Rails Before Concern
The Rails source code has changed a lot through the years, but some basic ideas haven’t changed much. One of these is the concept behind ActiveRecord::Base. As you’ve seen in ActiveRecord::Base, this class is an assembly of dozens of modules that define both instance methods and class methods. For example, Base includes ActiveRecord::Validations, and in the process it gets instance and class methods.
The mechanism that rolls those methods into Base, however, has changed. Let’s see how it worked in the beginning.
The Include-and-Extend Trick
Around the times of Rails 2, all validation methods were defined in ActiveRecord::Validations. (Back then, there was no Active Model library.) However, Validations pulled a peculiar ...
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