Last Updated: 2025-10-25

I was working in a Ruby codebase where the constructor is called initialize. I was defining a class that inherited from ActiveModel::Base and used initialize in this sub-class: It caused weird effects.

Due to how heavily ActiveModel::Base uses the initialize method internally, defining an initialize method on a subclass (e.g. TutorSearch < ActiveModel::Base) — one that DOES NOT include super - will not behave correctly.

Lessons

• Avoid defining constructors on a subclass without using super

In the general case (not necessarily Rails), this is the way to go about things

  def initialize
    super

    customer_suff
  end

• Alternatively write custom constructors that do the extra work while delegating to the original initialize

  def self.build
    record = new
    record.foo = true
    record
  end
  

• Lastly available, use callbacks like after_initialize