[1.8.x] Fixed #25233 -- Fixed HStoreField.has_changed() handling of initial values.

Thanks Simon Charette for review.

Backport of a7b7f27c05 from master

django/contrib/postgres/forms/hstore.py

@@ -23,6 +23,7 @@ class HStoreField(forms.CharField):
     def to_python(self, value):
         if not value:
             return {}
+        if not isinstance(value, dict):
             try:
                 value = json.loads(value)
             except ValueError:

docs/releases/1.8.4.txt

@@ -22,5 +22,5 @@ Bugfixes
 * Prevented an exception in ``TestCase.setUpTestData()`` from leaking the
   transaction (:ticket:`25176`).
 
-* Fixed ``has_changed()`` method in
-  :class:`django.contrib.postgres.forms.HStoreField`.
+* Fixed ``has_changed()`` method in ``contrib.postgres.forms.HStoreField``
+  (:ticket:`25215`, :ticket:`25233`).

tests/postgres_tests/test_hstore.py

@@ -196,6 +196,12 @@ class TestFormField(TestCase):
         form_w_hstore = HStoreFormTest({'f1': '{"a": 2}'}, initial={'f1': '{"a": 1}'})
         self.assertTrue(form_w_hstore.has_changed())
 
+        form_w_hstore = HStoreFormTest({'f1': '{"a": 1}'}, initial={'f1': {"a": 1}})
+        self.assertFalse(form_w_hstore.has_changed())
+
+        form_w_hstore = HStoreFormTest({'f1': '{"a": 2}'}, initial={'f1': {"a": 1}})
+        self.assertTrue(form_w_hstore.has_changed())
+
 
 class TestValidator(TestCase):