Fix problem where wrong keys are used in JoinAssociation when an association goes :through a belongs_to [#2801 state:resolved]

activerecord/lib/active_record/associations/class_methods/join_dependency/join_association.rb

@@ -190,17 +190,20 @@ module ActiveRecord
             ).alias @aliased_join_table_name
 
             jt_conditions = []
-            jt_foreign_key = first_key = second_key = nil
+            first_key = second_key = nil
 
-            if through_reflection.options[:as] # has_many :through against a polymorphic join
-              as_key         = through_reflection.options[:as].to_s
-              jt_foreign_key = as_key + '_id'
-
-              jt_conditions <<
-              join_table[as_key + '_type'].
-                eq(parent.active_record.base_class.name)
+            if through_reflection.macro == :belongs_to
+              jt_primary_key = through_reflection.primary_key_name
+              jt_foreign_key = through_reflection.association_primary_key
             else
+              jt_primary_key = through_reflection.active_record_primary_key
               jt_foreign_key = through_reflection.primary_key_name
+
+              if through_reflection.options[:as] # has_many :through against a polymorphic join
+                jt_conditions <<
+                join_table["#{through_reflection.options[:as]}_type"].
+                  eq(parent.active_record.base_class.name)
+              end
             end
 
             case source_reflection.macro
@@ -233,7 +236,7 @@ module ActiveRecord
             end
 
             jt_conditions <<
-            parent_table[parent.primary_key].
+            parent_table[jt_primary_key].
               eq(join_table[jt_foreign_key])
 
             if through_reflection.options[:conditions]

activerecord/lib/active_record/reflection.rb

@@ -208,6 +208,10 @@ module ActiveRecord
         @association_foreign_key ||= options[:association_foreign_key] || class_name.foreign_key
       end
 
+      def association_primary_key
+        @association_primary_key ||= options[:primary_key] || klass.primary_key
+      end
+
       def active_record_primary_key
         @active_record_primary_key ||= options[:primary_key] || active_record.primary_key
       end

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -479,4 +479,11 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, mary.unique_categorized_posts.length
     assert_equal 1, mary.unique_categorized_post_ids.length
   end
+
+  def test_joining_has_many_through_belongs_to
+    posts = Post.joins(:author_categorizations).
+                 where('categorizations.id' => categorizations(:mary_thinking_sti).id)
+
+    assert_equal [posts(:eager_other)], posts
+  end
 end

activerecord/test/cases/reflection_test.rb

@@ -191,6 +191,11 @@ class ReflectionTest < ActiveRecord::TestCase
     assert_kind_of ThroughReflection, Subscriber.reflect_on_association(:books)
   end
 
+  def test_association_primary_key
+    assert_equal "id", Author.reflect_on_association(:posts).association_primary_key.to_s
+    assert_equal "name", Author.reflect_on_association(:essay).association_primary_key.to_s
+  end
+
   def test_active_record_primary_key
     assert_equal "nick", Subscriber.reflect_on_association(:subscriptions).active_record_primary_key.to_s
     assert_equal "name", Author.reflect_on_association(:essay).active_record_primary_key.to_s

activerecord/test/models/post.rb

@@ -38,6 +38,7 @@ class Post < ActiveRecord::Base
   end
 
   has_many :author_favorites, :through => :author
+  has_many :author_categorizations, :through => :author, :source => :categorizations
 
   has_many :comments_with_interpolated_conditions, :class_name => 'Comment',
       :conditions => ['#{"#{aliased_table_name}." rescue ""}body = ?', 'Thank you for the welcome']