Fix has_many :through when the source is a belongs_to association. [#323 state:resolved]

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activerecord/lib/active_record/association_preload.rb

@@ -4,6 +4,28 @@ module ActiveRecord
       base.extend(ClassMethods)
     end
 
+    class HasManyAssociationStrategy
+      def initialize(through_reflection)
+        @through_reflection = through_reflection
+      end
+
+      def primary_key
+        if @through_reflection && @through_reflection.macro == :belongs_to
+          @through_reflection.klass.primary_key
+        else
+          @through_reflection.primary_key_name
+        end
+      end
+
+      def primary_key_name
+        if @through_reflection && @through_reflection.macro == :belongs_to
+          @through_reflection.primary_key_name
+        else
+          nil
+        end
+      end
+    end
+
     module ClassMethods
 
       # Loads the named associations for the activerecord record (or records) given
@@ -77,12 +99,13 @@ module ActiveRecord
         end
       end
 
-      def construct_id_map(records)
+      def construct_id_map(records, primary_key=nil)
         id_to_record_map = {}
         ids = []
         records.each do |record|
-          ids << record.id
-          mapped_records = (id_to_record_map[record.id.to_s] ||= [])
+          primary_key ||= record.class.primary_key
+          ids << record[primary_key]
+          mapped_records = (id_to_record_map[ids.last.to_s] ||= [])
           mapped_records << record
         end
         ids.uniq!
@@ -129,23 +152,24 @@ module ActiveRecord
       end
 
       def preload_has_many_association(records, reflection, preload_options={})
-        id_to_record_map, ids = construct_id_map(records)
-        records.each {|record| record.send(reflection.name).loaded}
         options = reflection.options
+        through_reflection = reflections[options[:through]]
+        strat = HasManyAssociationStrategy.new(through_reflection)
+        id_to_record_map, ids = construct_id_map(records, strat.primary_key_name)
+        records.each {|record| record.send(reflection.name).loaded}
 
         if options[:through]
           through_records = preload_through_records(records, reflection, options[:through])
           through_reflection = reflections[options[:through]]
-          through_primary_key = through_reflection.primary_key_name
           unless through_records.empty?
             source = reflection.source_reflection.name
-            #add conditions from reflection!
-            through_records.first.class.preload_associations(through_records, source, reflection.options)
+            through_records.first.class.preload_associations(through_records, source, options)
             through_records.each do |through_record|
-              add_preloaded_records_to_collection(id_to_record_map[through_record[through_primary_key].to_s],
-                                                 reflection.name, through_record.send(source))
+              through_record_id = through_record[strat.primary_key].to_s
+              add_preloaded_records_to_collection(id_to_record_map[through_record_id], reflection.name, through_record.send(source))
             end
           end
+
         else
           set_association_collection_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options),
                                              reflection.primary_key_name)

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -32,6 +32,14 @@ module ActiveRecord
       end
       
       protected
+        def target_reflection_has_associated_record?
+          if @reflection.through_reflection.macro == :belongs_to && @owner[@reflection.through_reflection.primary_key_name].blank?
+            false
+          else
+            true
+          end
+        end
+
         def construct_find_options!(options)
           options[:select]  = construct_select(options[:select])
           options[:from]  ||= construct_from
@@ -61,6 +69,7 @@ module ActiveRecord
         end
 
         def find_target
+          return [] unless target_reflection_has_associated_record?
           @reflection.klass.find(:all,
             :select     => construct_select,
             :conditions => construct_conditions,
@@ -102,6 +111,8 @@ module ActiveRecord
               "#{as}_type" => reflection.klass.quote_value(
                 @owner.class.base_class.name.to_s,
                 reflection.klass.columns_hash["#{as}_type"]) }
+          elsif reflection.macro == :belongs_to
+            { reflection.klass.primary_key => @owner[reflection.primary_key_name] }
           else
             { reflection.primary_key_name => owner_quoted_id }
           end

activerecord/test/cases/associations/eager_test.rb

@@ -275,6 +275,15 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_equal authors(:david), assert_no_queries { posts_with_comments_and_author.first.author }
   end
 
+  def test_eager_with_has_many_through_a_belongs_to_association
+    author = authors(:mary)
+    post = Post.create!(:author => author, :title => "TITLE", :body => "BODY")
+    author.author_favorites.create(:favorite_author_id => 1)
+    author.author_favorites.create(:favorite_author_id => 2)
+    posts_with_author_favorites = author.posts.find(:all, :include => :author_favorites)
+    assert_no_queries { posts_with_author_favorites.first.author_favorites.first.author_id }
+  end
+
   def test_eager_with_has_many_through_an_sti_join_model
     author = Author.find(:first, :include => :special_post_comments, :order => 'authors.id')
     assert_equal [comments(:does_it_hurt)], assert_no_queries { author.special_post_comments }

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -1081,3 +1081,4 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
 end
+

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -5,7 +5,7 @@ require 'models/reader'
 require 'models/comment'
 
 class HasManyThroughAssociationsTest < ActiveRecord::TestCase
-  fixtures :posts, :readers, :people, :comments
+  fixtures :posts, :readers, :people, :comments, :authors
 
   def test_associate_existing
     assert_queries(2) { posts(:thinking);people(:david) }
@@ -229,4 +229,19 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       end
     end
   end
+
+  def test_has_many_association_through_a_belongs_to_association_where_the_association_doesnt_exist
+    author = authors(:mary)
+    post = Post.create!(:title => "TITLE", :body => "BODY")
+    assert_equal [], post.author_favorites
+  end
+
+  def test_has_many_association_through_a_belongs_to_association
+    author = authors(:mary)
+    post = Post.create!(:author => author, :title => "TITLE", :body => "BODY")
+    author.author_favorites.create(:favorite_author_id => 1)
+    author.author_favorites.create(:favorite_author_id => 2)
+    author.author_favorites.create(:favorite_author_id => 3)
+    assert_equal post.author.author_favorites, post.author_favorites
+  end
 end

activerecord/test/models/post.rb

@@ -22,6 +22,8 @@ class Post < ActiveRecord::Base
     end
   end
 
+  has_many :author_favorites, :through => :author
+
   has_many :comments_with_interpolated_conditions, :class_name => 'Comment',
       :conditions => ['#{"#{aliased_table_name}." rescue ""}body = ?', 'Thank you for the welcome']