Provide a slightly more robust we_can_set_the_inverse_on_this? method…

… for polymorphic belongs_to associations. [#3520 state:resolved]

Also add a new test for polymorphic belongs_to that test direct accessor assignment, not just .replace assignment.

Signed-off-by: Eloy Duran <eloy.de.enige@gmail.com>

activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb

@@ -27,7 +27,12 @@ def updated?
         # NOTE - for now, we're only supporting inverse setting from belongs_to back onto
         # has_one associations.
         def we_can_set_the_inverse_on_this?(record)
-          @reflection.has_inverse? && @reflection.polymorphic_inverse_of(record.class).macro == :has_one
+          if @reflection.has_inverse?
+            inverse_association = @reflection.polymorphic_inverse_of(record.class)
+            inverse_association && inverse_association.macro == :has_one
+          else
+            false
+          end
         end
 
         def set_inverse_instance(record, instance)
@@ -52,7 +57,7 @@ def find_target
             else
               association_class.find(@owner[@reflection.primary_key_name], :select => @reflection.options[:select], :include => @reflection.options[:include])
             end
-          set_inverse_instance(target, @owner) if target
+          set_inverse_instance(target, @owner)
           target
         end
 

activerecord/test/cases/associations/inverse_associations_test.rb

@@ -480,7 +480,22 @@ def test_eager_loaded_child_instance_should_be_shared_with_parent_on_find
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to parent-owned instance"
   end
 
-  def test_child_instance_should_be_shared_with_replaced_parent
+  def test_child_instance_should_be_shared_with_replaced_via_accessor_parent
+    face = faces(:confused)
+    old_man = face.polymorphic_man
+    new_man = Man.new
+
+    assert_not_nil face.polymorphic_man
+    face.polymorphic_man = new_man
+
+    assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same before changes to parent instance"
+    face.description = 'Bongo'
+    assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same after changes to parent instance"
+    new_man.polymorphic_face.description = 'Mungo'
+    assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same after changes to replaced-parent-owned instance"
+  end
+
+  def test_child_instance_should_be_shared_with_replaced_via_method_parent
     face = faces(:confused)
     old_man = face.polymorphic_man
     new_man = Man.new