What order do before filters occur in?

What order do before filters occur in? Specifically, what order do the before_action filters occur in, in regards to inheiritance? For example, will this work:

class A < ActionController::Base
  before_action :set_user

  def set_user
    @user = something
  end
end

class B < A
  before_action :set_post

  def show
    render @post
  end

  def set_post
    @post = @user.posts.first
  end
end

Will B#show work? What are the rules for filter order for future reference? I can't find any of this in the Rails documentation.

I suggest taking a look at the source code and API Docs on filters.

The default ordering should be

1. :set_post
2. :set_user

I think if you wanted to push :set_user to the top of the stack you could change the line in A to

prepend_before_action :set_user

Also worth pointing out, this isn't the only question on the topic; there are others here on SO.

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As for your specific situation, it looks like you'll need to change A as I mentioned above in order to have @user be assigned by the time set_post in B runs.

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As of 4.2.6 (probably changed in an earlier version), the ordering is now parent before child:

1. :set_user
2. :set_post