/** * Subtracts two numbers to return the difference. The second argument is * subtracted from the first argument. * * The arguments can be any valid expression as long as they resolve to numbers and/or dates. * * @see http://docs.mongodb.org/manual/reference/operator/aggregation/subtract/ * @see Expr::subtract * @param mixed|Expr $expression1 * @param mixed|Expr $expression2 * @return self */ public function subtract($expression1, $expression2) { $this->expr->subtract($expression1, $expression2); return $this; }