ *
+ * Field API will set the weight, field name and delta values for each form
+ * element. If there are multiple values for this field, the Field API will
+ * invoke this hook as many times as needed.
+ *
+ * Note that, depending on the context in which the widget is being included
+ * (regular entity form, field configuration form, advanced search form...),
+ * the values for $field and $instance might be different from the "official"
+ * definitions returned by field_info_field() and field_info_instance().
+ * Examples: mono-value widget even if the field is multi-valued, non-required
+ * widget even if the field is 'required'...
+ *
+ * Therefore, the FAPI element callbacks (such as #process, #element_validate,
+ * #value_callback...) used by the widget cannot use the field_info_field()
+ * or field_info_instance() functions to retrieve the $field or $instance
+ * definitions they should operate on. The field_widget_field() and
+ * field_widget_instance() functions should be used instead to fetch the
+ * current working definitions from $form_state, where Field API stores them.
+ *
+ * Alternatively, hook_field_widget_form() can extract the needed specific
+ * properties from $field and $instance and set them as ad-hoc
+ * $element['#custom'] properties, for later use by its element callbacks.
+ *
+ * Other modules may alter the form element provided by this function using
+ * hook_field_widget_form_alter().
+ *
+ * @param $form
+ *   The form structure where widgets are being attached to. This might be a
+ *   full form structure, or a sub-element of a larger form.
+ * @param $form_state
+ *   An associative array containing the current state of the form.
+ * @param $field
+ *   The field structure.
+ * @param $instance
+ *   The field instance.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   Array of default values for this field.
+ * @param $delta
+ *   The order of this item in the array of subelements (0, 1, 2, etc).
+ * @param $element
+ *   A form element array containing basic properties for the widget:
+ *   - #entity_type: The name of the entity the field is attached to.
+ *   - #bundle: The name of the field bundle the field is contained in.
+ *   - #field_name: The name of the field.
+ *   - #language: The language the field is being edited in.
+ *   - #field_parents: The 'parents' space for the field in the form. Most
+ *       widgets can simply overlook this property. This identifies the
+ *       location where the field values are placed within
+ *       $form_state['values'], and is used to access processing information
+ *       for the field through the field_form_get_state() and
+ *       field_form_set_state() functions.
+ *   - #columns: A list of field storage columns of the field.
+ *   - #title: The sanitized element label for the field instance, ready for
+ *     output.
+ *   - #description: The sanitized element description for the field instance,
+ *     ready for output.
+ *   - #required: A Boolean indicating whether the element value is required;
+ *     for required multiple value fields, only the first widget's values are
+ *     required.
+ *   - #delta: The order of this item in the array of subelements; see $delta
+ *     above.
+ *
+ * @return
+ *   The form elements for a single widget for this field.
+ *
+ * @see field_widget_field()
+ * @see field_widget_instance()
+ * @see hook_field_widget_form_alter()
+ * @see hook_field_widget_WIDGET_TYPE_form_alter()
+ */
+function hook_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
+  $element += array(
+    '#type' => $instance['widget']['type'],
+    '#default_value' => isset($items[$delta]) ? $items[$delta] : '',
+  );
+  return array('value' => $element);
+}
+
+/**
+ * Alter forms for field widgets provided by other modules.
+ *
+ * @param $element
+ *   The field widget form element as constructed by hook_field_widget_form().
+ * @param $form_state
+ *   An associative array containing the current state of the form.
+ * @param $context
+ *   An associative array containing the following key-value pairs, matching the
+ *   arguments received by hook_field_widget_form():
+ *   - form: The form structure to which widgets are being attached. This may be
+ *     a full form structure, or a sub-element of a larger form.
+ *   - field: The field structure.
+ *   - instance: The field instance structure.
+ *   - langcode: The language associated with $items.
+ *   - items: Array of default values for this field.
+ *   - delta: The order of this item in the array of subelements (0, 1, 2, etc).
+ *
+ * @see hook_field_widget_form()
+ * @see hook_field_widget_WIDGET_TYPE_form_alter()
+ */
+function hook_field_widget_form_alter(&$element, &$form_state, $context) {
+  // Add a css class to widget form elements for all fields of type mytype.
+  if ($context['field']['type'] == 'mytype') {
+    // Be sure not to overwrite existing attributes.
+    $element['#attributes']['class'][] = 'myclass';
+  }
+}
+
+/**
+ * Alter widget forms for a specific widget provided by another module.
+ *
+ * Modules can implement hook_field_widget_WIDGET_TYPE_form_alter() to modify a
+ * specific widget form, rather than using hook_field_widget_form_alter() and
+ * checking the widget type.
+ *
+ * @param $element
+ *   The field widget form element as constructed by hook_field_widget_form().
+ * @param $form_state
+ *   An associative array containing the current state of the form.
+ * @param $context
+ *   An associative array containing the following key-value pairs, matching the
+ *   arguments received by hook_field_widget_form():
+ *   - "form": The form structure where widgets are being attached to. This
+ *     might be a full form structure, or a sub-element of a larger form.
+ *   - "field": The field structure.
+ *   - "instance": The field instance structure.
+ *   - "langcode": The language associated with $items.
+ *   - "items": Array of default values for this field.
+ *   - "delta": The order of this item in the array of subelements (0, 1, 2,
+ *     etc).
+ *
+ * @see hook_field_widget_form()
+ * @see hook_field_widget_form_alter()
+ */
+function hook_field_widget_WIDGET_TYPE_form_alter(&$element, &$form_state, $context) {
+  // Code here will only act on widgets of type WIDGET_TYPE.  For example,
+  // hook_field_widget_mymodule_autocomplete_form_alter() will only act on
+  // widgets of type 'mymodule_autocomplete'.
+  $element['#autocomplete_path'] = 'mymodule/autocomplete_path';
+}
+
+/**
+ * Alters the widget properties of a field instance before it gets displayed.
+ *
+ * Note that instead of hook_field_widget_properties_alter(), which is called
+ * for all fields on all entity types,
+ * hook_field_widget_properties_ENTITY_TYPE_alter() may be used to alter widget
+ * properties for fields on a specific entity type only.
+ *
+ * This hook is called once per field per added or edit entity. If the result
+ * of the hook involves reading from the database, it is highly recommended to
+ * statically cache the information.
+ *
+ * @param $widget
+ *   The instance's widget properties.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g., 'node' or 'user'.
+ *   - entity: The entity object.
+ *   - field: The field that the widget belongs to.
+ *   - instance: The instance of the field.
+ *
+ * @see hook_field_widget_properties_ENTITY_TYPE_alter()
+ */
+function hook_field_widget_properties_alter(&$widget, $context) {
+  // Change a widget's type according to the time of day.
+  $field = $context['field'];
+  if ($context['entity_type'] == 'node' && $field['field_name'] == 'field_foo') {
+    $time = date('H');
+    $widget['type'] = $time < 12 ? 'widget_am' : 'widget_pm';
+  }
+}
+
+/**
+ * Flag a field-level validation error.
+ *
+ * @param $element
+ *   An array containing the form element for the widget. The error needs to be
+ *   flagged on the right sub-element, according to the widget's internal
+ *   structure.
+ * @param $error
+ *   An associative array with the following key-value pairs, as returned by
+ *   hook_field_validate():
+ *   - error: the error code. Complex widgets might need to report different
+ *     errors to different form elements inside the widget.
+ *   - message: the human readable message to be displayed.
+ * @param $form
+ *   The form structure where field elements are attached to. This might be a
+ *   full form structure, or a sub-element of a larger form.
+ * @param $form_state
+ *   An associative array containing the current state of the form.
+ */
+function hook_field_widget_error($element, $error, $form, &$form_state) {
+  form_error($element, $error['message']);
+}
+
+
+/**
+ * @} End of "defgroup field_widget".
+ */
+
+
+/**
+ * @defgroup field_formatter Field Formatter API
+ * @{
+ * Define Field API formatter types.
