Multiple databases through a single connection MongoDB, GridFS I want to use GridFS in your project. As the main database using mongodb. 

My application can do only one connection to the database (such conditions). 

Can I make calls to other databases using the primary as a proxy?
Yes, I had the same issue. I use the db.getSiblingDB('yourdb') command in my scripts to make many calls to various databases. 

This is documented further at http://docs.mongodb.org/manual/reference/method/db.getSiblingDB/ .