Merge pull request rails#29593 from kratob/master

ActiveRecord: do not create "has many through" records that have been removed

activerecord/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Previously, when building records using a `has_many :through` association,
+    if the child records were deleted before the parent was saved, they would
+    still be persisted. Now, if child records are deleted before the parent is saved
+    on a `has_many :through` association, the child records will not be persisted.
+
+    *Tobias Kraze*
+
+
 ## Rails 5.1.2 (June 26, 2017) ##
 
 *   Restore previous behavior of collection proxies: their values can have

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -109,6 +109,11 @@ def build_record(attributes)
           record
         end
 
+        def remove_records(existing_records, records, method)
+          super
+          delete_through_records(records)
+        end
+
         def target_reflection_has_associated_record?
           !(through_reflection.belongs_to? && owner[through_reflection.foreign_key].blank?)
         end

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -337,6 +337,17 @@ def test_build_then_save_with_has_one_inverse
     assert_includes post.single_people, person
   end
 
+  def test_build_then_remove_then_save
+    post = posts(:thinking)
+    post.people.build(first_name: "Bob")
+    ted = post.people.build(first_name: "Ted")
+    post.people.delete(ted)
+    post.save!
+    post.reload
+
+    assert_equal ["Bob"], post.people.collect(&:first_name)
+  end
+
   def test_both_parent_ids_set_when_saving_new
     post = Post.new(title: "Hello", body: "world")
     person = Person.new(first_name: "Sean")