On the ServerGrove blog today there's a quick new post showing a method you can use to log the queries to your MongoDB database in your Symfony2-based application.
Symfony 2 comes with native support to connect to MongoDB using the DoctrineMongoDBBundle. Getting started is quite simple and there is not much that needs to be configured, but the manual does not say how to enable query logging although it is already possible with Symfony PR3. Query logging allows you to debug queries sent to the DB server by writing them in a log file. It is very useful for cases when you issue a query and you are not getting the results you expected.
The key is to add a "logger_class" value into your Symfony configuration file pointing to the "DoctrineMongoDBLogger" tool. The queries will then show up in your normal log files. They include a sample line along with a brief explanation of the values inside.