Merge pull request rails#42448 from eileencodes/fix-has_one-with-has_many-disable_joins

Fix disable_joins when join foreign key is not ID

Author: eileencodes

activerecord/lib/active_record/associations/disable_joins_association_scope.rb

@@ -16,7 +16,8 @@ def scope(association)
 
       private
         def last_scope_chain(reverse_chain, owner)
-          first_scope = [reverse_chain.shift, false, [owner.id]]
+          first_item = reverse_chain.shift
+          first_scope = [first_item, false, [owner._read_attribute(first_item.join_foreign_key)]]
 
           reverse_chain.inject(first_scope) do |(reflection, ordered, join_ids), next_reflection|
             key = reflection.join_primary_key

activerecord/test/cases/associations/has_one_through_disable_joins_associations_test.rb

@@ -4,9 +4,13 @@
 require "models/member"
 require "models/member_detail"
 require "models/organization"
+require "models/project"
+require "models/developer"
+require "models/company"
+require "models/computer"
 
 class HasOneThroughDisableJoinsAssociationsTest < ActiveRecord::TestCase
-  fixtures :members, :organizations
+  fixtures :members, :organizations, :projects, :developers, :companies
 
   def setup
     @member = members(:groucho)
@@ -40,4 +44,21 @@ def test_preload_on_disable_joins_through
     assert_no_queries { members[0].organization }
     assert_no_queries { members[0].organization_without_joins }
   end
+
+  def test_has_one_through_with_belongs_to_on_disable_joins
+    firm = Firm.create!(name: "Adequate Holdings")
+    project = Project.create!(name: "Project 1", firm: firm)
+    Developer.create!(name: "Gorbypuff", firm: firm)
+
+    joins = capture_sql { project.lead_developer }
+    no_joins = capture_sql { project.lead_developer_disable_joins }
+
+    assert_equal project.lead_developer, project.lead_developer_disable_joins
+    assert_equal 2, no_joins.count
+    assert_equal 1, joins.count
+    assert_match(/INNER JOIN/, joins.first)
+    no_joins.each do |nj|
+      assert_no_match(/INNER JOIN/, nj)
+    end
+  end
 end

activerecord/test/models/project.rb

@@ -16,6 +16,7 @@ class Project < ActiveRecord::Base
   has_and_belongs_to_many :well_paid_salary_groups, -> { group("developers.salary").having("SUM(salary) > 10000").select("SUM(salary) as salary") }, class_name: "Developer"
   belongs_to :firm
   has_one :lead_developer, through: :firm, inverse_of: :contracted_projects
+  has_one :lead_developer_disable_joins, through: :firm, inverse_of: :contracted_projects, source: :lead_developer, disable_joins: true
 
   begin
     previous_value, ActiveRecord::Base.belongs_to_required_by_default =