entity.inc

<?php


/**
 * Interface for entity controller classes.
 *
 * All entity controller classes specified via the 'controller class' key
 * returned by hook_entity_info() or hook_entity_info_alter() have to implement
 * this interface.
 *
 * Most simple, SQL-based entity controllers will do better by extending
 * DrupalDefaultEntityController instead of implementing this interface
 * directly.
 */
interface DrupalEntityControllerInterface {
    
    /**
     * Resets the internal, static entity cache.
     *
     * @param $ids
     *   (optional) If specified, the cache is reset for the entities with the
     *   given ids only.
     */
    public function resetCache(array $ids = NULL);
    
    /**
     * Loads one or more entities.
     *
     * @param $ids
     *   An array of entity IDs, or FALSE to load all entities.
     * @param $conditions
     *   An array of conditions. Keys are field names on the entity's base table.
     *   Values will be compared for equality. All the comparisons will be ANDed
     *   together. This parameter is deprecated; use an EntityFieldQuery instead.
     *
     * @return
     *   An array of entity objects indexed by their ids. When no results are
     *   found, an empty array is returned.
     */
    public function load($ids = array(), $conditions = array());

}

/**
 * Default implementation of DrupalEntityControllerInterface.
 *
 * This class can be used as-is by most simple entity types. Entity types
 * requiring special handling can extend the class.
 */
class DrupalDefaultEntityController implements DrupalEntityControllerInterface {
    
    /**
     * Static cache of entities, keyed by entity ID.
     *
     * @var array
     */
    protected $entityCache;
    
    /**
     * Entity type for this controller instance.
     *
     * @var string
     */
    protected $entityType;
    
    /**
     * Array of information about the entity.
     *
     * @var array
     *
     * @see entity_get_info()
     */
    protected $entityInfo;
    
    /**
     * Additional arguments to pass to hook_TYPE_load().
     *
     * Set before calling DrupalDefaultEntityController::attachLoad().
     *
     * @var array
     */
    protected $hookLoadArguments;
    
    /**
     * Name of the entity's ID field in the entity database table.
     *
     * @var string
     */
    protected $idKey;
    
    /**
     * Name of entity's revision database table field, if it supports revisions.
     *
     * Has the value FALSE if this entity does not use revisions.
     *
     * @var string
     */
    protected $revisionKey;
    
    /**
     * The table that stores revisions, if the entity supports revisions.
     *
     * @var string
     */
    protected $revisionTable;
    
    /**
     * Whether this entity type should use the static cache.
     *
     * Set by entity info.
     *
     * @var boolean
     */
    protected $cache;
    
    /**
     * Constructor: sets basic variables.
     *
     * @param $entityType
     *   The entity type for which the instance is created.
     */
    public function __construct($entityType) {
        $this->entityType = $entityType;
        $this->entityInfo = entity_get_info($entityType);
        $this->entityCache = array();
        $this->hookLoadArguments = array();
        $this->idKey = $this->entityInfo['entity keys']['id'];
        // Check if the entity type supports revisions.
        if (!empty($this->entityInfo['entity keys']['revision'])) {
            $this->revisionKey = $this->entityInfo['entity keys']['revision'];
            $this->revisionTable = $this->entityInfo['revision table'];
        }
        else {
            $this->revisionKey = FALSE;
        }
        // Check if the entity type supports static caching of loaded entities.
        $this->cache = !empty($this->entityInfo['static cache']);
    }
    
    /**
     * Implements DrupalEntityControllerInterface::resetCache().
     */
    public function resetCache(array $ids = NULL) {
        if (isset($ids)) {
            foreach ($ids as $id) {
                unset($this->entityCache[$id]);
            }
        }
        else {
            $this->entityCache = array();
        }
    }
    
    /**
     * Implements DrupalEntityControllerInterface::load().
     */
    public function load($ids = array(), $conditions = array()) {
        $entities = array();
        // Revisions are not statically cached, and require a different query to
        // other conditions, so separate the revision id into its own variable.
        if ($this->revisionKey && isset($conditions[$this->revisionKey])) {
            $revision_id = $conditions[$this->revisionKey];
            unset($conditions[$this->revisionKey]);
        }
        else {
            $revision_id = FALSE;
        }
        // Create a new variable which is either a prepared version of the $ids
        // array for later comparison with the entity cache, or FALSE if no $ids
        // were passed. The $ids array is reduced as items are loaded from cache,
        // and we need to know if it's empty for this reason to avoid querying the
        // database when all requested entities are loaded from cache.
        $passed_ids = !empty($ids) ? array_flip($ids) : FALSE;
        // Try to load entities from the static cache, if the entity type supports
        // static caching.
        if ($this->cache && !$revision_id) {
            $entities += $this->cacheGet($ids, $conditions);
            // If any entities were loaded, remove them from the ids still to load.
            if ($passed_ids) {
                $ids = array_keys(array_diff_key($passed_ids, $entities));
            }
        }
        // Ensure integer entity IDs are valid.
        if (!empty($ids)) {
            $this->cleanIds($ids);
        }
        // Load any remaining entities from the database. This is the case if $ids
        // is set to FALSE (so we load all entities), if there are any ids left to
        // load, if loading a revision, or if $conditions was passed without $ids.
        if ($ids === FALSE || $ids || $revision_id || $conditions && !$passed_ids) {
            // Build the query.
            $query = $this->buildQuery($ids, $conditions, $revision_id);
            $queried_entities = $query->execute()
                ->fetchAllAssoc($this->idKey);
        }
        // Pass all entities loaded from the database through $this->attachLoad(),
        // which attaches fields (if supported by the entity type) and calls the
        // entity type specific load callback, for example hook_node_load().
        if (!empty($queried_entities)) {
            $this->attachLoad($queried_entities, $revision_id);
            $entities += $queried_entities;
        }
        if ($this->cache) {
            // Add entities to the cache if we are not loading a revision.
            if (!empty($queried_entities) && !$revision_id) {
                $this->cacheSet($queried_entities);
            }
        }
        // Ensure that the returned array is ordered the same as the original
        // $ids array if this was passed in and remove any invalid ids.
        if ($passed_ids) {
            // Remove any invalid ids from the array.
            $passed_ids = array_intersect_key($passed_ids, $entities);
            foreach ($entities as $entity) {
                $passed_ids[$entity->{$this->idKey}] = $entity;
            }
            $entities = $passed_ids;
        }
        return $entities;
    }
    
