diff sites/all/modules/restws/restws.formats.inc @ 4:ce11bbd8f642

added modules

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sites/all/modules/restws/restws.formats.inc	Thu Sep 19 10:38:44 2013 +0100
@@ -0,0 +1,788 @@
+<?php
+
+/**
+ * @file
+ * RESTful web services module formats.
+ */
+
+/**
+ * Interface implemented by formatter implementations for the http client.
+ */
+interface RestWSFormatInterface {
+
+  /**
+   * Gets the representation of a resource.
+   *
+   * @param RestWSResourceControllerInterface $resourceController
+   *   The controller used to retrieve the resource.
+   * @param int|string $id
+   *   The id of the resource that should be returned.
+   *
+   * @return string
+   *   The representation of the resource.
+   */
+  public function viewResource($resourceController, $id);
+
+  /**
+   * Create a resource.
+   *
+   * @param RestWSResourceControllerInterface $resourceController
+   *   The controller used to create the resource.
+   * @param string $data
+   *   The representation of the resource.
+   *
+   * @return int|string
+   *   The id of the newly created resource.
+   */
+  public function createResource($resourceController, $data);
+
+  /**
+   * Update a resource.
+   *
+   * @param RestWSResourceControllerInterface $resourceController
+   *   The controller used to update the resource.
+   * @param int|string $id
+   *   The id of the resource that should be updated.
+   * @param string $data
+   *   The representation of the resource.
+   */
+  public function updateResource($resourceController, $id, $data);
+
+  /**
+   * Delete a resource.
+   *
+   * @param RestWSResourceControllerInterface $resourceController
+   *   The controller used to update the resource.
+   * @param int|string $id
+   *   The id of the resource that should be deleted.
+   */
+  public function deleteResource($resourceController, $id);
+
+  /**
+   * Query for a resource.
+   *
+   * If a format doesn't want to implement querying, then it should throw an
+   * RestWSException with the 501 HTTP status code.
+   *
+   * @param RestWSResourceControllerInterface $resourceController
+   *   The controller used to query the resource.
+   * @param array $payload
+   *   An optional way to pass the query parameters.
+   *
+   * @return string
+   *   The serialized representation of a list of resources.
+   */
+  public function queryResource($resourceController, $payload);
+
+
+  /**
+   * Returns the mime type of this format, e.g. 'application/json' or
+   * 'application/xml'.
+   */
+  public function mimeType();
+
+  /**
+   * Returns the short name of this format.
+   *
+   * @return string
+   *   The format name, example: "json".
+   */
+  public function getName();
+}
+
+/**
+ * A base for all simple formats that are just serializing/unserializing an
+ * array of property values.
+ */
+abstract class RestWSBaseFormat implements RestWSFormatInterface {
+
+  protected $formatName;
+  protected $formatInfo;
+
+  public function __construct($name, $info) {
+    $this->formatName = $name;
+    $this->formatInfo = $info;
+  }
+
+  /**
+   * Gets the representation of a resource.
+   */
+  public function viewResource($resourceController, $id) {
+    $values = self::getData($resourceController->wrapper($id));
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $values, $function, $this->formatName);
+
+    return $this->serialize($values);
+  }
+
+  /**
+   * Creates a new resource.
+   */
+  public function createResource($resourceController, $data) {
+    $values = $this->unserialize($resourceController->propertyInfo(), $data);
+    $id = $resourceController->create($values);
+    $ref = self::getResourceReference($resourceController->resource(), $id);
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $ref, $function, $this->formatName);
+
+    return $this->serialize($ref);
+  }
+
+  /**
+   * Updates a resource.
+   */
+  public function updateResource($resourceController, $id, $data) {
+    $values = $this->unserialize($resourceController->propertyInfo(), $data);
+    $resourceController->update($id, $values);
+    // Return an empty representation by default.
+    $value = array();
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $value, $function, $this->formatName);
+
+    return $this->serialize($value);
+  }
+
+  /**
+   * Deletes a resource.
+   */
+  public function deleteResource($resourceController, $id) {
+    $resourceController->delete($id);
+    // Return an empty representation by default.
+    $value = array();
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $value, $function, $this->formatName);
+
+    return $this->serialize($value);
+  }
+
+  /**
+   * Implements RestWSFormatInterface::queryResource().
+   */
+  public function queryResource($resourceController, $payload) {
+    // Get the parameter from the URL.
