mongo-ruby-driver/docs/1.0_UPGRADE.md

You can upgrade freely from v0.20 to v1.0.

However, if you're running a version < 0.20, upgrade to 0.20 before upgrading to 1.0.

The upgrade to 0.20 requires some minor code upgrades.

1. Note the exception changes in HISTORY. Certain exceptions are now scoped under the BSON module; if you're catching these, you will need to modify your code.

2. The BSON types are now scoped under the BSON module.

3. Note that mongo_ext no longer exists. The new gems are bson and bson_ext.

4. Indexes on GridFS chunks collections should be unique. If you have existing GridFS collections, you should drop the current index and replace with a unique one. Before you do this, make sure that index doesn't exist; no need to go through process unnecessarily. If you do need to create the index, once you have the chunks collection, here are the commands you can run:

   @chunks.drop_index('files_id_1_n_1') @chunks.create_index('files_id', Mongo::ASCENDING], ['n', Mongo::ASCENDING, :unique => true)