    /**
     * Ensures integer entity IDs are valid.
     *
     * The identifier sanitization provided by this method has been introduced
     * as Drupal used to rely on the database to facilitate this, which worked
     * correctly with MySQL but led to errors with other DBMS such as PostgreSQL.
     *
     * @param array $ids
     *   The entity IDs to verify. Non-integer IDs are removed from this array if
     *   the entity type requires IDs to be integers.
     */
    protected function cleanIds(&$ids) {
        $entity_info = entity_get_info($this->entityType);
        if (isset($entity_info['base table field types'])) {
            $id_type = $entity_info['base table field types'][$this->idKey];
            if ($id_type == 'serial' || $id_type == 'int') {
                $ids = array_filter($ids, array(
                    $this,
                    'filterId',
                ));
                $ids = array_map('intval', $ids);
            }
        }
    }
    
    /**
     * Callback for array_filter that removes non-integer IDs.
     */
    protected function filterId($id) {
        // ctype_digit() is used here instead of a strict comparison as sometimes
        // the id is passed as a string containing '0' which may represent a bug
        // elsewhere but would fail with a strict comparison.
        return is_numeric($id) && $id == (int) $id && ctype_digit((string) $id);
    }
    
    /**
     * Builds the query to load the entity.
     *
     * This has full revision support. For entities requiring special queries,
     * the class can be extended, and the default query can be constructed by
     * calling parent::buildQuery(). This is usually necessary when the object
     * being loaded needs to be augmented with additional data from another
     * table, such as loading node type into comments or vocabulary machine name
     * into terms, however it can also support $conditions on different tables.
     * See CommentController::buildQuery() or TaxonomyTermController::buildQuery()
     * for examples.
     *
     * @param $ids
     *   An array of entity IDs, or FALSE to load all entities.
     * @param $conditions
     *   An array of conditions. Keys are field names on the entity's base table.
     *   Values will be compared for equality. All the comparisons will be ANDed
     *   together. This parameter is deprecated; use an EntityFieldQuery instead.
     * @param $revision_id
     *   The ID of the revision to load, or FALSE if this query is asking for the
     *   most current revision(s).
     *
     * @return SelectQuery
     *   A SelectQuery object for loading the entity.
     */
    protected function buildQuery($ids, $conditions = array(), $revision_id = FALSE) {
        $query = db_select($this->entityInfo['base table'], 'base');
        $query->addTag($this->entityType . '_load_multiple');
        if ($revision_id) {
            $query->join($this->revisionTable, 'revision', "revision.{$this->idKey} = base.{$this->idKey} AND revision.{$this->revisionKey} = :revisionId", array(
                ':revisionId' => $revision_id,
            ));
        }
        elseif ($this->revisionKey) {
            $query->join($this->revisionTable, 'revision', "revision.{$this->revisionKey} = base.{$this->revisionKey}");
        }
        // Add fields from the {entity} table.
        $entity_fields = $this->entityInfo['schema_fields_sql']['base table'];
        if ($this->revisionKey) {
            // Add all fields from the {entity_revision} table.
            $entity_revision_fields = drupal_map_assoc($this->entityInfo['schema_fields_sql']['revision table']);
            // The id field is provided by entity, so remove it.
            unset($entity_revision_fields[$this->idKey]);
            // Remove all fields from the base table that are also fields by the same
            // name in the revision table.
            $entity_field_keys = array_flip($entity_fields);
            foreach ($entity_revision_fields as $key => $name) {
                if (isset($entity_field_keys[$name])) {
                    unset($entity_fields[$entity_field_keys[$name]]);
                }
            }
            $query->fields('revision', $entity_revision_fields);
        }
        $query->fields('base', $entity_fields);
        if ($ids) {
            $query->condition("base.{$this->idKey}", $ids, 'IN');
        }
        if ($conditions) {
            foreach ($conditions as $field => $value) {
                $query->condition('base.' . $field, $value);
            }
        }
        return $query;
    }
    
