Support fixture associations for composite models

Most of the support here is in implementing how to correctly substitute
multiple values in place of one, for composite caes. In composite cases,
it's not sufficient to hash a label into a single integer value.
Instead, we build an API that accepts a single label, and a list of
columns that we'd like to map to. The algorithm used internally is very
similar to #identify, with an additional bit shift and modulo to cycle
the hash and ensure it doesn't exceed a max.

Author: paarthmadan

activerecord/lib/active_record/fixture_set/table_row.rb

@@ -125,13 +125,11 @@ def generate_primary_key
         end
 
         def generate_composite_primary_key
-          id = ActiveRecord::FixtureSet.identify(@label)
-          model_metadata.primary_key_name.each_with_index do |column, index|
+          composite_key = ActiveRecord::FixtureSet.composite_identify(@label, model_metadata.primary_key_name)
+          composite_key.each do |column, value|
             next if column_defined?(column)
-            raise "Automatic key generation assumes columns of type Integer." unless model_metadata.column_type(column) == :integer
 
-            # Shift label identifier index-#-of-times to differentiate sub-components in deterministic manner.
-            @row[column] = (id << index) % ActiveRecord::FixtureSet::MAX_ID
+            @row[column] = value
           end
         end
 
@@ -165,8 +163,17 @@ def resolve_sti_reflections
                   raise PrimaryKeyError.new(@label, association, value)
                 end
 
-                fk_type = reflection_class.type_for_attribute(fk_name).type
-                @row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
+                if fk_name.is_a?(Array)
+                  composite_key = ActiveRecord::FixtureSet.composite_identify(value, fk_name)
+                  composite_key.each do |column, value|
+                    next if column_defined?(column)
+
+                    @row[column] = value
+                  end
+                else
+                  fk_type = reflection_class.type_for_attribute(fk_name).type
+                  @row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
+                end
               end
             when :has_many
               if association.options[:through]

activerecord/lib/active_record/fixtures.rb

@@ -585,6 +585,18 @@ def identify(label, column_type = :integer)
         end
       end
 
+      # Returns a consistent, platform-independent hash representing a mapping
+      # between the label and the subcomponents of the provided composite key.
+      #
+      # Example:
+      # composite_identify("label", [:a, :b, :c]) => { a: hash_1, b: hash_2, c: hash_3 }
+      def composite_identify(label, key)
+        key
+          .index_with
+          .with_index { |sub_key, index| (identify(label) << index) % MAX_ID }
+          .with_indifferent_access
+      end
+
       # Superclass for the evaluation contexts used by ERB fixtures.
       def context_class
         @context_class ||= Class.new

activerecord/test/cases/fixtures_test.rb

@@ -1643,15 +1643,15 @@ def readonly_config
   end
 
   class CompositePkFixturesTest < ActiveRecord::TestCase
-    fixtures :cpk_orders, :cpk_books, :authors
+    fixtures :cpk_orders, :cpk_books, :cpk_authors, :cpk_reviews, :cpk_order_agreements
 
     def test_generates_composite_primary_key_for_partially_filled_fixtures
-      david = authors(:david)
-      david_cpk_book = cpk_books(:cpk_known_author_david_book)
+      alice = cpk_authors(:cpk_great_author)
+      alice_cpk_book = cpk_books(:cpk_great_author_first_book)
 
-      assert_not_empty(david_cpk_book.id.compact)
-      assert_equal david.id, david_cpk_book.author_id
-      assert_not_nil david_cpk_book.number
+      assert_not_empty(alice_cpk_book.id.compact)
+      assert_equal alice.id, alice_cpk_book.author_id
+      assert_not_nil alice_cpk_book.number
     end
 
