Question

In ruby using the mongo gem I can’t find any documentation on how to find on a filename with GridFs.

Answer 1

First get a connection to the database, we’ll call this db. Then you can connect to your GridFS as a Mongo::Grid or Mongo::GridFileSystem instance:

fs = Mongo::Grid.new(db)
fs = Mongo::GridFileSystem.new(db)

Now you can use the Mongo::GridExt::InstanceMethods methods on fs. In particular, you can use exist?:

f = fs.exist? :filename => 'pancakes.png'

The exist? method is poorly named as it gives you a Hash if it finds something and a nil if it doesn’t.

That’s not terribly useful if you’re searching for, say, all filenames that match /pancakes/. However, GridFS is just a pair of normal MongoDB collections:

• fs.files: the file metadata.
• fs.chunks: the file data (in chunks).

If you want to do arbitrary metadata searches then you just need to get your hands on fs.files and have your way with it:

fs     = db['fs.files']
cursor = fs.find(:filename => /pancakes/)
# Now iterate through cursor or .count it or ...

The fs above will be a Mongo::Collection so its find method accepts all the usual query options.