    /**
     * Attaches data to entities upon loading.
     *
     * This will attach fields, if the entity is fieldable. It calls
     * hook_entity_load() for modules which need to add data to all entities.
     * It also calls hook_TYPE_load() on the loaded entities. For example
     * hook_node_load() or hook_user_load(). If your hook_TYPE_load()
     * expects special parameters apart from the queried entities, you can set
     * $this->hookLoadArguments prior to calling the method.
     * See NodeController::attachLoad() for an example.
     *
     * @param $queried_entities
     *   Associative array of query results, keyed on the entity ID.
     * @param $revision_id
     *   ID of the revision that was loaded, or FALSE if the most current revision
     *   was loaded.
     */
    protected function attachLoad(&$queried_entities, $revision_id = FALSE) {
        // Attach fields.
        if ($this->entityInfo['fieldable']) {
            if ($revision_id) {
                field_attach_load_revision($this->entityType, $queried_entities);
            }
            else {
                field_attach_load($this->entityType, $queried_entities);
            }
        }
        // Call hook_entity_load().
        foreach (module_implements('entity_load') as $module) {
            $function = $module . '_entity_load';
            $function($queried_entities, $this->entityType);
        }
        // Call hook_TYPE_load(). The first argument for hook_TYPE_load() are
        // always the queried entities, followed by additional arguments set in
        // $this->hookLoadArguments.
        $args = array_merge(array(
            $queried_entities,
        ), $this->hookLoadArguments);
        foreach (module_implements($this->entityInfo['load hook']) as $module) {
            call_user_func_array($module . '_' . $this->entityInfo['load hook'], $args);
        }
    }
    
    /**
     * Gets entities from the static cache.
     *
     * @param $ids
     *   If not empty, return entities that match these IDs.
     * @param $conditions
     *   If set, return entities that match all of these conditions.
     *
     * @return
     *   Array of entities from the entity cache.
     */
    protected function cacheGet($ids, $conditions = array()) {
        $entities = array();
        // Load any available entities from the internal cache.
        if (!empty($this->entityCache)) {
            if ($ids) {
                $entities += array_intersect_key($this->entityCache, array_flip($ids));
            }
            elseif ($conditions) {
                $entities = $this->entityCache;
            }
        }
        // Exclude any entities loaded from cache if they don't match $conditions.
        // This ensures the same behavior whether loading from memory or database.
        if ($conditions) {
            foreach ($entities as $entity) {
                // Iterate over all conditions and compare them to the entity
                // properties. We cannot use array_diff_assoc() here since the
                // conditions can be nested arrays, too.
                foreach ($conditions as $property_name => $condition) {
                    if (is_array($condition)) {
                        // Multiple condition values for one property are treated as OR
                        // operation: only if the value is not at all in the condition array
                        // we remove the entity.
                        if (!in_array($entity->{$property_name}, $condition)) {
                            unset($entities[$entity->{$this->idKey}]);
                            continue 2;
                        }
                    }
                    elseif ($condition != $entity->{$property_name}) {
                        unset($entities[$entity->{$this->idKey}]);
                        continue 2;
                    }
                }
            }
        }
        return $entities;
    }
    
    /**
     * Stores entities in the static entity cache.
     *
     * @param $entities
     *   Entities to store in the cache.
     */
    protected function cacheSet($entities) {
        $this->entityCache += $entities;
    }

}

/**
 * Exception thrown by EntityFieldQuery() on unsupported query syntax.
 *
 * Some storage modules might not support the full range of the syntax for
 * conditions, and will raise an EntityFieldQueryException when an unsupported
 * condition was specified.
 */
class EntityFieldQueryException extends Exception {

}

/**
 * Retrieves entities matching a given set of conditions.
 *
 * This class allows finding entities based on entity properties (for example,
 * node->changed), field values, and generic entity meta data (bundle,
 * entity type, entity ID, and revision ID). It is not possible to query across
 * multiple entity types. For example, there is no facility to find published
 * nodes written by users created in the last hour, as this would require
 * querying both node->status and user->created.
 *
 * Normally we would not want to have public properties on the object, as that
 * allows the object's state to become inconsistent too easily. However, this
 * class's standard use case involves primarily code that does need to have
 * direct access to the collected properties in order to handle alternate
 * execution routines. We therefore use public properties for simplicity. Note
 * that code that is simply creating and running a field query should still use
 * the appropriate methods to add conditions on the query.
 *
 * Storage engines are not required to support every type of query. By default,
 * an EntityFieldQueryException will be raised if an unsupported condition is
 * specified or if the query has field conditions or sorts that are stored in
 * different field storage engines. However, this logic can be overridden in
 * hook_entity_query_alter().
 *
 * Also note that this query does not automatically respect entity access
 * restrictions. Node access control is performed by the SQL storage engine but
 * other storage engines might not do this.
 */
class EntityFieldQuery {
    
    /**
     * Indicates that both deleted and non-deleted fields should be returned.
     *
     * @see EntityFieldQuery::deleted()
     */
    const RETURN_ALL = NULL;
    
    /**
     * TRUE if the query has already been altered, FALSE if it hasn't.
     *
     * Used in alter hooks to check for cloned queries that have already been
     * altered prior to the clone (for example, the pager count query).
     *
     * @var boolean
     */
    public $altered = FALSE;
    
    /**
     * Associative array of entity-generic metadata conditions.
     *
     * @var array
     *
     * @see EntityFieldQuery::entityCondition()
     */
    public $entityConditions = array();
    
    /**
     * List of field conditions.
     *
     * @var array
     *
     * @see EntityFieldQuery::fieldCondition()
     */
    public $fieldConditions = array();
    
    /**
     * List of field meta conditions (language and delta).
     *
     * Field conditions operate on columns specified by hook_field_schema(),
     * the meta conditions operate on columns added by the system: delta
     * and language. These can not be mixed with the field conditions because
     * field columns can have any name including delta and language.
     *
     * @var array
     *
     * @see EntityFieldQuery::fieldLanguageCondition()
     * @see EntityFieldQuery::fieldDeltaCondition()
     */
    public $fieldMetaConditions = array();
    
    /**
     * List of property conditions.
     *
     * @var array
     *
     * @see EntityFieldQuery::propertyCondition()
     */
    public $propertyConditions = array();
    