+    $parameters = drupal_get_query_parameters();
+
+    $rest_controls = restws_meta_controls();
+    $properties = $resourceController->propertyInfo();
+    $split_parameters = $this->splitParameters($properties, $parameters);
+
+    $values = $this->generateQueryURIs($resourceController, $parameters, $split_parameters['filters']);
+
+    $full = (isset($split_parameters['meta_controls'][$rest_controls['full']])) ? $split_parameters['meta_controls'][$rest_controls['full']] : 1;
+
+    $result = $resourceController->query($split_parameters['filters'], $split_parameters['meta_controls']);
+    if ($full === '0') {
+      foreach ($result as $id) {
+        $values['list'][] = $this->getResourceReference($resourceController->resource(), $id);
+      }
+    }
+    else {
+      foreach ($result as $id) {
+        $values['list'][] = self::getData($resourceController->wrapper($id));
+      }
+    }
+
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $values, $function, $this->formatName);
+
+    return $this->serialize($values);
+  }
+
+  public function mimeType() {
+    return $this->formatInfo['mime type'];
+  }
+
+  public function getName() {
+    return $this->formatName;
+  }
+
+  /**
+   * Gets a simple PHP array using URI references for some wrapped data.
+   *
+   * This is the counter-part of self::getPropertyValues().
+   */
+  public static function getData($wrapper) {
+    $data = array();
+    $filtered = restws_property_access_filter($wrapper);
+    foreach ($filtered as $name => $property) {
+      try {
+        if ($property instanceof EntityDrupalWrapper) {
+          // For referenced entities only return the URI.
+          if ($id = $property->getIdentifier()) {
+            $data[$name] = self::getResourceReference($property->type(), $id);
+          }
+        }
+        elseif ($property instanceof EntityValueWrapper) {
+          $data[$name] = $property->value();
+        }
+        elseif ($property instanceof EntityListWrapper || $property instanceof EntityStructureWrapper) {
+          $data[$name] = self::getData($property);
+        }
+      }
+      catch (EntityMetadataWrapperException $e) {
+        // A property causes problems - ignore that.
+      }
+    }
+    return $data;
+  }
+
+  public static function getResourceReference($resource, $id) {
+    $return = array(
+      'uri' => restws_resource_uri($resource, $id),
+      'id' => $id,
+      'resource' => $resource,
+    );
+    if (module_exists('uuid') && entity_get_info($resource)) {
+      $ids = entity_get_uuid_by_id($resource, array($id));
+      if ($id = reset($ids)) {
+        $return['uuid'] = $id;
+      }
+    }
+    return $return;
+  }
+
+  /**
+   * Transforms simple-array data values to valid entity property values.
+   *
+   * This is the counter-part of self::getData(), thus it converts resource
+   * references to the required value(s).
+   *
+   * @param array $values
+   *   The array representation of the data values.
+   * @param $property_info
+   *   The property info array of the entity type for which we are transforming
+   *   the values.
+   */
+  protected function getPropertyValues(array &$values, $property_info) {
+    foreach ($values as $name => &$property_value) {
+      if (isset($property_info[$name]) && $info = $property_info[$name]) {
+
+        // Check if there is a resource array and if the property has a type.
+        if (is_array($property_value) && isset($info['type'])) {
+
+          // Check if the field is a list or a single value field.
+          if (entity_property_list_extract_type($info['type'])) {
+            // Check if the list values consist of structure wrappers.
+            if (array_key_exists('property info', $info)) {
+              foreach ($property_value as &$list_values) {
+                $this->getPropertyValues($list_values, $info['property info']);
+              }
+            }
+            else {
+              $list_type = entity_property_list_extract_type($info['type']);
+              foreach ($property_value as &$list_value) {
+                $list_value = $this->getResourceReferenceValue($list_type, $list_value);
+              }
+            }
+          }
+          else {
+            // Check if the property is a structure wrapper.
+            if (array_key_exists('property info', $info)) {
+              $this->getPropertyValues($property_value, $info['property info']);
+            }
+            else {
+              $property_value = $this->getResourceReferenceValue($info['type'], $property_value);
+            }
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * Gets the resource reference value.
+   *
+   * @param $type
+   *   The data type of the reference property.
+   * @param array $reference
+   *   The input data specifying the resource reference in one supported way.
+   *
+   * @return mixed
+   *   The value to be set for the reference. Usually this is an entity or
+   *   resource id, but for generic entity references it's an
+   *   EntityDrupalWrapper.
