Fix that has_one natural assignment to already associated record. [#854 state:resolved]

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activerecord/lib/active_record/associations/has_one_association.rb

@@ -21,8 +21,8 @@ module ActiveRecord
       def replace(obj, dont_save = false)
         load_target
 
-        unless @target.nil?
-          if dependent? && !dont_save && @target != obj
+        unless @target.nil? || @target == obj
+          if dependent? && !dont_save
             @target.destroy unless @target.new_record?
             @owner.clear_association_cache
           else

activerecord/test/cases/associations/has_one_associations_test.rb

@@ -79,6 +79,16 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     assert_raises(ActiveRecord::RecordNotFound) { Account.find(old_account_id) }
   end
 
+  def test_natural_assignment_to_already_associated_record
+    company = companies(:first_firm)
+    account = accounts(:signals37)
+    assert_equal company.account, account
+    company.account = account
+    company.reload
+    account.reload
+    assert_equal company.account, account
+  end
+
   def test_assignment_without_replacement
     apple = Firm.create("name" => "Apple")
     citibank = Account.create("credit_limit" => 10)