    /**
     * List of order clauses.
     *
     * @var array
     */
    public $order = array();
    
    /**
     * The query range.
     *
     * @var array
     *
     * @see EntityFieldQuery::range()
     */
    public $range = array();
    
    /**
     * The query pager data.
     *
     * @var array
     *
     * @see EntityFieldQuery::pager()
     */
    public $pager = array();
    
    /**
     * Query behavior for deleted data.
     *
     * TRUE to return only deleted data, FALSE to return only non-deleted data,
     * EntityFieldQuery::RETURN_ALL to return everything.
     *
     * @see EntityFieldQuery::deleted()
     */
    public $deleted = FALSE;
    
    /**
     * A list of field arrays used.
     *
     * Field names passed to EntityFieldQuery::fieldCondition() and
     * EntityFieldQuery::fieldOrderBy() are run through field_info_field() before
     * stored in this array. This way, the elements of this array are field
     * arrays.
     *
     * @var array
     */
    public $fields = array();
    
    /**
     * TRUE if this is a count query, FALSE if it isn't.
     *
     * @var boolean
     */
    public $count = FALSE;
    
    /**
     * Flag indicating whether this is querying current or all revisions.
     *
     * @var int
     *
     * @see EntityFieldQuery::age()
     */
    public $age = FIELD_LOAD_CURRENT;
    
    /**
     * A list of the tags added to this query.
     *
     * @var array
     *
     * @see EntityFieldQuery::addTag()
     */
    public $tags = array();
    
    /**
     * A list of metadata added to this query.
     *
     * @var array
     *
     * @see EntityFieldQuery::addMetaData()
     */
    public $metaData = array();
    
    /**
     * The ordered results.
     *
     * @var array
     *
     * @see EntityFieldQuery::execute().
     */
    public $ordered_results = array();
    
    /**
     * The method executing the query, if it is overriding the default.
     *
     * @var string
     *
     * @see EntityFieldQuery::execute().
     */
    public $executeCallback = '';
    
    /**
     * Adds a condition on entity-generic metadata.
     *
     * If the overall query contains only entity conditions or ordering, or if
     * there are property conditions, then specifying the entity type is
     * mandatory. If there are field conditions or ordering but no property
     * conditions or ordering, then specifying an entity type is optional. While
     * the field storage engine might support field conditions on more than one
     * entity type, there is no way to query across multiple entity base tables by
     * default. To specify the entity type, pass in 'entity_type' for $name,
     * the type as a string for $value, and no $operator (it's disregarded).
     *
     * 'bundle', 'revision_id' and 'entity_id' have no such restrictions.
     *
     * Note: The "comment" entity type does not support bundle conditions.
     *
     * @param $name
     *   'entity_type', 'bundle', 'revision_id' or 'entity_id'.
     * @param $value
     *   The value for $name. In most cases, this is a scalar. For more complex
     *   options, it is an array. The meaning of each element in the array is
     *   dependent on $operator.
     * @param $operator
     *   Possible values:
     *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
     *     operators expect $value to be a literal of the same type as the
     *     column.
     *   - 'IN', 'NOT IN': These operators expect $value to be an array of
     *     literals of the same type as the column.
     *   - 'BETWEEN': This operator expects $value to be an array of two literals
     *     of the same type as the column.
     *   The operator can be omitted, and will default to 'IN' if the value is an
     *   array, or to '=' otherwise.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function entityCondition($name, $value, $operator = NULL) {
        // The '!=' operator is deprecated in favour of the '<>' operator since the
        // latter is ANSI SQL compatible.
        if ($operator == '!=') {
            $operator = '<>';
        }
        $this->entityConditions[$name] = array(
            'value' => $value,
            'operator' => $operator,
        );
        return $this;
    }
    
    /**
     * Adds a condition on field values.
     *
     * Note that entities with empty field values will be excluded from the
     * EntityFieldQuery results when using this method.
     *
     * @param $field
     *   Either a field name or a field array.
     * @param $column
     *   The column that should hold the value to be matched, defined in the
     *   hook_field_schema() of this field. If this is omitted then all of the
     *   other parameters are ignored, except $field, and this call will just be
     *   adding a condition that says that the field has a value, rather than
     *   testing the value itself.
     * @param $value
     *   The value to test the column value against. In most cases, this is a
     *   scalar. For more complex options, it is an array. The meaning of each
     *   element in the array is dependent on $operator.
     * @param $operator
     *   The operator to be used to test the given value. The possible values are:
     *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
     *     operators expect $value to be a literal of the same type as the
     *     column.
     *   - 'IN', 'NOT IN': These operators expect $value to be an array of
     *     literals of the same type as the column.
     *   - 'BETWEEN': This operator expects $value to be an array of two literals
     *     of the same type as the column.
     *   The operator can be omitted, and will default to 'IN' if the value is an
     *   array, or to '=' otherwise.
     * @param $delta_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $delta_group. For example, let's presume a multivalue field which has
     *   two columns, 'color' and 'shape', and for entity ID 1, there are two
     *   values: red/square and blue/circle. Entity ID 1 does not have values
     *   corresponding to 'red circle'; however if you pass 'red' and 'circle' as
     *   conditions, it will appear in the results -- by default queries will run
     *   against any combination of deltas. By passing the conditions with the
     *   same $delta_group it will ensure that only values attached to the same
     *   delta are matched, and entity 1 would then be excluded from the results.
     * @param $language_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $language_group.
     *
     * @return EntityFieldQuery
     *   The called object.
     *
     * @see EntityFieldQuery::addFieldCondition
     * @see EntityFieldQuery::deleted
     */
    public function fieldCondition($field, $column = NULL, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
        return $this->addFieldCondition($this->fieldConditions, $field, $column, $value, $operator, $delta_group, $language_group);
    }
    
