fix: duplicate active record objects on inverse_of

Fixes a bug that causes duplicate references to the same object to be
added to the collection association on an active_record object when
inverse_of is used.

In cases where has_many_inversing is set to true, the
set_inverse_instance function calls target= on collection_association during concat
resulting in multiple appends to target. This only occurs for new records. This
PR introduces changes that sets the index so the duplicate object
replaces the original.

Closes issue rails#43222.

Co-authored-by: Terence Li <[email protected]>
Co-authored-by: Dave Rose <[email protected]>

Author: 3 people

activerecord/lib/active_record/associations/collection_association.rb

@@ -456,6 +456,10 @@ def replace_on_target(record, skip_callbacks, replace:, inversing: false)
 
           yield(record) if block_given?
 
+          if !index && @replaced_or_added_targets.include?(record)
+            index = @target.index(record)
+          end
+
           @replaced_or_added_targets << record if inversing || index || record.new_record?
 
           if index

activerecord/test/cases/associations/inverse_associations_test.rb

@@ -766,6 +766,15 @@ def test_with_has_many_inversing_does_not_trigger_association_callbacks_on_set_w
     end
   end
 
+  def test_with_hash_many_inversing_does_not_add_duplicate_associated_objects
+    with_has_many_inversing(Interest) do
+      human = Human.new
+      interest = Interest.new(human: human)
+      human.interests << interest
+      assert_equal 1, human.interests.size
+    end
+  end
+
   def test_unscope_does_not_set_inverse_when_incorrect
     interest = interests(:trainspotting)
     human = interest.human