+ *
+ * Field API formatters specify how fields are displayed when the entity to
+ * which the field is attached is displayed. Fields of a given
+ * @link field_types field type @endlink may be displayed using more than one
+ * formatter. In this case, the Field UI module allows the site builder to
+ * choose which formatter to use. Field formatters are defined by implementing
+ * hook_field_formatter_info().
+ *
+ * @see field
+ * @see field_types
+ * @see field_widget
+ */
+
+/**
+ * Expose Field API formatter types.
+ *
+ * Formatters handle the display of field values. Formatter hooks are typically
+ * called by the Field Attach API field_attach_prepare_view() and
+ * field_attach_view() functions.
+ *
+ * @return
+ *   An array describing the formatter types implemented by the module.
+ *   The keys are formatter type names. To avoid name clashes, formatter type
+ *   names should be prefixed with the name of the module that exposes them.
+ *   The values are arrays describing the formatter type, with the following
+ *   key/value pairs:
+ *   - label: The human-readable name of the formatter type.
+ *   - description: A short description for the formatter type.
+ *   - field types: An array of field types the formatter supports.
+ *   - settings: An array whose keys are the names of the settings available
+ *     for the formatter type, and whose values are the default values for
+ *     those settings.
+ *
+ * @see hook_field_formatter_info_alter()
+ * @see hook_field_formatter_view()
+ * @see hook_field_formatter_prepare_view()
+ */
+function hook_field_formatter_info() {
+  return array(
+    'text_default' => array(
+      'label' => t('Default'),
+      'field types' => array('text', 'text_long', 'text_with_summary'),
+    ),
+    'text_plain' => array(
+      'label' => t('Plain text'),
+      'field types' => array('text', 'text_long', 'text_with_summary'),
+    ),
+
+    // The text_trimmed formatter displays the trimmed version of the
+    // full element of the field. It is intended to be used with text
+    // and text_long fields. It also works with text_with_summary
+    // fields though the text_summary_or_trimmed formatter makes more
+    // sense for that field type.
+    'text_trimmed' => array(
+      'label' => t('Trimmed'),
+      'field types' => array('text', 'text_long', 'text_with_summary'),
+    ),
+
+    // The 'summary or trimmed' field formatter for text_with_summary
+    // fields displays returns the summary element of the field or, if
+    // the summary is empty, the trimmed version of the full element
+    // of the field.
+    'text_summary_or_trimmed' => array(
+      'label' => t('Summary or trimmed'),
+      'field types' => array('text_with_summary'),
+    ),
+  );
+}
+
+/**
+ * Perform alterations on Field API formatter types.
+ *
+ * @param $info
+ *   An array of information on formatter types exposed by
+ *   hook_field_formatter_info() implementations.
+ */
+function hook_field_formatter_info_alter(&$info) {
+  // Add a setting to a formatter type.
+  $info['text_default']['settings'] += array(
+    'mymodule_additional_setting' => 'default value',
+  );
+
+  // Let a new field type re-use an existing formatter.
+  $info['text_default']['field types'][] = 'my_field_type';
+}
+
+/**
+ * Allow formatters to load information for field values being displayed.
+ *
+ * This should be used when a formatter needs to load additional information
+ * from the database in order to render a field, for example a reference field
+ * which displays properties of the referenced entities such as name or type.
+ *
+ * This hook is called after the field type's own hook_field_prepare_view().
+ *
+ * Unlike most other field hooks, this hook operates on multiple entities. The
+ * $entities, $instances and $items parameters are arrays keyed by entity ID.
+ * For performance reasons, information for all available entities should be
+ * loaded in a single query where possible.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entities
+ *   Array of entities being displayed, keyed by entity ID.
+ * @param $field
+ *   The field structure for the operation.
+ * @param $instances
+ *   Array of instance structures for $field for each entity, keyed by entity
+ *   ID.
+ * @param $langcode
+ *   The language the field values are to be shown in. If no language is
+ *   provided the current language is used.
+ * @param $items
+ *   Array of field values for the entities, keyed by entity ID.
+ * @param $displays
+ *   Array of display settings to use for each entity, keyed by entity ID.
+ *
+ * @return
+ *   Changes or additions to field values are done by altering the $items
+ *   parameter by reference.
+ */
+function hook_field_formatter_prepare_view($entity_type, $entities, $field, $instances, $langcode, &$items, $displays) {
+  $tids = array();
+
+  // Collect every possible term attached to any of the fieldable entities.
+  foreach ($entities as $id => $entity) {
+    foreach ($items[$id] as $delta => $item) {
+      // Force the array key to prevent duplicates.
+      $tids[$item['tid']] = $item['tid'];
+    }
+  }
+
+  if ($tids) {
+    $terms = taxonomy_term_load_multiple($tids);
+
+    // Iterate through the fieldable entities again to attach the loaded term
+    // data.
+    foreach ($entities as $id => $entity) {
+      $rekey = FALSE;
+
+      foreach ($items[$id] as $delta => $item) {
+        // Check whether the taxonomy term field instance value could be loaded.
+        if (isset($terms[$item['tid']])) {
+          // Replace the instance value with the term data.
+          $items[$id][$delta]['taxonomy_term'] = $terms[$item['tid']];
+        }
+        // Otherwise, unset the instance value, since the term does not exist.
+        else {
+          unset($items[$id][$delta]);
+          $rekey = TRUE;
+        }
+      }
+
+      if ($rekey) {
+        // Rekey the items array.
+        $items[$id] = array_values($items[$id]);
+      }
+    }
+  }
+}
+
+/**
+ * Build a renderable array for a field value.
+ *
+ * @param $entity_type
+ *   The type of $entity.
+ * @param $entity
+ *   The entity being displayed.
+ * @param $field
+ *   The field structure.
+ * @param $instance
+ *   The field instance.
+ * @param $langcode
+ *   The language associated with $items.
+ * @param $items
+ *   Array of values for this field.
+ * @param $display
+ *   The display settings to use, as found in the 'display' entry of instance
+ *   definitions. The array notably contains the following keys and values;
+ *   - type: The name of the formatter to use.
+ *   - settings: The array of formatter settings.
+ *
+ * @return
+ *   A renderable array for the $items, as an array of child elements keyed
+ *   by numeric indexes starting from 0.
+ */
+function hook_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display) {
+  $element = array();
+  $settings = $display['settings'];
+
+  switch ($display['type']) {
+    case 'sample_field_formatter_simple':
+      // Common case: each value is displayed individually in a sub-element
+      // keyed by delta. The field.tpl.php template specifies the markup
+      // wrapping each value.
+      foreach ($items as $delta => $item) {
+        $element[$delta] = array('#markup' => $settings['some_setting'] . $item['value']);
+      }
+      break;
+
+    case 'sample_field_formatter_themeable':
+      // More elaborate formatters can defer to a theme function for easier
+      // customization.
+      foreach ($items as $delta => $item) {
+        $element[$delta] = array(
+          '#theme' => 'mymodule_theme_sample_field_formatter_themeable',
+          '#data' => $item['value'],
+          '#some_setting' => $settings['some_setting'],
+        );
+      }
+      break;
+
+    case 'sample_field_formatter_combined':
+      // Some formatters might need to display all values within a single piece
+      // of markup.
+      $rows = array();
+      foreach ($items as $delta => $item) {
+        $rows[] = array($delta, $item['value']);
+      }
+      $element[0] = array(
+        '#theme' => 'table',
+        '#header' => array(t('Delta'), t('Value')),
+        '#rows' => $rows,
+      );
+      break;
+  }
+
+  return $element;
+}
+
+/**
+ * @} End of "defgroup field_formatter".
+ */
+
+/**
+ * @ingroup field_attach
+ * @{
+ */
+
+/**
+ * Act on field_attach_form().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ * Implementing modules should alter the $form or $form_state parameters.
