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composite_primary_keys

⚙️ Implement Composite Primary Keys​

Rails doesn’t support composite primary keys out of the box, but you can include the composite_primary_keys gem and configure your model to use multiple columns as a key. This is critical when you have legacy tables or join tables without single id columns.

# Gemfile
gem 'composite_primary_keys'

# app/models/enrollment.rb
class Enrollment < ApplicationRecord
  self.primary_keys = :student_id, :course_id
  belongs_to :student
  belongs_to :course
end

With self.primary_keys, ActiveRecord operations (find, update, destroy) will correctly handle the composite key for your high‑volume lookup tables.