Better Understand the MongoDB Structure

Perhaps a snippet should be included in the documentation, but when moving from an SQL oriented DB to MongoDB what is the proper drupal way to migrate queries in custom modules with this modules default setup. Pardon my novice understanding of MongoDB.

For example take a basic query that returns a list of all fields within a specified entity bundle:

<?php
$result = db_query('SELECT field_name FROM {field_config_instance} WHERE bundle = :bundle', array(':bundle' => $field_collection));
?>

What is the appropriate MongoDB translation when using this module? Perhaps something like:

<?php db.field_config_instance.find( <bundle = $field_collection>, <field_name> )
?>