+ *
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   The entity for which an edit form is being built.
+ * @param $form
+ *   The form structure where field elements are attached to. This might be a
+ *   full form structure, or a sub-element of a larger form. The
+ *   $form['#parents'] property can be used to identify the corresponding part
+ *   of $form_state['values']. Hook implementations that need to act on the
+ *   top-level properties of the global form (like #submit, #validate...) can
+ *   add a #process callback to the array received in the $form parameter, and
+ *   act on the $complete_form parameter in the process callback.
+ * @param $form_state
+ *   An associative array containing the current state of the form.
+ * @param $langcode
+ *   The language the field values are going to be entered in. If no language
+ *   is provided the default site language will be used.
+ */
+function hook_field_attach_form($entity_type, $entity, &$form, &$form_state, $langcode) {
+  // Add a checkbox allowing a given field to be emptied.
+  // See hook_field_attach_submit() for the corresponding processing code.
+  $form['empty_field_foo'] = array(
+    '#type' => 'checkbox',
+    '#title' => t("Empty the 'field_foo' field"),
+  );
+}
+
+/**
+ * Act on field_attach_load().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * Unlike other field_attach hooks, this hook accounts for 'multiple loads'.
+ * Instead of the usual $entity parameter, it accepts an array of entities,
+ * indexed by entity ID. For performance reasons, information for all available
+ * entities should be loaded in a single query where possible.
+ *
+ * The changes made to the entities' field values get cached by the field cache
+ * for subsequent loads.
+ *
+ * See field_attach_load() for details and arguments.
+ */
+function hook_field_attach_load($entity_type, $entities, $age, $options) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_attach_validate().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_validate() for details and arguments.
+ */
+function hook_field_attach_validate($entity_type, $entity, &$errors) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_attach_submit().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   The entity for which an edit form is being submitted. The incoming form
+ *   values have been extracted as field values of the $entity object.
+ * @param $form
+ *   The form structure where field elements are attached to. This might be a
+ *   full form structure, or a sub-part of a larger form. The $form['#parents']
+ *   property can be used to identify the corresponding part of
+ *   $form_state['values'].
+ * @param $form_state
+ *   An associative array containing the current state of the form.
+ */
+function hook_field_attach_submit($entity_type, $entity, $form, &$form_state) {
+  // Sample case of an 'Empty the field' checkbox added on the form, allowing
+  // a given field to be emptied.
+  $values = drupal_array_get_nested_value($form_state['values'], $form['#parents']);
+  if (!empty($values['empty_field_foo'])) {
+    unset($entity->field_foo);
+  }
+}
+
+/**
+ * Act on field_attach_presave().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_presave() for details and arguments.
+ */
+function hook_field_attach_presave($entity_type, $entity) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_attach_insert().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_insert() for details and arguments.
+ */
+function hook_field_attach_insert($entity_type, $entity) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_attach_update().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_update() for details and arguments.
+ */
+function hook_field_attach_update($entity_type, $entity) {
+  // @todo Needs function body.
+}
+
+/**
+ * Alter field_attach_preprocess() variables.
+ *
+ * This hook is invoked while preprocessing the field.tpl.php template file
+ * in field_attach_preprocess().
+ *
+ * @param $variables
+ *   The variables array is passed by reference and will be populated with field
+ *   values.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The type of $entity; for example, 'node' or 'user'.
+ *   - entity: The entity with fields to render.
+ *   - element: The structured array containing the values ready for rendering.
+ */
+function hook_field_attach_preprocess_alter(&$variables, $context) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_attach_delete().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_delete() for details and arguments.
+ */
+function hook_field_attach_delete($entity_type, $entity) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_attach_delete_revision().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_delete_revision() for details and arguments.
+ */
+function hook_field_attach_delete_revision($entity_type, $entity) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field_purge_data().
+ *
+ * This hook is invoked in field_purge_data() and allows modules to act on
+ * purging data from a single field pseudo-entity. For example, if a module
+ * relates data in the field with its own data, it may purge its own data
+ * during this process as well.
+ *
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   The pseudo-entity whose field data is being purged.
+ * @param $field
+ *   The (possibly deleted) field whose data is being purged.
+ * @param $instance
+ *   The deleted field instance whose data is being purged.
+ *
+ * @see @link field_purge Field API bulk data deletion @endlink
+ * @see field_purge_data()
+ */
+function hook_field_attach_purge($entity_type, $entity, $field, $instance) {
+  // find the corresponding data in mymodule and purge it
+  if ($entity_type == 'node' && $field->field_name == 'my_field_name') {
+    mymodule_remove_mydata($entity->nid);
+  }
+}
+
+/**
+ * Perform alterations on field_attach_view() or field_view_field().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * @param $output
+ *   The structured content array tree for all of the entity's fields.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The type of $entity; for example, 'node' or 'user'.
+ *   - entity: The entity with fields to render.
+ *   - view_mode: View mode; for example, 'full' or 'teaser'.
+ *   - display: Either a view mode string or an array of display settings. If
+ *     this hook is being invoked from field_attach_view(), the 'display'
+ *     element is set to the view mode string. If this hook is being invoked
+ *     from field_view_field(), this element is set to the $display argument
+ *     and the view_mode element is set to '_custom'. See field_view_field()
+ *     for more information on what its $display argument contains.
+ *   - language: The language code used for rendering.
+ */
+function hook_field_attach_view_alter(&$output, $context) {
+  // Append RDF term mappings on displayed taxonomy links.
+  foreach (element_children($output) as $field_name) {
+    $element = &$output[$field_name];
+    if ($element['#field_type'] == 'taxonomy_term_reference' && $element['#formatter'] == 'taxonomy_term_reference_link') {
+      foreach ($element['#items'] as $delta => $item) {
+        $term = $item['taxonomy_term'];
+        if (!empty($term->rdf_mapping['rdftype'])) {
+          $element[$delta]['#options']['attributes']['typeof'] = $term->rdf_mapping['rdftype'];
+        }
+        if (!empty($term->rdf_mapping['name']['predicates'])) {
+          $element[$delta]['#options']['attributes']['property'] = $term->rdf_mapping['name']['predicates'];
+        }
+      }
+    }
+  }
+}
+
+/**
+ * Perform alterations on field_attach_prepare_translation().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * @param $entity
+ *   The entity being prepared for translation.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The type of $entity; e.g. 'node' or 'user'.
+ *   - langcode: The language the entity has to be translated in.
+ *   - source_entity: The entity holding the field values to be translated.
+ *   - source_langcode: The source language from which translate.
+ */
+function hook_field_attach_prepare_translation_alter(&$entity, $context) {
+  if ($context['entity_type'] == 'custom_entity_type') {
+    $entity->custom_field = $context['source_entity']->custom_field;
+  }
+}
+
+/**
+ * Perform alterations on field_language() values.
+ *
+ * This hook is invoked to alter the array of display languages for the given
+ * entity.
+ *
+ * @param $display_language
+ *   A reference to an array of language codes keyed by field name.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The type of the entity to be displayed.
+ *   - entity: The entity with fields to render.
+ *   - langcode: The language code $entity has to be displayed in.
+ */
+function hook_field_language_alter(&$display_language, $context) {
+  // Do not apply core language fallback rules if they are disabled or if Locale
+  // is not registered as a translation handler.
+  if (variable_get('locale_field_language_fallback', TRUE) && field_has_translation_handler($context['entity_type'], 'locale')) {
+    locale_field_language_fallback($display_language, $context['entity'], $context['language']);
+  }
+}
+
+/**
+ * Alter field_available_languages() values.
+ *
+ * This hook is invoked from field_available_languages() to allow modules to
+ * alter the array of available languages for the given field.
+ *
+ * @param $languages
+ *   A reference to an array of language codes to be made available.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The type of the entity the field is attached to.
+ *   - field: A field data structure.
