def initialize(db, fs_name=Grid::DEFAULT_FS_NAME)
raise MongoArgumentError, "db must be a Mongo::DB." unless db.is_a?(Mongo::DB)
@db = db
@files = @db["#{fs_name}.files"]
@chunks = @db["#{fs_name}.chunks"]
@fs_name = fs_name
@default_query_opts = {:sort => [['filename', 1], ['uploadDate', -1]], :limit => 1}
connection = @db.connection
begin
@files.ensure_index([['filename', 1], ['uploadDate', -1]])
@chunks.ensure_index([['files_id', Mongo::ASCENDING], ['n', Mongo::ASCENDING]], :unique => true)
rescue Mongo::ConnectionFailure
end
end