belongs_to association doesn't work with composite `primary_key` option about rails

[nvasilevski]

@Jay0921 While this should work as well, overriding primary_key is less preferable just because I find it semantically incorrect. I treat primary_key as a term coming from the db-level and I would prefer it to reflect the actual state of the database schema. This is why query_constraints is a little better option since it will behave as a "virtual primary key" while not making primary_key value misleading.

But ultimately I agree that there is a legit issue (limitation) in current Rails capabilities and it needs to be addressed

[nvasilevski]

Hey, I created a reproduction script (with a potential fix included) so we can be sure we are discussing the same model setup:

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails"
  # If you want to test against edge Rails replace the previous line with this:
  # gem "rails", github: "rails/rails", branch: "main"

  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :tickers, id: false, force: true do |t|
    t.integer :gvkey
    t.primary_key :iid
  end

  create_table :co_actions, id: false, force: true do |t|
    t.integer :gvkey
    t.primary_key :iid
  end
end

class Ticker < ActiveRecord::Base
  query_constraints :gvkey, :iid
end

class CoAction < ActiveRecord::Base
  belongs_to :ticker, query_constraints: [:gvkey, :iid]
end

class BugTest < Minitest::Test
  def test_association_stuff
    ticker = Ticker.create!(gvkey: 123)
    CoAction.create!(gvkey: 123, iid: ticker.iid)
    assert_equal ticker, CoAction.take.ticker
  end
end

While I think your situation may be considered as a limitation in Rails I just wanted to share that there is a high chance that by defining query_constraints :gvkey, :iid on the Ticker model you'll get the behavior you are looking for.
It will lead to the Ticker objects to be always referenced by two columns and models that belongs_to :ticker may need to explicitly set primary_key: :iid if they want to reference it by just one column but overall this should be a working solution to at least get you unblocked

[bguban]

Hey @nvasilevski. Thanks for the quick response. I think the problem is conceptual. With the singular primary/foreign keys I was able to specify both (primary and foreign) in the relation and override the primary_key defined in the class but now, with the composite primary key, I'm only able to specify the foreign_key in the relation but the primary key is always taken from the class.

Going back to the schema. The ticker model has its own singular primary key and it connects to other models (except co_action) using its own key. Here is the schema:

ActiveRecord::Schema.define do
  create_table :tickers, id: true, force: true do |t|
    t.integer :gvkey
    t.integer :iid
  end

  create_table :co_actions, id: true, force: true do |t|
    t.integer :gvkey
    t.integer :iid
  end
end

class Ticker < ActiveRecord::Base
  has_many :co_actions, primary_key: [:gvkey, :iid], foreign_key: [:gvkey, :iid]
end

class CoAction < ActiveRecord::Base
  belongs_to :ticker, query_constraints: [:gvkey, :iid], primary_key: [:gvkey, :iid]
end

class BugTest < Minitest::Test
  def test_association_stuff
    ticker = Ticker.create!(gvkey: 123, iid: 321)
    CoAction.create!(gvkey: 123, iid: 321)
    assert_equal ticker, CoAction.take.ticker
  end
end

I understand that the schema looks weird but the co_actions table is given by a 3rd party provider so I can't add a ticker_id column to it.

BTW I was able to patch it. I just override the relation's @association_primary_key right after adding the relation:

class CoAction < ActiveRecord::Base
  belongs_to :ticker, query_constraints: [:gvkey, :iid], primary_key: [:gvkey, :iid]
  reflections['ticker'].instance_variable_set(:@association_primary_key, ['gvkey', 'iid'])
end

[Jay0921]

@bguban I'm not sure if this will resolve the problem.

class Ticker < ActiveRecord::Base
  self.primary_key = [:gvkey, :iid]

  has_many :co_actions, query_constraints: [:gvkey, :iid]
end

class CoAction < ActiveRecord::Base
  self.primary_key = [:gvkey, :iid]

  belongs_to :ticker, query_constraints: [:gvkey, :iid]
end