+ */
+function hook_field_available_languages_alter(&$languages, $context) {
+  // Add an unavailable language.
+  $languages[] = 'xx';
+
+  // Remove an available language.
+  $index = array_search('yy', $languages);
+  unset($languages[$index]);
+}
+
+/**
+ * Act on field_attach_create_bundle().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_create_bundle() for details and arguments.
+ */
+function hook_field_attach_create_bundle($entity_type, $bundle) {
+  // When a new bundle is created, the menu needs to be rebuilt to add the
+  // Field UI menu item tabs.
+  variable_set('menu_rebuild_needed', TRUE);
+}
+
+/**
+ * Act on field_attach_rename_bundle().
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * See field_attach_rename_bundle() for details and arguments.
+ */
+function hook_field_attach_rename_bundle($entity_type, $bundle_old, $bundle_new) {
+  // Update the extra weights variable with new information.
+  if ($bundle_old !== $bundle_new) {
+    $extra_weights = variable_get('field_extra_weights', array());
+    if (isset($info[$entity_type][$bundle_old])) {
+      $extra_weights[$entity_type][$bundle_new] = $extra_weights[$entity_type][$bundle_old];
+      unset($extra_weights[$entity_type][$bundle_old]);
+      variable_set('field_extra_weights', $extra_weights);
+    }
+  }
+}
+
+/**
+ * Act on field_attach_delete_bundle.
+ *
+ * This hook is invoked after the field module has performed the operation.
+ *
+ * @param $entity_type
+ *   The type of entity; for example, 'node' or 'user'.
+ * @param $bundle
+ *   The bundle that was just deleted.
+ * @param $instances
+ *   An array of all instances that existed for the bundle before it was
+ *   deleted.
+ */
+function hook_field_attach_delete_bundle($entity_type, $bundle, $instances) {
+  // Remove the extra weights variable information for this bundle.
+  $extra_weights = variable_get('field_extra_weights', array());
+  if (isset($extra_weights[$entity_type][$bundle])) {
+    unset($extra_weights[$entity_type][$bundle]);
+    variable_set('field_extra_weights', $extra_weights);
+  }
+}
+
+/**
+ * @} End of "defgroup field_attach".
+ */
+
+/**
+ * @addtogroup field_storage
+ * @{
+ */
+
+/**
+ * Expose Field API storage backends.
+ *
+ * @return
+ *   An array describing the storage backends implemented by the module.
+ *   The keys are storage backend names. To avoid name clashes, storage backend
+ *   names should be prefixed with the name of the module that exposes them.
+ *   The values are arrays describing the storage backend, with the following
+ *   key/value pairs:
+ *   - label: The human-readable name of the storage backend.
+ *   - description: A short description for the storage backend.
+ *   - settings: An array whose keys are the names of the settings available
+ *     for the storage backend, and whose values are the default values for
+ *     those settings.
+ */
+function hook_field_storage_info() {
+  return array(
+    'field_sql_storage' => array(
+      'label' => t('Default SQL storage'),
+      'description' => t('Stores fields in the local SQL database, using per-field tables.'),
+      'settings' => array(),
+    ),
+  );
+}
+
+/**
+ * Perform alterations on Field API storage types.
+ *
+ * @param $info
+ *   Array of informations on storage types exposed by
+ *   hook_field_field_storage_info() implementations.
+ */
+function hook_field_storage_info_alter(&$info) {
+  // Add a setting to a storage type.
+  $info['field_sql_storage']['settings'] += array(
+    'mymodule_additional_setting' => 'default value',
+  );
+}
+
+/**
+ * Reveal the internal details about the storage for a field.
+ *
+ * For example, an SQL storage module might return the Schema API structure for
+ * the table. A key/value storage module might return the server name,
+ * authentication credentials, and bin name.
+ *
+ * Field storage modules are not obligated to implement this hook. Modules
+ * that rely on these details must only use them for read operations.
+ *
+ * @param $field
+ *   A field structure.
+ *
+ * @return
+ *   An array of details.
+ *    - The first dimension is a store type (sql, solr, etc).
+ *    - The second dimension indicates the age of the values in the store
+ *      FIELD_LOAD_CURRENT or FIELD_LOAD_REVISION.
+ *    - Other dimensions are specific to the field storage module.
+ *
+ * @see hook_field_storage_details_alter()
+ */
+function hook_field_storage_details($field) {
+  $details = array();
+
+  // Add field columns.
+  foreach ((array) $field['columns'] as $column_name => $attributes) {
+    $real_name = _field_sql_storage_columnname($field['field_name'], $column_name);
+    $columns[$column_name] = $real_name;
+  }
+  return array(
+    'sql' => array(
+      FIELD_LOAD_CURRENT => array(
+        _field_sql_storage_tablename($field) => $columns,
+      ),
+      FIELD_LOAD_REVISION => array(
+        _field_sql_storage_revision_tablename($field) => $columns,
+      ),
+    ),
+  );
+}
+
+/**
+ * Perform alterations on Field API storage details.
+ *
+ * @param $details
+ *   An array of storage details for fields as exposed by
+ *   hook_field_storage_details() implementations.
+ * @param $field
+ *   A field structure.
+ *
+ * @see hook_field_storage_details()
+ */
+function hook_field_storage_details_alter(&$details, $field) {
+  if ($field['field_name'] == 'field_of_interest') {
+    $columns = array();
+    foreach ((array) $field['columns'] as $column_name => $attributes) {
+      $columns[$column_name] = $column_name;
+    }
+    $details['drupal_variables'] = array(
+      FIELD_LOAD_CURRENT => array(
+        'moon' => $columns,
+      ),
+      FIELD_LOAD_REVISION => array(
+        'mars' => $columns,
+      ),
+    );
+  }
+}
+
+/**
+ * Load field data for a set of entities.
+ *
+ * This hook is invoked from field_attach_load() to ask the field storage
+ * module to load field data.
+ *
+ * Modules implementing this hook should load field values and add them to
+ * objects in $entities. Fields with no values should be added as empty
+ * arrays.
+ *
+ * @param $entity_type
+ *   The type of entity, such as 'node' or 'user'.
+ * @param $entities
+ *   The array of entity objects to add fields to, keyed by entity ID.
+ * @param $age
+ *   FIELD_LOAD_CURRENT to load the most recent revision for all fields, or
+ *   FIELD_LOAD_REVISION to load the version indicated by each entity.
+ * @param $fields
+ *   An array listing the fields to be loaded. The keys of the array are field
+ *   IDs, and the values of the array are the entity IDs (or revision IDs,
+ *   depending on the $age parameter) to add each field to.
+ * @param $options
+ *   An associative array of additional options, with the following keys:
+ *   - deleted: If TRUE, deleted fields should be loaded as well as
+ *     non-deleted fields. If unset or FALSE, only non-deleted fields should be
+ *     loaded.
+ */
+function hook_field_storage_load($entity_type, $entities, $age, $fields, $options) {
+  $load_current = $age == FIELD_LOAD_CURRENT;
+
+  foreach ($fields as $field_id => $ids) {
+    // By the time this hook runs, the relevant field definitions have been
+    // populated and cached in FieldInfo, so calling field_info_field_by_id()
+    // on each field individually is more efficient than loading all fields in
+    // memory upfront with field_info_field_by_ids().
+    $field = field_info_field_by_id($field_id);
+    $field_name = $field['field_name'];
+    $table = $load_current ? _field_sql_storage_tablename($field) : _field_sql_storage_revision_tablename($field);
+
+    $query = db_select($table, 't')
+      ->fields('t')
+      ->condition('entity_type', $entity_type)
+      ->condition($load_current ? 'entity_id' : 'revision_id', $ids, 'IN')
+      ->condition('language', field_available_languages($entity_type, $field), 'IN')
+      ->orderBy('delta');
+
+    if (empty($options['deleted'])) {
+      $query->condition('deleted', 0);
+    }
+
+    $results = $query->execute();
+
+    $delta_count = array();
+    foreach ($results as $row) {
+      if (!isset($delta_count[$row->entity_id][$row->language])) {
+        $delta_count[$row->entity_id][$row->language] = 0;
+      }
+
+      if ($field['cardinality'] == FIELD_CARDINALITY_UNLIMITED || $delta_count[$row->entity_id][$row->language] < $field['cardinality']) {
+        $item = array();
+        // For each column declared by the field, populate the item
+        // from the prefixed database column.