    /**
     * Adds a condition on the field language column.
     *
     * @param $field
     *   Either a field name or a field array.
     * @param $value
     *   The value to test the column value against.
     * @param $operator
     *   The operator to be used to test the given value.
     * @param $delta_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $delta_group.
     * @param $language_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $language_group.
     *
     * @return EntityFieldQuery
     *   The called object.
     *
     * @see EntityFieldQuery::addFieldCondition
     * @see EntityFieldQuery::deleted
     */
    public function fieldLanguageCondition($field, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
        return $this->addFieldCondition($this->fieldMetaConditions, $field, 'language', $value, $operator, $delta_group, $language_group);
    }
    
    /**
     * Adds a condition on the field delta column.
     *
     * @param $field
     *   Either a field name or a field array.
     * @param $value
     *   The value to test the column value against.
     * @param $operator
     *   The operator to be used to test the given value.
     * @param $delta_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $delta_group.
     * @param $language_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $language_group.
     *
     * @return EntityFieldQuery
     *   The called object.
     *
     * @see EntityFieldQuery::addFieldCondition
     * @see EntityFieldQuery::deleted
     */
    public function fieldDeltaCondition($field, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
        return $this->addFieldCondition($this->fieldMetaConditions, $field, 'delta', $value, $operator, $delta_group, $language_group);
    }
    
    /**
     * Adds the given condition to the proper condition array.
     *
     * @param $conditions
     *   A reference to an array of conditions.
     * @param $field
     *   Either a field name or a field array.
     * @param $column
     *   The column that should hold the value to be matched, defined in the
     *   hook_field_schema() of this field. If this is omitted then all of the
     *   other parameters are ignored, except $field, and this call will just be
     *   adding a condition that says that the field has a value, rather than
     *   testing the value itself.
     * @param $value
     *   The value to test the column value against. In most cases, this is a
     *   scalar. For more complex options, it is an array. The meaning of each
     *   element in the array is dependent on $operator.
     * @param $operator
     *   Possible values:
     *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
     *     operators expect $value to be a literal of the same type as the
     *     column.
     *   - 'IN', 'NOT IN': These operators expect $value to be an array of
     *     literals of the same type as the column.
     *   - 'BETWEEN': This operator expects $value to be an array of two literals
     *     of the same type as the column.
     *   The operator can be omitted, and will default to 'IN' if the value is an
     *   array, or to '=' otherwise.
     * @param $delta_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $delta_group. For example, let's presume a multivalue field which has
     *   two columns, 'color' and 'shape', and for entity ID 1, there are two
     *   values: red/square and blue/circle. Entity ID 1 does not have values
     *   corresponding to 'red circle', however if you pass 'red' and 'circle' as
     *   conditions, it will appear in the results -- by default queries will run
     *   against any combination of deltas. By passing the conditions with the
     *   same $delta_group it will ensure that only values attached to the same
     *   delta are matched, and entity 1 would then be excluded from the results.
     * @param $language_group
     *   An arbitrary identifier: conditions in the same group must have the same
     *   $language_group.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    protected function addFieldCondition(&$conditions, $field, $column = NULL, $value = NULL, $operator = NULL, $delta_group = NULL, $language_group = NULL) {
        // The '!=' operator is deprecated in favour of the '<>' operator since the
        // latter is ANSI SQL compatible.
        if ($operator == '!=') {
            $operator = '<>';
        }
        if (is_scalar($field)) {
            $field_definition = field_info_field($field);
            if (empty($field_definition)) {
                throw new EntityFieldQueryException(t('Unknown field: @field_name', array(
                    '@field_name' => $field,
                )));
            }
            $field = $field_definition;
        }
        // Ensure the same index is used for field conditions as for fields.
        $index = count($this->fields);
        $this->fields[$index] = $field;
        if (isset($column)) {
            $conditions[$index] = array(
                'field' => $field,
                'column' => $column,
                'value' => $value,
                'operator' => $operator,
                'delta_group' => $delta_group,
                'language_group' => $language_group,
            );
        }
        return $this;
    }
    
    /**
     * Adds a condition on an entity-specific property.
     *
     * An $entity_type must be specified by calling
     * EntityFieldCondition::entityCondition('entity_type', $entity_type) before
     * executing the query. Also, by default only entities stored in SQL are
     * supported; however, EntityFieldQuery::executeCallback can be set to handle
     * different entity storage.
     *
     * @param $column
     *   A column defined in the hook_schema() of the base table of the entity.
     * @param $value
     *   The value to test the field against. In most cases, this is a scalar. For
     *   more complex options, it is an array. The meaning of each element in the
     *   array is dependent on $operator.
     * @param $operator
     *   Possible values:
     *   - '=', '<>', '>', '>=', '<', '<=', 'STARTS_WITH', 'CONTAINS': These
     *     operators expect $value to be a literal of the same type as the
     *     column.
     *   - 'IN', 'NOT IN': These operators expect $value to be an array of
     *     literals of the same type as the column.
     *   - 'BETWEEN': This operator expects $value to be an array of two literals
     *     of the same type as the column.
     *   The operator can be omitted, and will default to 'IN' if the value is an
     *   array, or to '=' otherwise.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function propertyCondition($column, $value, $operator = NULL) {
        // The '!=' operator is deprecated in favour of the '<>' operator since the
        // latter is ANSI SQL compatible.
        if ($operator == '!=') {
            $operator = '<>';
        }
        $this->propertyConditions[] = array(
            'column' => $column,
            'value' => $value,
            'operator' => $operator,
        );
        return $this;
    }
    