     def test_generates_composite_primary_key_ids
@@ -1664,5 +1664,70 @@ def test_generates_composite_primary_key_ids
     def test_generates_composite_primary_key_with_unique_components
       assert_equal 2, cpk_orders(:cpk_groceries_order_1).id.uniq.size
     end
+
+    def test_resolves_associations_using_composite_primary_keys
+      review = cpk_reviews(:first_book_review)
+      generated_book = cpk_books(:cpk_book_with_generated_pk)
+
+      assert_equal generated_book.id, [review.author_id, review.number]
+      assert_equal generated_book, review.book
+    end
+
+    def test_resolves_associations_using_composite_primary_keys_with_partially_filled_values
+      review = cpk_reviews(:second_book_review_for_book_with_partial_pk_defined)
+      book_with_partially_filled_cpk = cpk_books(:cpk_great_author_first_book)
+
+      assert_equal book_with_partially_filled_cpk.id, [review.author_id, review.number]
+      assert_equal book_with_partially_filled_cpk, review.book
+    end
+
+    def test_association_with_custom_primary_key
+      order = cpk_orders(:cpk_groceries_order_2)
+      order_agreement = cpk_order_agreements(:order_agreement_three)
+
+      _, order_id = order.id
+
+      assert_equal order_id, order_agreement.order_id
+      assert_equal order, order_agreement.order
+    end
+
+    def test_composite_identify_resolves_to_same_values
+      identify_one = ActiveRecord::FixtureSet.composite_identify("label", [:a, :b, :c])
+      identify_two = ActiveRecord::FixtureSet.composite_identify("label", [:a, :b, :c])
+
+      assert_equal identify_one, identify_two
+    end
+
+    def test_composite_identify_returns_hash_with_key_names
+      id = ActiveRecord::FixtureSet.composite_identify("order", Cpk::Order.primary_key)
+
+      assert_equal ["shop_id", "id"], id.keys
+    end
+
+    def test_composite_identify_uses_same_hashing_algorithm_as_identify_for_first_attribute
+      id_hash = ActiveRecord::FixtureSet.composite_identify("order", [:first_attribute, :second_attribute])
+      id = ActiveRecord::FixtureSet.identify("order")
+
+      assert_equal id, id_hash[:first_attribute]
+      assert_not_equal id, id_hash[:second_attribute]
+    end
+
+    def test_composite_identify_hashes_one_label_to_same_values_irrespective_of_column_names
+      id_hash_one = ActiveRecord::FixtureSet.composite_identify("order", [:first_attribute, :second_attribute])
+      id_hash_two = ActiveRecord::FixtureSet.composite_identify("order", [:shop_id, :id])
+
+      assert_equal id_hash_one.values, id_hash_two.values
+      assert_not_equal id_hash_one.keys, id_hash_two.keys
+    end
+
+    def test_composite_identify_hashes_to_same_values_based_on_position_in_key
+      id = ActiveRecord::FixtureSet.identify("order")
+      id_hash_two = ActiveRecord::FixtureSet.composite_identify("order", [:one, :two])
+      id_hash_three = ActiveRecord::FixtureSet.composite_identify("order", [:one, :two, :three])
+
+      assert_equal id, id_hash_two.values.first
+      assert_equal id, id_hash_three.values.first
+      assert_equal id_has_two.values, id_hash_three.values.slice(0, 2)
+    end
   end
 end

activerecord/test/fixtures/cpk_books.yml

@@ -16,7 +16,6 @@ cpk_famous_author_first_book:
   title: "Ruby on Rails"
   revision: 1
 
-cpk_known_author_david_book:
-  author_id: 1
-  title: "David's CPK Book"
+cpk_book_with_generated_pk:
+  title: "Generated author's book"
   revision: 1

activerecord/test/fixtures/cpk_order_agreements.yml

@@ -6,3 +6,8 @@ order_agreement_one:
 
 order_agreement_two:
   signature: "xyz789"
+
+order_agreement_three:
+  order_id: <%= ActiveRecord::FixtureSet.composite_identify(:cpk_groceries_order_2, Cpk::Order.primary_key)[:id] %>
+  signature: "def321"
+

activerecord/test/fixtures/cpk_reviews.yml

@@ -0,0 +1,13 @@
+_fixture:
+  model_class: Cpk::Review
+
+first_book_review:
+  book: cpk_book_with_generated_pk
+  rating: 5
+  comment: "The first book was alright."
+
+second_book_review_for_book_with_partial_pk_defined:
+  book: cpk_great_author_first_book
+  author_id: <%= ActiveRecord::FixtureSet.identify(:cpk_great_author) %>
+  rating: 5
+  comment: "The first book was alright."

activerecord/test/models/cpk.rb

@@ -3,4 +3,5 @@
 require_relative "cpk/author"
 require_relative "cpk/book"
 require_relative "cpk/order"
+require_relative "cpk/review"
 require_relative "cpk/order_agreement"

activerecord/test/models/cpk/review.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Cpk
+  class Review < ActiveRecord::Base
+    self.table_name = :cpk_reviews
+
+    belongs_to :book, class_name: "Cpk::Book", query_constraints: [:author_id, :number]
+  end
+end

activerecord/test/schema/schema.rb

@@ -251,6 +251,13 @@
     t.string :name
   end
 
+  create_table :cpk_reviews, force: true do |t|
+    t.integer :author_id
+    t.integer :number
+    t.integer :rating
+    t.string :comment
+  end
+
   create_table :cpk_orders, primary_key: [:shop_id, :id], force: true do |t|
     t.integer :shop_id
     t.integer :id