+        foreach ($field['columns'] as $column => $attributes) {
+          $column_name = _field_sql_storage_columnname($field_name, $column);
+          $item[$column] = $row->$column_name;
+        }
+
+        // Add the item to the field values for the entity.
+        $entities[$row->entity_id]->{$field_name}[$row->language][] = $item;
+        $delta_count[$row->entity_id][$row->language]++;
+      }
+    }
+  }
+}
+
+/**
+ * Write field data for an entity.
+ *
+ * This hook is invoked from field_attach_insert() and field_attach_update(),
+ * to ask the field storage module to save field data.
+ *
+ * @param $entity_type
+ *   The entity type of entity, such as 'node' or 'user'.
+ * @param $entity
+ *   The entity on which to operate.
+ * @param $op
+ *   FIELD_STORAGE_UPDATE when updating an existing entity,
+ *   FIELD_STORAGE_INSERT when inserting a new entity.
+ * @param $fields
+ *   An array listing the fields to be written. The keys and values of the
+ *   array are field IDs.
+ */
+function hook_field_storage_write($entity_type, $entity, $op, $fields) {
+  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
+  if (!isset($vid)) {
+    $vid = $id;
+  }
+
+  foreach ($fields as $field_id) {
+    $field = field_info_field_by_id($field_id);
+    $field_name = $field['field_name'];
+    $table_name = _field_sql_storage_tablename($field);
+    $revision_name = _field_sql_storage_revision_tablename($field);
+
+    $all_languages = field_available_languages($entity_type, $field);
+    $field_languages = array_intersect($all_languages, array_keys((array) $entity->$field_name));
+
+    // Delete and insert, rather than update, in case a value was added.
+    if ($op == FIELD_STORAGE_UPDATE) {
+      // Delete languages present in the incoming $entity->$field_name.
+      // Delete all languages if $entity->$field_name is empty.
+      $languages = !empty($entity->$field_name) ? $field_languages : $all_languages;
+      if ($languages) {
+        db_delete($table_name)
+          ->condition('entity_type', $entity_type)
+          ->condition('entity_id', $id)
+          ->condition('language', $languages, 'IN')
+          ->execute();
+        db_delete($revision_name)
+          ->condition('entity_type', $entity_type)
+          ->condition('entity_id', $id)
+          ->condition('revision_id', $vid)
+          ->condition('language', $languages, 'IN')
+          ->execute();
+      }
+    }
+
+    // Prepare the multi-insert query.
+    $do_insert = FALSE;
+    $columns = array('entity_type', 'entity_id', 'revision_id', 'bundle', 'delta', 'language');
+    foreach ($field['columns'] as $column => $attributes) {
+      $columns[] = _field_sql_storage_columnname($field_name, $column);
+    }
+    $query = db_insert($table_name)->fields($columns);
+    $revision_query = db_insert($revision_name)->fields($columns);
+
+    foreach ($field_languages as $langcode) {
+      $items = (array) $entity->{$field_name}[$langcode];
+      $delta_count = 0;
+      foreach ($items as $delta => $item) {
+        // We now know we have someting to insert.
+        $do_insert = TRUE;
+        $record = array(
+          'entity_type' => $entity_type,
+          'entity_id' => $id,
+          'revision_id' => $vid,
+          'bundle' => $bundle,
+          'delta' => $delta,
+          'language' => $langcode,
+        );
+        foreach ($field['columns'] as $column => $attributes) {
+          $record[_field_sql_storage_columnname($field_name, $column)] = isset($item[$column]) ? $item[$column] : NULL;
+        }
+        $query->values($record);
+        if (isset($vid)) {
+          $revision_query->values($record);
+        }
+
+        if ($field['cardinality'] != FIELD_CARDINALITY_UNLIMITED && ++$delta_count == $field['cardinality']) {
+          break;
+        }
+      }
+    }
+
+    // Execute the query if we have values to insert.
+    if ($do_insert) {
+      $query->execute();
+      $revision_query->execute();
+    }
+  }
+}
+
+/**
+ * Delete all field data for an entity.
+ *
+ * This hook is invoked from field_attach_delete() to ask the field storage
+ * module to delete field data.
+ *
+ * @param $entity_type
+ *   The entity type of entity, such as 'node' or 'user'.
+ * @param $entity
+ *   The entity on which to operate.
+ * @param $fields
+ *   An array listing the fields to delete. The keys and values of the
+ *   array are field IDs.
+ */
+function hook_field_storage_delete($entity_type, $entity, $fields) {
+  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
+
+  foreach (field_info_instances($entity_type, $bundle) as $instance) {
+    if (isset($fields[$instance['field_id']])) {
+      $field = field_info_field_by_id($instance['field_id']);
+      field_sql_storage_field_storage_purge($entity_type, $entity, $field, $instance);
+    }
+  }
+}
+
+/**
+ * Delete a single revision of field data for an entity.
+ *
+ * This hook is invoked from field_attach_delete_revision() to ask the field
+ * storage module to delete field revision data.
+ *
+ * Deleting the current (most recently written) revision is not
+ * allowed as has undefined results.
+ *
+ * @param $entity_type
+ *   The entity type of entity, such as 'node' or 'user'.
+ * @param $entity
+ *   The entity on which to operate. The revision to delete is
+ *   indicated by the entity's revision ID property, as identified by
+ *   hook_fieldable_info() for $entity_type.
+ * @param $fields
+ *   An array listing the fields to delete. The keys and values of the
+ *   array are field IDs.
+ */
+function hook_field_storage_delete_revision($entity_type, $entity, $fields) {
+  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
+
+  if (isset($vid)) {
+    foreach ($fields as $field_id) {
+      $field = field_info_field_by_id($field_id);
+      $revision_name = _field_sql_storage_revision_tablename($field);
+      db_delete($revision_name)
+        ->condition('entity_type', $entity_type)
+        ->condition('entity_id', $id)
+        ->condition('revision_id', $vid)
+        ->execute();
+    }
+  }
+}
+
+/**
+ * Execute an EntityFieldQuery.
+ *
+ * This hook is called to find the entities having certain entity and field
+ * conditions and sort them in the given field order. If the field storage
+ * engine also handles property sorts and orders, it should unset those
+ * properties in the called object to signal that those have been handled.
+ *
+ * @param EntityFieldQuery $query
+ *   An EntityFieldQuery.
+ *
+ * @return
+ *   See EntityFieldQuery::execute() for the return values.
+ */
+function hook_field_storage_query($query) {
+  $groups = array();
+  if ($query->age == FIELD_LOAD_CURRENT) {
+    $tablename_function = '_field_sql_storage_tablename';
+    $id_key = 'entity_id';
+  }
+  else {
+    $tablename_function = '_field_sql_storage_revision_tablename';
+    $id_key = 'revision_id';
+  }
+  $table_aliases = array();
+  // Add tables for the fields used.
+  foreach ($query->fields as $key => $field) {
+    $tablename = $tablename_function($field);
+    // Every field needs a new table.
+    $table_alias = $tablename . $key;
+    $table_aliases[$key] = $table_alias;
+    if ($key) {
+      $select_query->join($tablename, $table_alias, "$table_alias.entity_type = $field_base_table.entity_type AND $table_alias.$id_key = $field_base_table.$id_key");
+    }
+    else {
+      $select_query = db_select($tablename, $table_alias);
+      $select_query->addTag('entity_field_access');
+      $select_query->addMetaData('base_table', $tablename);
+      $select_query->fields($table_alias, array('entity_type', 'entity_id', 'revision_id', 'bundle'));
+      $field_base_table = $table_alias;
+    }
+    if ($field['cardinality'] != 1) {
+      $select_query->distinct();
+    }
+  }
+
+  // Add field conditions.
