Skip persisted through targets when autosaving collection associations

Author: joshuay03

activerecord/lib/active_record/autosave_association.rb

@@ -297,7 +297,15 @@ def init_internals
       # unless the parent is/was a new record itself.
       def associated_records_to_validate_or_save(association, new_record, autosave)
         if new_record || custom_validation_context?
-          association && association.target
+          target = association && association.target
+          if target && association.reflection.through_reflection
+            # We expect new through records to be autosaved by their direct parent.
+            # This prevents already persisted through records from being validated or saved
+            # more than once.
+            target.find_all(&:changed_for_autosave?)
+          else
+            target
+          end
         elsif autosave
           association.target.find_all(&:changed_for_autosave?)
         else

activerecord/test/cases/autosave_association_test.rb

@@ -40,6 +40,9 @@
 require "models/cake_designer"
 require "models/drink_designer"
 require "models/cpk"
+require "models/family"
+require "models/family_tree"
+require "models/user"
 
 class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
   def test_autosave_works_even_when_other_callbacks_update_the_parent_model
@@ -1147,6 +1150,34 @@ def test_autosave_new_record_with_after_create_callback_and_habtm_association
 
     assert_equal 1, post.categories.reload.length
   end
+
+  FamilyLoadingMiddleAndThroughRecordsBeforeSave = Class.new(Family) do
+    before_save do
+      family_trees.map(&:member) + members
+    end
+  end
+
+  def test_autosave_new_record_with_hmt_and_middle_record_built_by_parent
+    family = FamilyLoadingMiddleAndThroughRecordsBeforeSave.new
+    family_tree = family.family_trees.build
+    family_tree.build_member
+    family.save!
+    family.reload
+
+    assert_equal 1, family.family_trees.size
+    assert_equal 1, family.members.size
+  end
+
+  def test_autosave_new_record_with_hmt_and_middle_record_built_by_through_record
+    family = FamilyLoadingMiddleAndThroughRecordsBeforeSave.new
+    member = family.members.build
+    family.family_trees.build(member: member)
+    family.save!
+    family.reload
+
+    assert_equal 1, family.family_trees.size
+    assert_equal 1, family.members.size
+  end
 end
 
 class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase