interface SelectionInterface

interface SelectionInterface extends PluginFormInterface {
    
    /**
     * Gets the list of referenceable entities.
     *
     * @param string|null $match
     *   (optional) Text to match the label against. Defaults to NULL.
     * @param string $match_operator
     *   (optional) Operator to be used for string matching. Defaults to
     *   "CONTAINS".
     * @param int $limit
     *   (optional) Limit the query to a given number of items. Defaults to 0,
     *   which indicates no limiting.
     *
     * @return array
     *   A nested array of entities, the first level is keyed by the
     *   entity bundle, which contains an array of entity labels (escaped),
     *   keyed by the entity ID.
     */
    public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0);
    
    /**
     * Counts entities that are referenceable.
     *
     * @param string $match
     *   (optional) Text to match the label against. Defaults to NULL.
     * @param string $match_operator
     *   (optional) Operator to be used for string matching. Defaults to
     *   "CONTAINS".
     *
     * @return int
     *   The number of referenceable entities.
     */
    public function countReferenceableEntities($match = NULL, $match_operator = 'CONTAINS');
    
    /**
     * Validates which existing entities can be referenced.
     *
     * @param array $ids
     *   An array of IDs to validate.
     *
     * @return array
     *   An array of valid entity IDs.
     */
    public function validateReferenceableEntities(array $ids);
    
    /**
     * Allows the selection to alter the SelectQuery generated by EntityFieldQuery.
     *
     * @param \Drupal\Core\Database\Query\SelectInterface $query
     *   A Select Query object.
     */
    public function entityQueryAlter(SelectInterface $query);

}