    /**
     * Orders the result set by entity-generic metadata.
     *
     * If called multiple times, the query will order by each specified column in
     * the order this method is called.
     *
     * Note: The "comment" and "taxonomy_term" entity types don't support ordering
     * by bundle. For "taxonomy_term", propertyOrderBy('vid') can be used instead.
     *
     * @param $name
     *   'entity_type', 'bundle', 'revision_id' or 'entity_id'.
     * @param $direction
     *   The direction to sort. Legal values are "ASC" and "DESC".
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function entityOrderBy($name, $direction = 'ASC') {
        $this->order[] = array(
            'type' => 'entity',
            'specifier' => $name,
            'direction' => $direction,
        );
        return $this;
    }
    
    /**
     * Orders the result set by a given field column.
     *
     * If called multiple times, the query will order by each specified column in
     * the order this method is called. Note that entities with empty field
     * values will be excluded from the EntityFieldQuery results when using this
     * method.
     *
     * @param $field
     *   Either a field name or a field array.
     * @param $column
     *   A column defined in the hook_field_schema() of this field. entity_id and
     *   bundle can also be used.
     * @param $direction
     *   The direction to sort. Legal values are "ASC" and "DESC".
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function fieldOrderBy($field, $column, $direction = 'ASC') {
        if (is_scalar($field)) {
            $field_definition = field_info_field($field);
            if (empty($field_definition)) {
                throw new EntityFieldQueryException(t('Unknown field: @field_name', array(
                    '@field_name' => $field,
                )));
            }
            $field = $field_definition;
        }
        // Save the index used for the new field, for later use in field storage.
        $index = count($this->fields);
        $this->fields[$index] = $field;
        $this->order[] = array(
            'type' => 'field',
            'specifier' => array(
                'field' => $field,
                'index' => $index,
                'column' => $column,
            ),
            'direction' => $direction,
        );
        return $this;
    }
    
    /**
     * Orders the result set by an entity-specific property.
     *
     * An $entity_type must be specified by calling
     * EntityFieldCondition::entityCondition('entity_type', $entity_type) before
     * executing the query.
     *
     * If called multiple times, the query will order by each specified column in
     * the order this method is called.
     *
     * @param $column
     *   The column on which to order.
     * @param $direction
     *   The direction to sort. Legal values are "ASC" and "DESC".
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function propertyOrderBy($column, $direction = 'ASC') {
        $this->order[] = array(
            'type' => 'property',
            'specifier' => $column,
            'direction' => $direction,
        );
        return $this;
    }
    
    /**
     * Sets the query to be a count query only.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function count() {
        $this->count = TRUE;
        return $this;
    }
    
    /**
     * Restricts a query to a given range in the result set.
     *
     * @param $start
     *   The first entity from the result set to return. If NULL, removes any
     *   range directives that are set.
     * @param $length
     *   The number of entities to return from the result set.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function range($start = NULL, $length = NULL) {
        $this->range = array(
            'start' => $start,
            'length' => $length,
        );
        return $this;
    }
    
    /**
     * Enables a pager for the query.
     *
     * @param $limit
     *   An integer specifying the number of elements per page.  If passed a false
     *   value (FALSE, 0, NULL), the pager is disabled.
     * @param $element
     *   An optional integer to distinguish between multiple pagers on one page.
     *   If not provided, one is automatically calculated.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function pager($limit = 10, $element = NULL) {
        if (!isset($element)) {
            $element = PagerDefault::$maxElement++;
        }
        elseif ($element >= PagerDefault::$maxElement) {
            PagerDefault::$maxElement = $element + 1;
        }
        $this->pager = array(
            'limit' => $limit,
            'element' => $element,
        );
        return $this;
    }
    
    /**
     * Enables sortable tables for this query.
     *
     * @param $headers
     *   An EFQ Header array based on which the order clause is added to the
     *   query.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function tableSort(&$headers) {
        // If 'field' is not initialized, the header columns aren't clickable
        foreach ($headers as $key => $header) {
            if (is_array($header) && isset($header['specifier'])) {
                $headers[$key]['field'] = '';
            }
        }
        $order = tablesort_get_order($headers);
        $direction = tablesort_get_sort($headers);
        foreach ($headers as $header) {
            if (is_array($header) && $header['data'] == $order['name']) {
                if ($header['type'] == 'field') {
                    $this->fieldOrderBy($header['specifier']['field'], $header['specifier']['column'], $direction);
                }
                else {
                    $header['direction'] = $direction;
                    $this->order[] = $header;
                }
            }
        }
        return $this;
    }
    
    /**
     * Filters on the data being deleted.
     *
     * @param $deleted
     *   TRUE to only return deleted data, FALSE to return non-deleted data,
     *   EntityFieldQuery::RETURN_ALL to return everything. Defaults to FALSE.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function deleted($deleted = TRUE) {
        $this->deleted = $deleted;
        return $this;
    }
    
    /**
     * Queries the current or every revision.
     *
     * Note that this only affects field conditions. Property conditions always
     * apply to the current revision.
     * @TODO: Once revision tables have been cleaned up, revisit this.
     *
     * @param $age
     *   - FIELD_LOAD_CURRENT (default): Query the most recent revisions for all
     *     entities. The results will be keyed by entity type and entity ID.
     *   - FIELD_LOAD_REVISION: Query all revisions. The results will be keyed by
     *     entity type and entity revision ID.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function age($age) {
        $this->age = $age;
        return $this;
    }
    
