/**
* Compares two values and returns:
* -1 if the first value is less than the second.
* 1 if the first value is greater than the second.
* 0 if the two values are equivalent.
*
* @see http://docs.mongodb.org/manual/reference/operator/aggregation/cmp/
* @see Expr::cmp
* @param mixed|Expr $expression1
* @param mixed|Expr $expression2
* @return self
*/
public function cmp($expression1, $expression2)
{
$this->expr->cmp($expression1, $expression2);
return $this;
}
