/** * Counts and returns the total the number of items in an array. * * The argument can be any expression as long as it resolves to an array. * * @see http://docs.mongodb.org/manual/reference/operator/aggregation/size/ * @see Expr::size * @param mixed|Expr $expression * @return self */ public function size($expression) { $this->expr->size($expression); return $this; }