    /**
     * Adds a tag to the query.
     *
     * Tags are strings that mark a query so that hook_query_alter() and
     * hook_query_TAG_alter() implementations may decide if they wish to alter
     * the query. A query may have any number of tags, and they must be valid PHP
     * identifiers (composed of letters, numbers, and underscores). For example,
     * queries involving nodes that will be displayed for a user need to add the
     * tag 'node_access', so that the node module can add access restrictions to
     * the query.
     *
     * If an entity field query has tags, it must also have an entity type
     * specified, because the alter hook will need the entity base table.
     *
     * @param string $tag
     *   The tag to add.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function addTag($tag) {
        $this->tags[$tag] = $tag;
        return $this;
    }
    
    /**
     * Adds additional metadata to the query.
     *
     * Sometimes a query may need to provide additional contextual data for the
     * alter hook. The alter hook implementations may then use that information
     * to decide if and how to take action.
     *
     * @param $key
     *   The unique identifier for this piece of metadata. Must be a string that
     *   follows the same rules as any other PHP identifier.
     * @param $object
     *   The additional data to add to the query. May be any valid PHP variable.
     *
     * @return EntityFieldQuery
     *   The called object.
     */
    public function addMetaData($key, $object) {
        $this->metaData[$key] = $object;
        return $this;
    }
    
    /**
     * Executes the query.
     *
     * After executing the query, $this->ordered_results will contain a list of
     * the same stub entities in the order returned by the query. This is only
     * relevant if there are multiple entity types in the returned value and
     * a field ordering was requested. In every other case, the returned value
     * contains everything necessary for processing.
     *
     * @return
     *   Either a number if count() was called or an array of associative arrays
     *   of stub entities. The outer array keys are entity types, and the inner
     *   array keys are the relevant ID. (In most cases this will be the entity
     *   ID. The only exception is when age=FIELD_LOAD_REVISION is used and field
     *   conditions or sorts are present -- in this case, the key will be the
     *   revision ID.) The entity type will only exist in the outer array if
     *   results were found. The inner array values are always stub entities, as
     *   returned by entity_create_stub_entity(). To traverse the returned array:
     *   @code
     *     foreach ($query->execute() as $entity_type => $entities) {
     *       foreach ($entities as $entity_id => $entity) {
     *   @endcode
     *   Note if the entity type is known, then the following snippet will load
     *   the entities found:
     *   @code
     *     $result = $query->execute();
     *     if (!empty($result[$my_type])) {
     *       $entities = entity_load($my_type, array_keys($result[$my_type]));
     *     }
     *   @endcode
     */
    public function execute() {
        // Give a chance to other modules to alter the query.
        drupal_alter('entity_query', $this);
        $this->altered = TRUE;
        // Initialize the pager.
        $this->initializePager();
        // Execute the query using the correct callback.
        $result = call_user_func($this->queryCallback(), $this);
        return $result;
    }
    
    /**
     * Determines the query callback to use for this entity query.
     *
     * @return
     *   A callback that can be used with call_user_func().
     */
    public function queryCallback() {
        // Use the override from $this->executeCallback. It can be set either
        // while building the query, or using hook_entity_query_alter().
        if (function_exists($this->executeCallback)) {
            return $this->executeCallback;
        }
        // If there are no field conditions and sorts, and no execute callback
        // then we default to querying entity tables in SQL.
        if (empty($this->fields)) {
            return array(
                $this,
                'propertyQuery',
            );
        }
        // If no override, find the storage engine to be used.
        foreach ($this->fields as $field) {
            if (!isset($storage)) {
                $storage = $field['storage']['module'];
            }
            elseif ($storage != $field['storage']['module']) {
                throw new EntityFieldQueryException(t("Can't handle more than one field storage engine"));
            }
        }
        if ($storage) {
            // Use hook_field_storage_query() from the field storage.
            return $storage . '_field_storage_query';
        }
        else {
            throw new EntityFieldQueryException(t("Field storage engine not found."));
        }
    }
    
