Fixed an error triggered by a reload followed by a foreign key assignment.

Signed-off-by: NMichael Koziarski <michael@koziarski.com>

activerecord/lib/active_record/associations.rb

@@ -1268,7 +1268,11 @@ def association_accessor_methods(reflection, association_proxy_class)
 
           if association_proxy_class == BelongsToAssociation
             define_method("#{reflection.primary_key_name}=") do |target_id|
-              instance_variable_get(ivar).reset if instance_variable_defined?(ivar)
+              if instance_variable_defined?(ivar)
+                if association = instance_variable_get(ivar)
+                  association.reset
+                end
+              end
               write_attribute(reflection.primary_key_name, target_id)
             end
           end

activerecord/test/cases/associations_test.rb

@@ -194,6 +194,14 @@ def test_reset_loads_association_next_time
     assert_equal david, welcome.author
   end
 
+  def test_assigning_association_id_after_reload
+    welcome = posts(:welcome)
+    welcome.reload
+    assert_nothing_raised do
+      welcome.author_id = authors(:david).id
+    end
+  end
+
   def test_reload_returns_assocition
     david = developers(:david)
     assert_nothing_raised do