AssociationCollection#include? working properly for objects added with build method [#3472 state:resolved]

activerecord/lib/active_record/associations/association_collection.rb

@@ -363,6 +363,7 @@ module ActiveRecord
 
       def include?(record)
         return false unless record.is_a?(@reflection.klass)
+        return include_in_memory?(record) if record.new_record?
         load_target if @reflection.options[:finder_sql] && !loaded?
         return @target.include?(record) if loaded?
         exists?(record)
@@ -554,6 +555,18 @@ module ActiveRecord
           args.first.kind_of?(Hash) || !(loaded? || @owner.new_record? || @reflection.options[:finder_sql] ||
                                          @target.any? { |record| record.new_record? } || args.first.kind_of?(Integer))
         end
+
+        def include_in_memory?(record)
+          if @reflection.is_a?(ActiveRecord::Reflection::ThroughReflection)
+            @owner.send(proxy_reflection.through_reflection.name.to_sym).map do |source|
+              source_reflection_target = source.send(proxy_reflection.source_reflection.name)
+              return true if source_reflection_target.respond_to?(:include?) ? source_reflection_target.include?(record) : source_reflection_target == record
+            end
+            false
+          else
+            @target.include?(record)
+          end
+        end
     end
   end
 end

activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb

@@ -858,4 +858,10 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     assert_equal new_developer.name, "Marcelo"
     assert_equal new_developer.salary, 90_000
   end
+
+  def test_include_method_in_has_and_belongs_to_many_association_should_return_true_for_instance_added_with_build
+    project = Project.new
+    developer = project.developers.build
+    assert project.developers.include?(developer)
+  end
 end

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -1267,4 +1267,10 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal new_comment.type, "SpecialComment"
     assert_equal new_comment.post_id, posts(:welcome).id
   end
+
+  def test_include_method_in_has_many_association_should_return_true_for_instance_added_with_build
+    post = Post.new
+    comment = post.comments.build
+    assert post.comments.include?(comment)
+  end
 end

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -435,4 +435,18 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal new_subscriber.nick, "marklazz"
     assert_equal new_subscriber.name, "Marcelo Giorgi"
   end
+
+  def test_include_method_in_association_through_should_return_true_for_instance_added_with_build
+    person = Person.new
+    reference = person.references.build
+    job = reference.build_job
+    assert person.jobs.include?(job)
+  end
+
+  def test_include_method_in_association_through_should_return_true_for_instance_added_with_nested_builds
+    author = Author.new
+    post = author.posts.build
+    comment = post.comments.build
+    assert author.comments.include?(comment)
+  end
 end