How to update single rails engine (gem) within a rails app?

Question

There are multi rails engines (gem) in our rails 3.2.12 app. When there is an update to a rails engine, the version is updated as well. Then bundle update engine_name to update the engine. However when bundle update engine_name, there is an error about ActiveModel which is not supposed to be updated. What's the right way to update a single rails engine gem?

Answer 1

bundle update --source=engine_name

This will update only your 'engine_name' from source, and will try to use versions of all other gems as defined in Gemfile.lock already.