MongodB查找fieldvalue> other fieldvalue * 0.5的位置

Question

I'm using the php manual examples for mangodb like below

$where=array( '$and' => array( array(' class' =>12), array('marks'=>70) ) );
$cursor = $collection->find($where);

I have two fields: population and male_population Is it possible to do a search where male_population is greater than 50%? I tried the below but it doesn't seem to work

$where['$and'][] = ['male_population' => ['$gt' => 1000]];
$where['$and'][] = ['male_population' => ['$gt' => 'this.population*0.5']];
$cursor = $collection->find($where);

also tried

$where['$and'][] = "this.male_population/this.population >= 0.5"

Answer 1

I found the solution

$where['$and'][] = ['$where' => "this.$male_population/this.population >= 0.5"]