PHP + Mongodb如何获得整个收藏？

How should I get whole collection from Mongodb which has about 10000 items by PHP script? I thought it is simple taks but it looks its not. I have this script to get all items from Mongodb:

public function setCadastralUnits()
{
    $this->cadastralUnits = [];
    $mongoCursor = $this->mongoCollection->find();

    foreach ( $mongoCursor as $unit )
    {
        $this->cadastralUnits[$unit->id] = $unit;
    }
}

But this trivial function which creates indexed array kills whole script. What is wrong with that?