what's the difference between bundle.setup and bundle.require

Question

From the gemfile man page, I learned there are two ways to import the gems you specified in the Gemfile. The bundle.setup will "setup adds gems to Ruby's load path" while bundle.require will require all the gems.

What's the difference between these two methods? In which condition should I use one of them?

Answer 1

Bundler.setup modifies the LOAD_PATH, so you can do things like require 'some_gem' and they will work. It allows you to require gems 'by hand'. Before Bundler, using Rubygems, you would achieve much of the same effect doing require 'rubygems'.

Bundler.require(:default) on the other hand actually requires all the gems in the Gemfile (assuming you're not using groups; otherwise it requires those in the specified groups if you provide arguments). It is a shorthand for a bunch of require 'some_gem' statements.

See http://gembundler.com/rationale.html. Note that they say you have to do require 'bundler/setup' before doing Bundler.require, but in practice this usually is not necessary. I almost never use Bundler.setup (or require 'bundler/setup), because I require all gems via Bundler.require).

Answer 2

You must use Bundle.setup and you can use Bundle.require.

The main point of bundler is to make sure that exactly the Gems defined in the Gemfile are made visible to the application, i.e. all the gems mentioned there in exactly the mentioned versions, but not one more. To do that, the load path is adapted. This is done by Bundle.setup.

To actually use the gems, they have to be required and thus loaded into the application. This can either be done by hand using a number of require statements or automatically for all the gems listed in the Gemfile (or only some groups) using Bundle.require. This however is only possible after adapting the loadpath as mentioned above.