+  foreach ($query->fieldConditions as $key => $condition) {
+    $table_alias = $table_aliases[$key];
+    $field = $condition['field'];
+    // Add the specified condition.
+    $sql_field = "$table_alias." . _field_sql_storage_columnname($field['field_name'], $condition['column']);
+    $query->addCondition($select_query, $sql_field, $condition);
+    // Add delta / language group conditions.
+    foreach (array('delta', 'language') as $column) {
+      if (isset($condition[$column . '_group'])) {
+        $group_name = $condition[$column . '_group'];
+        if (!isset($groups[$column][$group_name])) {
+          $groups[$column][$group_name] = $table_alias;
+        }
+        else {
+          $select_query->where("$table_alias.$column = " . $groups[$column][$group_name] . ".$column");
+        }
+      }
+    }
+  }
+
+  if (isset($query->deleted)) {
+    $select_query->condition("$field_base_table.deleted", (int) $query->deleted);
+  }
+
+  // Is there a need to sort the query by property?
+  $has_property_order = FALSE;
+  foreach ($query->order as $order) {
+    if ($order['type'] == 'property') {
+      $has_property_order = TRUE;
+    }
+  }
+
+  if ($query->propertyConditions || $has_property_order) {
+    if (empty($query->entityConditions['entity_type']['value'])) {
+      throw new EntityFieldQueryException('Property conditions and orders must have an entity type defined.');
+    }
+    $entity_type = $query->entityConditions['entity_type']['value'];
+    $entity_base_table = _field_sql_storage_query_join_entity($select_query, $entity_type, $field_base_table);
+    $query->entityConditions['entity_type']['operator'] = '=';
+    foreach ($query->propertyConditions as $property_condition) {
+      $query->addCondition($select_query, "$entity_base_table." . $property_condition['column'], $property_condition);
+    }
+  }
+  foreach ($query->entityConditions as $key => $condition) {
+    $query->addCondition($select_query, "$field_base_table.$key", $condition);
+  }
+
+  // Order the query.
+  foreach ($query->order as $order) {
+    if ($order['type'] == 'entity') {
+      $key = $order['specifier'];
+      $select_query->orderBy("$field_base_table.$key", $order['direction']);
+    }
+    elseif ($order['type'] == 'field') {
+      $specifier = $order['specifier'];
+      $field = $specifier['field'];
+      $table_alias = $table_aliases[$specifier['index']];
+      $sql_field = "$table_alias." . _field_sql_storage_columnname($field['field_name'], $specifier['column']);
+      $select_query->orderBy($sql_field, $order['direction']);
+    }
+    elseif ($order['type'] == 'property') {
+      $select_query->orderBy("$entity_base_table." . $order['specifier'], $order['direction']);
+    }
+  }
+
+  return $query->finishQuery($select_query, $id_key);
+}
+
+/**
+ * Act on creation of a new field.
+ *
+ * This hook is invoked from field_create_field() to ask the field storage
+ * module to save field information and prepare for storing field instances.
+ * If there is a problem, the field storage module should throw an exception.
+ *
+ * @param $field
+ *   The field structure being created.
+ */
+function hook_field_storage_create_field($field) {
+  $schema = _field_sql_storage_schema($field);
+  foreach ($schema as $name => $table) {
+    db_create_table($name, $table);
+  }
+  drupal_get_schema(NULL, TRUE);
+}
+
+/**
+ * Act on deletion of a field.
+ *
+ * This hook is invoked from field_delete_field() to ask the field storage
+ * module to mark all information stored in the field for deletion.
+ *
+ * @param $field
+ *   The field being deleted.
+ */
+function hook_field_storage_delete_field($field) {
+  // Mark all data associated with the field for deletion.
+  $field['deleted'] = 0;
+  $table = _field_sql_storage_tablename($field);
+  $revision_table = _field_sql_storage_revision_tablename($field);
+  db_update($table)
+    ->fields(array('deleted' => 1))
+    ->execute();
+
+  // Move the table to a unique name while the table contents are being deleted.
+  $field['deleted'] = 1;
+  $new_table = _field_sql_storage_tablename($field);
+  $revision_new_table = _field_sql_storage_revision_tablename($field);
+  db_rename_table($table, $new_table);
+  db_rename_table($revision_table, $revision_new_table);
+  drupal_get_schema(NULL, TRUE);
+}
+
+/**
+ * Act on deletion of a field instance.
+ *
+ * This hook is invoked from field_delete_instance() to ask the field storage
+ * module to mark all information stored for the field instance for deletion.
+ *
+ * @param $instance
+ *   The instance being deleted.
+ */
+function hook_field_storage_delete_instance($instance) {
+  $field = field_info_field($instance['field_name']);
+  $table_name = _field_sql_storage_tablename($field);
+  $revision_name = _field_sql_storage_revision_tablename($field);
+  db_update($table_name)
+    ->fields(array('deleted' => 1))
+    ->condition('entity_type', $instance['entity_type'])
+    ->condition('bundle', $instance['bundle'])
+    ->execute();
+  db_update($revision_name)
+    ->fields(array('deleted' => 1))
+    ->condition('entity_type', $instance['entity_type'])
+    ->condition('bundle', $instance['bundle'])
+    ->execute();
+}
+
+/**
+ * Act before the storage backends load field data.
+ *
+ * This hook allows modules to load data before the Field Storage API,
+ * optionally preventing the field storage module from doing so.
+ *
+ * This lets 3rd party modules override, mirror, shard, or otherwise store a
+ * subset of fields in a different way than the current storage engine.
+ * Possible use cases include per-bundle storage, per-combo-field storage, etc.
+ *
+ * Modules implementing this hook should load field values and add them to
+ * objects in $entities. Fields with no values should be added as empty
+ * arrays. In addition, fields loaded should be added as keys to $skip_fields.
+ *
+ * @param $entity_type
+ *   The type of entity, such as 'node' or 'user'.
+ * @param $entities
+ *   The array of entity objects to add fields to, keyed by entity ID.
+ * @param $age
+ *   FIELD_LOAD_CURRENT to load the most recent revision for all fields, or
+ *   FIELD_LOAD_REVISION to load the version indicated by each entity.
+ * @param $skip_fields
+ *   An array keyed by field IDs whose data has already been loaded and
+ *   therefore should not be loaded again. Add a key to this array to indicate
+ *   that your module has already loaded a field.
+ * @param $options
+ *   An associative array of additional options, with the following keys:
+ *   - field_id: The field ID that should be loaded. If unset, all fields
+ *     should be loaded.
+ *   - deleted: If TRUE, deleted fields should be loaded as well as
+ *     non-deleted fields. If unset or FALSE, only non-deleted fields should be
+ *     loaded.
+ */
+function hook_field_storage_pre_load($entity_type, $entities, $age, &$skip_fields, $options) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act before the storage backends insert field data.
+ *
+ * This hook allows modules to store data before the Field Storage API,
+ * optionally preventing the field storage module from doing so.
+ *
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   The entity with fields to save.
+ * @param $skip_fields
+ *   An array keyed by field IDs whose data has already been written and
+ *   therefore should not be written again. The values associated with these
+ *   keys are not specified.
+ * @return
+ *   Saved field IDs are set set as keys in $skip_fields.
