Codeigniter + MongoDB

[eluser]gh0st[/eluser]
I'm trying to get the get_where command to work, but it never returns anything despite there being records to the contary;

Code:

$results = $this->mongo_db->get_where('company', array('cash' => 50000));

This should return at least 3 companies where their cash is 50000 but it always returns an empty array.

If I do:

Code:

$results = $this->mongo_db->get('company');

This will return all companies. So Mongo is installed and working.

What am I doing wrong?