rvm gemsets with Bundler

Question

Using Rails:

If Bundler retrieves the proper gems (and dependencies) and locks them in the Gemfile.lock for a given project, isn't using a gemset for this same project overkill? I've been told that using gemsets is still a good practice because merely having 2 versions of the same gem in your current PATH can cause conflicts. Is this right, or do you only need one or the other: Bundler or RVM?

Answer 1

It's redundant to use RVM's gemsets if you're using bundler.

Conflicts when using Bundler arise primarily for two reason:

1. Using gems that require other gems without precise version specifications.
2. Executable conflicts: you have both rails v3 and v4 installed, so where do we go to when calling rails g migration or calling rake?

The first issue can be resolved if you're careful about specifying your gem versions more explicitly in your Gemfile.

When working within a project with a Gemfile, the second issue can be resolved by prefixing executable calls with bundle exec, which will run the command within the context of the current bundle (e.g. bundle exec rake db:migrate).

When you want to specify a gem version outside of a Gemfile's context (e.g. rails new fancy_app), you can specify any gem's version by providing it as the first argument surrounded by underscores.

rake --version
rake _10.3.1_ --version
rails new rails_latest_app
rails _3.2.12_ new rails_3_app
rails _4.0.4_ new rails_4_app

RubyGems handles all of this for you by creating version-aware wrappers for any gem's executables. Just run cat `which gem_executable` (with gem_executable being something like rake, rails, foreman, pry, etc.) and have a look.

Stephen Ball has a good blog post about how to use Bundler instead of RVM gemsets, which explores the overlaps in further detail.

While RVM's gemsets are not necessary, RVM provides other conveniences:

• Automatically adding bundler binstubs to the PATH, so you can avoid typing bundle exec. Note the bundler plugin for oh-my-zsh provides the same feature
• Managing multiple Ruby versions

The ruby version manager rbenv provides similar features as well.

Answer 2

Yes, gemsets are overkill. Just use bundler.

RVM is still usefull for managing versions of Ruby itself - but don't use it for gemsets. Just use bundler for gem version management.

Regarding conflicts between gem versions, if you use bundle exec before each command you shouldn't have a problem - eg. bundle exec rake db:migrate or whatever.