+ */
+function hook_field_storage_pre_insert($entity_type, $entity, &$skip_fields) {
+  if ($entity_type == 'node' && $entity->status && _forum_node_check_node_type($entity)) {
+    $query = db_insert('forum_index')->fields(array('nid', 'title', 'tid', 'sticky', 'created', 'comment_count', 'last_comment_timestamp'));
+    foreach ($entity->taxonomy_forums as $language) {
+      foreach ($language as $delta) {
+        $query->values(array(
+          'nid' => $entity->nid,
+          'title' => $entity->title,
+          'tid' => $delta['value'],
+          'sticky' => $entity->sticky,
+          'created' => $entity->created,
+          'comment_count' => 0,
+          'last_comment_timestamp' => $entity->created,
+        ));
+      }
+    }
+    $query->execute();
+  }
+}
+
+/**
+ * Act before the storage backends update field data.
+ *
+ * This hook allows modules to store data before the Field Storage API,
+ * optionally preventing the field storage module from doing so.
+ *
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   The entity with fields to save.
+ * @param $skip_fields
+ *   An array keyed by field IDs whose data has already been written and
+ *   therefore should not be written again. The values associated with these
+ *   keys are not specified.
+ * @return
+ *   Saved field IDs are set set as keys in $skip_fields.
+ */
+function hook_field_storage_pre_update($entity_type, $entity, &$skip_fields) {
+  $first_call = &drupal_static(__FUNCTION__, array());
+
+  if ($entity_type == 'node' && $entity->status && _forum_node_check_node_type($entity)) {
+    // We don't maintain data for old revisions, so clear all previous values
+    // from the table. Since this hook runs once per field, per entity, make
+    // sure we only wipe values once.
+    if (!isset($first_call[$entity->nid])) {
+      $first_call[$entity->nid] = FALSE;
+      db_delete('forum_index')->condition('nid', $entity->nid)->execute();
+    }
+    // Only save data to the table if the node is published.
+    if ($entity->status) {
+      $query = db_insert('forum_index')->fields(array('nid', 'title', 'tid', 'sticky', 'created', 'comment_count', 'last_comment_timestamp'));
+      foreach ($entity->taxonomy_forums as $language) {
+        foreach ($language as $delta) {
+          $query->values(array(
+            'nid' => $entity->nid,
+            'title' => $entity->title,
+            'tid' => $delta['value'],
+            'sticky' => $entity->sticky,
+            'created' => $entity->created,
+            'comment_count' => 0,
+            'last_comment_timestamp' => $entity->created,
+          ));
+        }
+      }
+      $query->execute();
+      // The logic for determining last_comment_count is fairly complex, so
+      // call _forum_update_forum_index() too.
+      _forum_update_forum_index($entity->nid);
+    }
+  }
+}
+
+/**
+ * Returns the maximum weight for the entity components handled by the module.
+ *
+ * Field API takes care of fields and 'extra_fields'. This hook is intended for
+ * third-party modules adding other entity components (e.g. field_group).
+ *
+ * @param $entity_type
+ *   The type of entity; e.g. 'node' or 'user'.
+ * @param $bundle
+ *   The bundle name.
+ * @param $context
+ *   The context for which the maximum weight is requested. Either 'form', or
+ *   the name of a view mode.
+ * @return
+ *   The maximum weight of the entity's components, or NULL if no components
+ *   were found.
+ */
+function hook_field_info_max_weight($entity_type, $bundle, $context) {
+  $weights = array();
+
+  foreach (my_module_entity_additions($entity_type, $bundle, $context) as $addition) {
+    $weights[] = $addition['weight'];
+  }
+
+  return $weights ? max($weights) : NULL;
+}
+
+/**
+ * Alters the display settings of a field before it gets displayed.
+ *
+ * Note that instead of hook_field_display_alter(), which is called for all
+ * fields on all entity types, hook_field_display_ENTITY_TYPE_alter() may be
+ * used to alter display settings for fields on a specific entity type only.
+ *
+ * This hook is called once per field per displayed entity. If the result of the
+ * hook involves reading from the database, it is highly recommended to
+ * statically cache the information.
+ *
+ * @param $display
+ *   The display settings that will be used to display the field values, as
+ *   found in the 'display' key of $instance definitions.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g., 'node' or 'user'.
+ *   - field: The field being rendered.
+ *   - instance: The instance being rendered.
+ *   - entity: The entity being rendered.
+ *   - view_mode: The view mode, e.g. 'full', 'teaser'...
+ *
+ * @see hook_field_display_ENTITY_TYPE_alter()
+ */
+function hook_field_display_alter(&$display, $context) {
+  // Leave field labels out of the search index.
+  // Note: The check against $context['entity_type'] == 'node' could be avoided
+  // by using hook_field_display_node_alter() instead of
+  // hook_field_display_alter(), resulting in less function calls when
+  // rendering non-node entities.
+  if ($context['entity_type'] == 'node' && $context['view_mode'] == 'search_index') {
+    $display['label'] = 'hidden';
+  }
+}
+
+/**
+ * Alters the display settings of a field on a given entity type before it gets displayed.
+ *
+ * Modules can implement hook_field_display_ENTITY_TYPE_alter() to alter display
+ * settings for fields on a specific entity type, rather than implementing
+ * hook_field_display_alter().
+ *
+ * This hook is called once per field per displayed entity. If the result of the
+ * hook involves reading from the database, it is highly recommended to
+ * statically cache the information.
+ *
+ * @param $display
+ *   The display settings that will be used to display the field values, as
+ *   found in the 'display' key of $instance definitions.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g., 'node' or 'user'.
+ *   - field: The field being rendered.
+ *   - instance: The instance being rendered.
+ *   - entity: The entity being rendered.
+ *   - view_mode: The view mode, e.g. 'full', 'teaser'...
+ *
+ * @see hook_field_display_alter()
+ */
+function hook_field_display_ENTITY_TYPE_alter(&$display, $context) {
+  // Leave field labels out of the search index.
+  if ($context['view_mode'] == 'search_index') {
+    $display['label'] = 'hidden';
+  }
+}
+
+/**
+ * Alters the display settings of pseudo-fields before an entity is displayed.
+ *
+ * This hook is called once per displayed entity. If the result of the hook
+ * involves reading from the database, it is highly recommended to statically
+ * cache the information.
+ *
+ * @param $displays
+ *   An array of display settings for the pseudo-fields in the entity, keyed
+ *   by pseudo-field names.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g., 'node' or 'user'.
+ *   - bundle: The bundle name.
+ *   - view_mode: The view mode, e.g. 'full', 'teaser'...
+ */
+function hook_field_extra_fields_display_alter(&$displays, $context) {
+  if ($context['entity_type'] == 'taxonomy_term' && $context['view_mode'] == 'full') {
+    $displays['description']['visible'] = FALSE;
+  }
+}
+
+/**
+ * Alters the widget properties of a field instance on a given entity type
+ * before it gets displayed.
+ *
+ * Modules can implement hook_field_widget_properties_ENTITY_TYPE_alter() to
+ * alter the widget properties for fields on a specific entity type, rather than
+ * implementing hook_field_widget_properties_alter().
+ *
+ * This hook is called once per field per displayed widget entity. If the result
+ * of the hook involves reading from the database, it is highly recommended to
+ * statically cache the information.
+ *
+ * @param $widget
+ *   The instance's widget properties.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g., 'node' or 'user'.
+ *   - entity: The entity object.
+ *   - field: The field that the widget belongs to.
+ *   - instance: The instance of the field.
+ *
+ * @see hook_field_widget_properties_alter()
+ */
+function hook_field_widget_properties_ENTITY_TYPE_alter(&$widget, $context) {
+  // Change a widget's type according to the time of day.
+  $field = $context['field'];
+  if ($field['field_name'] == 'field_foo') {
+    $time = date('H');
+    $widget['type'] = $time < 12 ? 'widget_am' : 'widget_pm';
+  }
+}
+
+/**
+ * @} End of "addtogroup field_storage".
+ */
+
+/**
+ * @addtogroup field_crud
+ * @{
+ */
+
+/**
+ * Act on a field being created.