+   *
+   * @see RestWSBaseFormat::getResourceReference()
+   */
+  protected function getResourceReferenceValue($type, array $reference) {
+
+    if (isset($reference['id']) && $type != 'entity') {
+      return $reference['id'];
+    }
+    // Handle setting generic entity references, i.e. of type entity.
+    elseif ($type == 'entity' && isset($reference['id']) && isset($reference['resource'])) {
+      if (!entity_get_info($reference['resource'])) {
+        throw new RestWSException('Invalid resource for entity reference given.', 406);
+      }
+      return entity_metadata_wrapper($reference['resource'], $reference['id']);
+    }
+    elseif (isset($reference['uri'])) {
+      // @todo: Implement setting references by URI by parsing resource/id from
+      // the URI.
+    }
+    elseif (isset($reference['uuid']) && module_exists('uuid') && $type != 'entity') {
+      $ids = entity_get_id_by_uuid($type, array($reference['uuid']));
+      if (!$ids) {
+        throw new RestWSException('Invalid UUID for resource reference given.', 406);
+      }
+      return reset($ids);
+    }
+
+    throw new RestWSException('Invalid value for resource reference given.', 406);
+  }
+
+  /**
+   * Splits a query parameter into two sub arrays containing the filters and
+   * meta controls.
+   *
+   * @param array $properties
+   *   An array containing the properties of the resource.
+   *
+   * @param array $parameters
+   *   An array which contains filters and meta controls.
+   *
+   * @return array
+   *   An array containing two sub arrays, one for filters and one for meta
+   *   controls with corresponding keys.
+   *
+   * @throws RestWSException
+   *   If a filter isn't valid, the function will throw a RestWSException with
+   *   the 412 HTTP status code.
+   */
+  protected function splitParameters($properties, array $parameters) {
+    $meta_controls = array();
+    $rest_controls = restws_meta_controls();
+    foreach ($parameters as $control_name => $property) {
+      if (isset($rest_controls[$control_name])) {
+        $meta_controls[$control_name] = $property;
+        unset($parameters[$control_name]);
+      }
+    }
+
+    $filters = array();
+    foreach ($parameters as $parameter => $value) {
+      // Check if the property is prefixed.
+      if (substr($parameter, 0, 9) == 'property_') {
+        $parameter = substr($parameter, 9, strlen($parameter) - 9);
+      }
+
+      // If the parameter doesn't exist, we can not filter for and need to
+      // notify the client about it.
+      if (!isset($properties[$parameter])) {
+        throw new RestWSException('Not a valid filter: ' . $parameter, 412);
+      }
+      $filters[$parameter] = $value;
+    }
+    return array('meta_controls' => $meta_controls, 'filters' => $filters);
+  }
+
+  /**
+   * Generates all navigation links for querying.
+   *
+   * @param RestWSResourceControllerInterface $resourceController
+   *   The controller used to query the resource.
+   *
+   * @param array $parameters
+   *   The HTTP GET parameters for the query.
+   *
+   * @param array $filters
+   *   The filters for the query.
+   *
+   * @return array
+   *   An array containing all navigation links.
+   *
+   * @throws RestWSException
+   *   If the page is out of range the function will throw a new RestWSException
+   *   with HTTP status code 404.
+   */
+  protected function generateQueryURIs(RestWSResourceControllerInterface $resourceController, array $parameters, array $filters) {
+    $rest_controls = restws_meta_controls();
+
+    $count = $resourceController->count($filters);
+    $limit = isset($parameters[$rest_controls['limit']]) ? $parameters[$rest_controls['limit']] : NULL;
+    $limit = $resourceController->limit($limit);
+    $page = isset($parameters[$rest_controls['page']]) ? $parameters[$rest_controls['page']] : 0;
+
+    $last = ceil($count / $limit) - 1;
+
+    if ($page > $last || $page < 0) {
+      throw new RestWSException('Page doesn\'t exist.', 404);
+    }
+
+    $uris = array();
+    $options = array(
+      'query' => &$parameters,
+    );
+
+    $uris['self'] = restws_resource_uri($resourceController->resource(), null, $options);
+    $parameters['page'] = 0;
+    $uris['first'] = restws_resource_uri($resourceController->resource(), null, $options);
+    $parameters['page'] = $last;
+    $uris['last'] = restws_resource_uri($resourceController->resource(), null, $options);
+
+
+    if ($page != 0) {
+      $parameters['page'] = $page - 1;
+      $uris['prev'] = restws_resource_uri($resourceController->resource(), null, $options);
+    }
+
+    if ($page != $last) {
+      $parameters['page'] = $page + 1;
+      $uris['next'] = restws_resource_uri($resourceController->resource(), null, $options);
+    }
+
+    return $uris;
+  }
+}
+
+/**
+ * Filters out properties where view access is not allowed for the current user.
