Posted about 10 years ago. Visible to the public.

Deal with error: Expected foo_trait.rb to define FooTrait

Lately, I came across a nasty error. I had a class Article that included FooTrait and BarTrait. In BarTrait, I then accidentally called a non-existent method:

has_defaults :dummy => Dummy.non_existent_method

From that moment, no page would load anymore but always display an exception: Expected foo_trait.rb to define FooTrait. That trait had nothing to do with BarTrait.

Since it doesn't tell you what's wrong, you either remember where you were working last or you need to check all traits Archive for mistakes.

This behavior is likely to be caused by Rails' autoloading.

Does your version of Ruby on Rails still receive security updates?
Rails LTS provides security patches for unsupported versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2).

Owner of this card:

Dominik Schöler
Last edit:
about 10 years ago
About this deck:
We are makandra and do test-driven, agile Ruby on Rails software development.
License for source code
Posted by Dominik Schöler to makandra dev
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