Doctrine\MongoDB\Aggregation\Stage\Group::expression PHP Méthode

Used to use an expression as field value. Can be any expression

See also: http://docs.mongodb.org/manual/meta/aggregation-quick-reference/#aggregation-expressions

See also: Expr::expression

public expression ( mixed \| Expr $value )
$value	mixed \| Doctrine\MongoDB\Aggregation\Expr

    public function expression($value)
    {
        $this->expr->expression($value);
        return $this;
    }

Group