+ *
+ * @param EntityMetadataWrapper $wrapper
+ *   EntityMetadataWrapper that should be checked.
+ *
+ * @return
+ *   An array of properties where access is allowed, keyed by their property
+ *   name.
+ */
+function restws_property_access_filter($wrapper) {
+  $filtered = array();
+  foreach ($wrapper as $name => $property) {
+    if ($property->access('view')) {
+      $filtered[$name] = $property;
+    }
+  }
+  return $filtered;
+}
+
+/**
+ * A formatter to format json.
+ */
+class RestWSFormatJSON extends RestWSBaseFormat {
+
+  public function serialize($values) {
+    return drupal_json_encode($values);
+  }
+
+  public function unserialize($properties, $data) {
+    $values = drupal_json_decode($data);
+    $this->getPropertyValues($values, $properties);
+    return $values;
+  }
+}
+
+/**
+ * A formatter for XML.
+ */
+class RestWSFormatXML extends RestWSBaseFormat {
+
+  /**
+   * Gets the representation of a resource.
+   */
+  public function viewResource($resourceController, $id) {
+    $xml = new DOMDocument('1.0', 'utf-8');
+    $element = $xml->createElement($resourceController->resource());
+    self::addToXML($xml, $element, $resourceController->wrapper($id));
+    $xml->appendChild($element);
+
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $xml, $function, $this->formatName);
+
+    return $xml->saveXML();
+  }
+
+  /**
+   * Creates a new resource.
+   */
+  public function createResource($resourceController, $data) {
+    $values = $this->unserialize($resourceController->propertyInfo(), $data);
+    $id = $resourceController->create($values);
+
+    $xml = new DOMDocument('1.0', 'utf-8');
+    $element = $xml->createElement('uri');
+    self::setXMLReference($element, $resourceController->resource(), $id);
+    $xml->appendChild($element);
+
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $xml, $function, $this->formatName);
+
+    return $xml->saveXML();
+  }
+
+  /**
+   * Overrides RestWSBaseFormat::queryResource().
+   */
+  public function queryResource($resourceController, $payload) {
+    $xml = new DOMDocument('1.0', 'utf-8');
+    $element = $xml->createElement('list');
+
+    $rest_controls = restws_meta_controls();
+    $parameters = drupal_get_query_parameters();
+    $properties = $resourceController->propertyInfo();
+    $split_parameters = $this->splitParameters($properties, $parameters);
+
+    $links = $this->generateQueryURIs($resourceController, $parameters, $split_parameters['filters']);
+
+    foreach ($links as $rel => $link) {
+      $item = $xml->createElement('link');
+      $item->setAttribute('rel', $rel);
+      $item->setAttribute('href', $link);
+      $element->appendChild($item);
+    }
+
+    $full = (isset($split_parameters['meta_controls'][$rest_controls['full']])) ? $split_parameters['meta_controls'][$rest_controls['full']] : 1;
+
+    $result = $resourceController->query($split_parameters['filters'], $split_parameters['meta_controls']);
+
+    if ($full === '0') {
+      foreach ($result as $id) {
+        $item = $xml->createElement($resourceController->resource());
+        self::setXMLReference($item, $resourceController->resource(), $id);
+        $element->appendChild($item);
+      }
+    }
+    else {
+      foreach ($result as $id) {
+        $item = $xml->createElement($resourceController->resource());
+        self::addToXML($xml, $item, $resourceController->wrapper($id));
+        $element->appendChild($item);
+      }
+    }
+
+    $xml->appendChild($element);
+
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $xml, $function, $this->formatName);
+
+    return $xml->saveXML();
+  }
+
+  public function serialize($data) {
+    // Return an empty XML document.
+    $xml = new DOMDocument('1.0', 'utf-8');
+    return $xml->saveXML();
+  }
+
+  public function unserialize($properties, $data) {
+    $xml = simplexml_load_string($data);
+    return $this->xmlToArray($properties, $xml);
+  }
+
+  /**
+   * Turns the xml structure into an array of values.