+ *
+ * This hook is invoked from field_create_field() after the field is created, to
+ * allow modules to act on field creation.
+ *
+ * @param $field
+ *   The field just created.
+ */
+function hook_field_create_field($field) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on a field instance being created.
+ *
+ * This hook is invoked from field_create_instance() after the instance record
+ * is saved, so it cannot be used to modify the instance itself.
+ *
+ * @param $instance
+ *   The instance just created.
+ */
+function hook_field_create_instance($instance) {
+  // @todo Needs function body.
+}
+
+/**
+ * Forbid a field update from occurring.
+ *
+ * Any module may forbid any update for any reason. For example, the
+ * field's storage module might forbid an update if it would change
+ * the storage schema while data for the field exists. A field type
+ * module might forbid an update if it would change existing data's
+ * semantics, or if there are external dependencies on field settings
+ * that cannot be updated.
+ *
+ * To forbid the update from occurring, throw a FieldUpdateForbiddenException.
+ *
+ * @param $field
+ *   The field as it will be post-update.
+ * @param $prior_field
+ *   The field as it is pre-update.
+ * @param $has_data
+ *   Whether any data already exists for this field.
+ */
+function hook_field_update_forbid($field, $prior_field, $has_data) {
+  // A 'list' field stores integer keys mapped to display values. If
+  // the new field will have fewer values, and any data exists for the
+  // abandoned keys, the field will have no way to display them. So,
+  // forbid such an update.
+  if ($has_data && count($field['settings']['allowed_values']) < count($prior_field['settings']['allowed_values'])) {
+    // Identify the keys that will be lost.
+    $lost_keys = array_diff(array_keys($field['settings']['allowed_values']), array_keys($prior_field['settings']['allowed_values']));
+    // If any data exist for those keys, forbid the update.
+    $query = new EntityFieldQuery();
+    $found = $query
+      ->fieldCondition($prior_field['field_name'], 'value', $lost_keys)
+      ->range(0, 1)
+      ->execute();
+    if ($found) {
+      throw new FieldUpdateForbiddenException("Cannot update a list field not to include keys with existing data");
+    }
+  }
+}
+
+/**
+ * Act on a field being updated.
+ *
+ * This hook is invoked just after field is updated in field_update_field().
+ *
+ * @param $field
+ *   The field as it is post-update.
+ * @param $prior_field
+ *   The field as it was pre-update.
+ * @param $has_data
+ *   Whether any data already exists for this field.
+ */
+function hook_field_update_field($field, $prior_field, $has_data) {
+  // Reset the static value that keeps track of allowed values for list fields.
+  drupal_static_reset('list_allowed_values');
+}
+
+/**
+ * Act on a field being deleted.
+ *
+ * This hook is invoked just after a field is deleted by field_delete_field().
+ *
+ * @param $field
+ *   The field just deleted.
+ */
+function hook_field_delete_field($field) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on a field instance being updated.
+ *
+ * This hook is invoked from field_update_instance() after the instance record
+ * is saved, so it cannot be used by a module to modify the instance itself.
+ *
+ * @param $instance
+ *   The instance as it is post-update.
+ * @param $prior_instance
+ *   The instance as it was pre-update.
+ */
+function hook_field_update_instance($instance, $prior_instance) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on a field instance being deleted.
+ *
+ * This hook is invoked from field_delete_instance() after the instance is
+ * deleted.
+ *
+ * @param $instance
+ *   The instance just deleted.
+ */
+function hook_field_delete_instance($instance) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on field records being read from the database.
+ *
+ * This hook is invoked from field_read_fields() on each field being read.
+ *
+ * @param $field
+ *   The field record just read from the database.
+ */
+function hook_field_read_field($field) {
+  // @todo Needs function body.
+}
+
+/**
+ * Act on a field record being read from the database.
+ *
+ * This hook is invoked from field_read_instances() on each instance being read.
+ *
+ * @param $instance
+ *   The instance record just read from the database.
+ */
+function hook_field_read_instance($instance) {
+  // @todo Needs function body.
+}
+
+/**
+ * Acts when a field record is being purged.
+ *
+ * In field_purge_field(), after the field configuration has been
+ * removed from the database, the field storage module has had a chance to
+ * run its hook_field_storage_purge_field(), and the field info cache
+ * has been cleared, this hook is invoked on all modules to allow them to
+ * respond to the field being purged.
+ *
+ * @param $field
+ *   The field being purged.
+ */
+function hook_field_purge_field($field) {
+  db_delete('my_module_field_info')
+    ->condition('id', $field['id'])
+    ->execute();
+}
+
+/**
+ * Acts when a field instance is being purged.
+ *
+ * In field_purge_instance(), after the field instance has been
+ * removed from the database, the field storage module has had a chance to
+ * run its hook_field_storage_purge_instance(), and the field info cache
+ * has been cleared, this hook is invoked on all modules to allow them to
+ * respond to the field instance being purged.
+ *
+ * @param $instance
+ *   The instance being purged.
+ */
+function hook_field_purge_instance($instance) {
+  db_delete('my_module_field_instance_info')
+    ->condition('id', $instance['id'])
+    ->execute();
+}
+
+/**
+ * Remove field storage information when a field record is purged.
+ *
+ * Called from field_purge_field() to allow the field storage module
+ * to remove field information when a field is being purged.
+ *
+ * @param $field
+ *   The field being purged.
+ */
+function hook_field_storage_purge_field($field) {
+  $table_name = _field_sql_storage_tablename($field);
+  $revision_name = _field_sql_storage_revision_tablename($field);
+  db_drop_table($table_name);
+  db_drop_table($revision_name);
+}
+
+/**
+ * Remove field storage information when a field instance is purged.
+ *
+ * Called from field_purge_instance() to allow the field storage module
+ * to remove field instance information when a field instance is being
+ * purged.
+ *
+ * @param $instance
+ *   The instance being purged.
+ */
+function hook_field_storage_purge_field_instance($instance) {
+  db_delete('my_module_field_instance_info')
+    ->condition('id', $instance['id'])
+    ->execute();
+}
+
+/**
+ * Remove field storage information when field data is purged.
+ *
+ * Called from field_purge_data() to allow the field storage
+ * module to delete field data information.
+ *
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   The pseudo-entity whose field data to delete.
+ * @param $field
+ *   The (possibly deleted) field whose data is being purged.
+ * @param $instance
+ *   The deleted field instance whose data is being purged.
+ */
+function hook_field_storage_purge($entity_type, $entity, $field, $instance) {
+  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
+
+  $table_name = _field_sql_storage_tablename($field);
+  $revision_name = _field_sql_storage_revision_tablename($field);
+  db_delete($table_name)
+    ->condition('entity_type', $entity_type)
+    ->condition('entity_id', $id)
+    ->execute();
+  db_delete($revision_name)
+    ->condition('entity_type', $entity_type)
+    ->condition('entity_id', $id)
+    ->execute();
+}
+
+/**
+ * @} End of "addtogroup field_crud".
+ */
+
+/**
+ * Determine whether the user has access to a given field.
+ *
+ * This hook is invoked from field_access() to let modules block access to
+ * operations on fields. If no module returns FALSE, the operation is allowed.
+ *
+ * @param $op
+ *   The operation to be performed. Possible values: 'edit', 'view'.
+ * @param $field
+ *   The field on which the operation is to be performed.
+ * @param $entity_type
+ *   The type of $entity; for example, 'node' or 'user'.
+ * @param $entity
+ *   (optional) The entity for the operation.
+ * @param $account
+ *   (optional) The account to check; if not given use currently logged in user.
+ *
+ * @return
+ *   TRUE if the operation is allowed, and FALSE if the operation is denied.
+ */
+function hook_field_access($op, $field, $entity_type, $entity, $account) {
+  if ($field['field_name'] == 'field_of_interest' && $op == 'edit') {
+    return user_access('edit field of interest', $account);
+  }
+  return TRUE;
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */