How to set composite key in Rails application

Question

I am using \'foriegner\' gem in my application to set primary key, now i am in a situation to set composite primary key in a table.

I searched the web for this, but

Answer 1

ActiveRecord

There is a gem called composite_primary_keys and integrates these features quite will for ActiveRecord.

It supports a wide array of ActiveRecord versions.

# Gemfile
gem 'composite_primary_keys', '='

Use it like the following example:

class Membership < ActiveRecord::Base
  self.primary_keys = :user_id, :group_id
end

membership = Membership.find([1,1])  # composite ids returns single instance
# => "1", "group_id"=>"1"}>

I am happily using it in production, keeping my schema clean and tidy.

Better alternative: Sequel

As always, if you are looking for a great Ruby + PostgreSQL solution, look no further than jeremyevans/sequel.

It comes with a vast amount of features, including composite primary keys. Out of the box.

So if you are starting a new project (on PostgreSQL obviously), save yourself the headache of ActiveRecord and go with Sequel.

class Post < Sequel::Model
  set_primary_key [:category, :title]
end