+   */
+  public function xmlToArray($properties, SimpleXMLElement $xml, $listItemType = NULL) {
+    foreach ($xml->children() as $name => $element) {
+      // Check if we are processing an entity, an item from a list or a list.
+      if ((isset($properties[$name]['type']) && (entity_property_list_extract_type($properties[$name]['type']) || entity_get_info($properties[$name]['type'])))  || isset($listItemType)) {
+        // If we are processing a list, then set the type of the list and save
+        // the results into a a numeric array.
+        if (isset($listItemType)) {
+          $type = $listItemType;
+          $result_pointer = &$result[];
+        }
+        else {
+          $type = $properties[$name]['type'];
+          $result_pointer = &$result[$name];
+        }
+
+        // Check if the type is a list.
+        if (entity_property_list_extract_type($type)) {
+          $result_pointer = $this->xmlToArray($properties, $element, entity_property_list_extract_type($type));
+        }
+        else {
+          $attributes = $element->attributes();
+          $values['id'] = (string)$attributes['id'];
+          $values['resource'] = (string)$attributes['resource'];
+          $values['uri'] = $this->xmlToArray($properties, $element);
+          $id = $this->getResourceReferenceValue($type, $values);
+          // If an id could be extracted, then a resource array was send.
+          if ($id !== FALSE) {
+            $result_pointer = $id;
+          }
+          else {
+            // If no ID could be extracted, then save the inner text content of
+            // the node, which is saved in the $values['uri'].
+            $result_pointer = $values['uri'];
+          }
+        }
+      }
+      else {
+        $result[$name] = $this->xmlToArray($properties, $element);
+      }
+      foreach ($xml->attributes() as $attribute_name => $attribute_value) {
+        $result[$attribute_name] = $attribute_value;
+      }
+    }
+    if (!isset($result)) {
+      $result = ($string = (string) $xml) ? $string : NULL;
+    }
+    return $result;
+  }
+
+  /**
+   * Adds the data of the given wrapper to the given XML element.
+   */
+  public static function addToXML(DOMDocument $doc, DOMNode $parent, $wrapper) {
+    $filtered = restws_property_access_filter($wrapper);
+    foreach ($filtered as $name => $property) {
+      try {
+        if ($property instanceof EntityDrupalWrapper) {
+          // For referenced entities only return the URI.
+          if ($id = $property->getIdentifier()) {
+            $element = $doc->createElement(is_numeric($name) ? 'item' : $name);
+            $parent->appendChild($element);
+            self::setXMLReference($element, $property->type(), $id);
+          }
+        }
+        elseif ($property instanceof EntityValueWrapper) {
+          // Only primitive data types are allowed here. There might be complex
+          // arrays/objects in EntityValueWrapper if no property information is
+          // provided (example: the "data" property of commerce_price fields.
+          if (is_scalar($property->value())) {
+            $escaped = $doc->createTextNode($property->value());
+            $element = $doc->createElement(is_numeric($name) ? 'item' : $name);
+            $element->appendChild($escaped);
+            $parent->appendChild($element);
+          }
+        }
+        elseif ($property instanceof EntityListWrapper || $property instanceof EntityStructureWrapper) {
+          $element = $doc->createElement(is_numeric($name) ? 'item' : $name);
+          $parent->appendChild($element);
+          self::addToXML($doc, $element, $property);
+        }
+      }
+      catch (EntityMetadataWrapperException $e) {
+        // A property causes problems - ignore that.
+      }
+    }
+  }
+
+  public static function setXMLReference(DOMElement $node, $resource, $id) {
+    $node->nodeValue = restws_resource_uri($resource, $id);
+    $node->setAttribute('resource', $resource);
+    $node->setAttribute('id', $id);
+  }
+}
+
+/**
+ * A simple formatter for RDF. Requires the RDF module for the mapping.
+ */
+class RestWSFormatRDF extends RestWSBaseFormat {
+
+  protected $namespaces;
+
+  public function __construct($name, $info) {
+    parent::__construct($name, $info);
+    $this->namespaces = rdf_get_namespaces();
+    $this->namespaces['rdf'] = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#';
+  }
+
+  /**
+   * Gets the representation of a resource.
