MongoMapper docs

Does anyone have a good resource for MongoMapper documentation? I've been reading through the mongoDB docs, but a 开发者_Python百科lot of it doesn't convert across to ruby/mm. I've been trying to figure out how to do a SELECT FROM WHERE EXISTS with little success.

db.things.find( { a : { $exists : true } } ); // return object if a is present

The only docs I've found so far these which have helped a little.

Thanks.

Here is the three good pdf link which will guide you how to store files,retrieve files,twitter schema,followers, insert,update and many more..........

First Pdf - MongoDb by Kristina

MongoDb by Kyle

MongoDb by Mathias Stearn

Actually, there's a documentation project now: http://mongomapper.com/documentation/