    /**
     * Queries entity tables in SQL for property conditions and sorts.
     *
     * This method is only used if there are no field conditions and sorts.
     *
     * @return
     *   See EntityFieldQuery::execute().
     */
    protected function propertyQuery() {
        if (empty($this->entityConditions['entity_type'])) {
            throw new EntityFieldQueryException(t('For this query an entity type must be specified.'));
        }
        $entity_type = $this->entityConditions['entity_type']['value'];
        $entity_info = entity_get_info($entity_type);
        if (empty($entity_info['base table'])) {
            throw new EntityFieldQueryException(t('Entity %entity has no base table.', array(
                '%entity' => $entity_type,
            )));
        }
        $base_table = $entity_info['base table'];
        $base_table_schema = drupal_get_schema($base_table);
        $select_query = db_select($base_table);
        $select_query->addExpression(':entity_type', 'entity_type', array(
            ':entity_type' => $entity_type,
        ));
        // Process the property conditions.
        foreach ($this->propertyConditions as $property_condition) {
            $this->addCondition($select_query, $base_table . '.' . $property_condition['column'], $property_condition);
        }
        // Process the four possible entity condition.
        // The id field is always present in entity keys.
        $sql_field = $entity_info['entity keys']['id'];
        $id_map['entity_id'] = $sql_field;
        $select_query->addField($base_table, $sql_field, 'entity_id');
        if (isset($this->entityConditions['entity_id'])) {
            $this->addCondition($select_query, $base_table . '.' . $sql_field, $this->entityConditions['entity_id']);
        }
        // If there is a revision key defined, use it.
        if (!empty($entity_info['entity keys']['revision'])) {
            $sql_field = $entity_info['entity keys']['revision'];
            $select_query->addField($base_table, $sql_field, 'revision_id');
            if (isset($this->entityConditions['revision_id'])) {
                $this->addCondition($select_query, $base_table . '.' . $sql_field, $this->entityConditions['revision_id']);
            }
        }
        else {
            $sql_field = 'revision_id';
            $select_query->addExpression('NULL', 'revision_id');
        }
        $id_map['revision_id'] = $sql_field;
        // Handle bundles.
        if (!empty($entity_info['entity keys']['bundle'])) {
            $sql_field = $entity_info['entity keys']['bundle'];
            $having = FALSE;
            if (!empty($base_table_schema['fields'][$sql_field])) {
                $select_query->addField($base_table, $sql_field, 'bundle');
            }
        }
        else {
            $sql_field = 'bundle';
            $select_query->addExpression(':bundle', 'bundle', array(
                ':bundle' => $entity_type,
            ));
            $having = TRUE;
        }
        $id_map['bundle'] = $sql_field;
        if (isset($this->entityConditions['bundle'])) {
            if (!empty($entity_info['entity keys']['bundle'])) {
                $this->addCondition($select_query, $base_table . '.' . $sql_field, $this->entityConditions['bundle'], $having);
            }
            else {
                // This entity has no bundle, so invalidate the query.
                $select_query->where('1 = 0');
            }
        }
        // Order the query.
        foreach ($this->order as $order) {
            if ($order['type'] == 'entity') {
                $key = $order['specifier'];
                if (!isset($id_map[$key])) {
                    throw new EntityFieldQueryException(t('Do not know how to order on @key for @entity_type', array(
                        '@key' => $key,
                        '@entity_type' => $entity_type,
                    )));
                }
                $select_query->orderBy($id_map[$key], $order['direction']);
            }
            elseif ($order['type'] == 'property') {
                $select_query->orderBy($base_table . '.' . $order['specifier'], $order['direction']);
            }
        }
        return $this->finishQuery($select_query);
    }
    
    /**
     * Gets the total number of results and initializes a pager for the query.
     *
     * The pager can be disabled by either setting the pager limit to 0, or by
     * setting this query to be a count query.
     */
    function initializePager() {
        if ($this->pager && !empty($this->pager['limit']) && !$this->count) {
            $page = pager_find_page($this->pager['element']);
            $count_query = clone $this;
            $this->pager['total'] = $count_query->count()
                ->execute();
            $this->pager['start'] = $page * $this->pager['limit'];
            pager_default_initialize($this->pager['total'], $this->pager['limit'], $this->pager['element']);
            $this->range($this->pager['start'], $this->pager['limit']);
        }
    }
    
    /**
     * Finishes the query.
     *
     * Adds tags, metaData, range and returns the requested list or count.
     *
     * @param SelectQuery $select_query
     *   A SelectQuery which has entity_type, entity_id, revision_id and bundle
     *   fields added.
     * @param $id_key
     *   Which field's values to use as the returned array keys.
     *
     * @return
     *   See EntityFieldQuery::execute().
     */
    function finishQuery($select_query, $id_key = 'entity_id') {
        foreach ($this->tags as $tag) {
            $select_query->addTag($tag);
        }
        foreach ($this->metaData as $key => $object) {
            $select_query->addMetaData($key, $object);
        }
        $select_query->addMetaData('entity_field_query', $this);
        if ($this->range) {
            $select_query->range($this->range['start'], $this->range['length']);
        }
        if ($this->count) {
            return $select_query->countQuery()
                ->execute()
                ->fetchField();
        }
        $return = array();
        foreach ($select_query->execute() as $partial_entity) {
            $bundle = isset($partial_entity->bundle) ? $partial_entity->bundle : NULL;
            $entity = entity_create_stub_entity($partial_entity->entity_type, array(
                $partial_entity->entity_id,
                $partial_entity->revision_id,
                $bundle,
            ));
            $return[$partial_entity->entity_type][$partial_entity->{$id_key}] = $entity;
            $this->ordered_results[] = $partial_entity;
        }
        return $return;
    }
    
    /**
     * Adds a condition to an already built SelectQuery (internal function).
     *
     * This is a helper for hook_entity_query() and hook_field_storage_query().
     *
     * @param SelectQuery $select_query
     *   A SelectQuery object.
     * @param $sql_field
     *   The name of the field.
     * @param $condition
     *   A condition as described in EntityFieldQuery::fieldCondition() and
     *   EntityFieldQuery::entityCondition().
     * @param $having
     *   HAVING or WHERE. This is necessary because SQL can't handle WHERE
     *   conditions on aliased columns.
     */
    public function addCondition(SelectQuery $select_query, $sql_field, $condition, $having = FALSE) {
        $method = $having ? 'havingCondition' : 'condition';
        $like_prefix = '';
        switch ($condition['operator']) {
            case 'CONTAINS':
                $like_prefix = '%';
            case 'STARTS_WITH':
                $select_query->{$method}($sql_field, $like_prefix . db_like($condition['value']) . '%', 'LIKE');
                break;
            default:
                $select_query->{$method}($sql_field, $condition['value'], $condition['operator']);
        }
    }

}

/**
 * Defines an exception thrown when a malformed entity is passed.
 */
class EntityMalformedException extends Exception {

}