+   */
+  public function viewResource($resourceController, $id) {
+    $xml = new DOMDocument('1.0', 'utf-8');
+    $rdf_element = $xml->createElementNS($this->namespaces['rdf'], 'rdf:RDF');
+    $xml->appendChild($rdf_element);
+
+    $element = $xml->createElementNS($this->namespaces['rdf'], 'rdf:Description');
+    $element->setAttributeNS($this->namespaces['rdf'], 'rdf:about', restws_resource_uri($resourceController->resource(), $id));
+
+    // Add the RDF type of the resource if there is a mapping.
+    $entity = $resourceController->read($id);
+    if (!empty($entity->rdf_mapping['rdftype'])) {
+      foreach ($entity->rdf_mapping['rdftype'] as $rdf_type) {
+        $type_element = $xml->createElementNS($this->namespaces['rdf'], 'rdf:type');
+        list($ns, $name) = explode(':', $rdf_type);
+        $type_element->setAttributeNS($this->namespaces['rdf'], 'rdf:resource', $this->namespaces[$ns] . $name);
+        $element->appendChild($type_element);
+      }
+    }
+
+    $this->addToXML($xml, $element, $resourceController->wrapper($id));
+    $rdf_element->appendChild($element);
+
+    $function = __FUNCTION__;
+    drupal_alter('restws_response', $xml, $function, $this->formatName);
+
+    return $xml->saveXML();
+  }
+
+  public function createResource($resourceController, $data) {
+    throw new RestWSException('Not implemented', 501);
+  }
+
+  public function updateResource($resourceController, $id, $data) {
+    throw new RestWSException('Not implemented', 501);
+  }
+
+  public function queryResource($resourceController, $parameters) {
+    throw new RestWSException('Not implemented', 501);
+  }
+
+  /**
+   * Adds the data of the given wrapper to the given XML element.
+   */
+  public function addToXML(DOMDocument $doc, DOMNode $parent, $wrapper) {
+    $filtered = restws_property_access_filter($wrapper);
+    foreach ($filtered as $name => $property) {
+      try {
+        if ($property instanceof EntityDrupalWrapper) {
+          // For referenced entities only return the URI.
+          if ($id = $property->getIdentifier()) {
+            $element = $this->addRdfElement($doc, $wrapper, $name);
+            $parent->appendChild($element);
+            $this->addReference($doc, $element, $property->type(), $id);
+          }
+        }
+        elseif ($property instanceof EntityValueWrapper) {
+          $element = $this->addRdfElement($doc, $wrapper, $name);
+          $parent->appendChild($element);
+          $element->nodeValue = $property->value();
+        }
+        elseif ($property instanceof EntityListWrapper || $property instanceof EntityStructureWrapper) {
+          $element = $this->addRdfElement($doc, $wrapper, $name);
+          $parent->appendChild($element);
+          $node = $doc->createElementNS($this->namespaces['rdf'], 'rdf:Description');
+          $element->appendChild($node);
+          $this->addToXML($doc, $node, $property);
+        }
+      }
+      catch (EntityMetadataWrapperException $e) {
+        // A property causes problems - ignore that.
+      }
+    }
+  }
+
+  public function addReference(DomDocument $doc, DOMElement $node, $resource, $id) {
+    $element = $doc->createElementNS($this->namespaces['rdf'], 'rdf:Description');
+    $element->setAttributeNS($this->namespaces['rdf'], 'rdf:about', restws_resource_uri($resource, $id));
+    $node->appendChild($element);
+  }
+
+  /**
+   * Adds an RDF element for the given property of the wrapper using the RDF
+   * mapping.
+   */
+  public function addRdfElement(DOMDOcument $doc, EntityMetadataWrapper $wrapper, $name) {
+    if ($wrapper instanceof EntityDrupalWrapper) {
+      $entity = $wrapper->value();
+      if (!empty($entity->rdf_mapping[$name])) {
+        // Just make use of the first predicate for now.
+        $predicate = reset($entity->rdf_mapping[$name]['predicates']);
+        list($ns, $qname) = explode(':', $predicate);
+        $element = $doc->createElementNS($this->namespaces[$ns], $predicate);
+
+        if (!empty($entity->rdf_mapping[$name]['datatype'])) {
+          $element->setAttributeNS($this->namespaces['rdf'], 'rdf:datatype', $entity->rdf_mapping[$name]['datatype']);
+        }
+      }
+    }
+    if (!isset($element)) {
+      // For other elements just use the site URL as namespace.
+      $element = $doc->createElementNS(url('', array('absolute' => TRUE)), 'site:' . (is_numeric($name) ? 'item' : $name));
+    }
+    return $element;
+  }
+}