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.
$key: The unique identifier for this piece of metadata. Must be a string that follows the same rules as any other PHP identifier.
$object: The additional data to add to the query. May be any valid PHP variable.
EntityFieldQuery The called object.
public function addMetaData($key, $object) {
$this->metaData[$key] = $object;
return $this;
}