public function embed(&$collection, $options = []) {
		$keys = $this->key();

		if (count($keys) !== 1) {
			throw new Exception("The embedding doesn't support composite primary key.");
		}

		switch($this->type()) {
			case 'belongsTo';
				return $this->_embedBelongsTo($collection, $options);
			case 'hasMany';
				if ($this->link() === static::LINK_KEY_LIST) {
					return $this->_embedHasManyAsList($collection, $options);
				}
				return $this->_embedHasMany($collection, $options);
			case 'hasOne';
				return $this->_embedHasOne($collection, $options);
			default:
				throw new Exception("Error {$this->type()} is unsupported ");
		}
	}