Ruby on Rails: Get nested modules?

Question

In my Rails project I want to get all modules that are nested inside the module A.

The file lib/assets/a/b.rb, consists of:

module A
  module B
  end
end

In the Rails console:

A.constants
  => []
A::B.class
  => Module
A.constants
  => [:B]

Why is the first line returning an empty array, and how do I get round the problem?

Ana María Martínez Gómez · Accepted Answer · 2017-12-04 15:47:00Z

1

That's because how Rails autoloading works.

When you call A.constants Rails find A in the a.rb file and get you the constants defined there. As it seems you didn't define any constant there, it is the empty array.

When you call A::B.class Rails autoloading looks for A::B and load a/b.rb. So, next time you call A.constants it returns the constants defined in both a.rb and a/b.rb, as both files are now loaded. And that's why it returns B the second time.

So, you can not solve the problem. This is expected as it is caused by how the Rails autoloading works.

Also, you say that your models are in lib/assets/, but this makes no difference, as it would be the same if they were in models/.

answered Dec 4, 2017 at 15:47

Ana María Martínez Gómez

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2 Comments

Vorpulus Lyphane Over a year ago

I'm afraid there is no a.rb file, so this isn't the answer. Everything you need to replicate what I did in the Rails console is in the question (i.e., the folder 'a', with the file 'b.rb' as shown).

Ana María Martínez Gómez Over a year ago

But the reason is the same, A::B is not loaded. You may want to read: guides.rubyonrails.org/autoloading_and_reloading_constants.html

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