From 62c19a21b65985b9d54eb1c5a1cf747fe7a54c84 Mon Sep 17 00:00:00 2001
From: Andrea Grandi <a.grandi@gmail.com>
Date: Sun, 24 May 2015 15:56:48 +0100
Subject: [PATCH] Fixed #24844 -- Corrected has_changed implementation for
 HStoreField.

Backport of 43b2d88a5b9cfb151ccf7ac861f2750e70c0e2c4 from master
---
 django/contrib/postgres/forms/hstore.py | 10 ++++++++++
 docs/releases/1.8.3.txt                 |  4 +++-
 tests/postgres_tests/test_hstore.py     |  7 +++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/django/contrib/postgres/forms/hstore.py b/django/contrib/postgres/forms/hstore.py
index 2c564ea53c..a138093e90 100644
--- a/django/contrib/postgres/forms/hstore.py
+++ b/django/contrib/postgres/forms/hstore.py
@@ -34,3 +34,13 @@ class HStoreField(forms.CharField):
         for key, val in value.items():
             value[key] = six.text_type(val)
         return value
+
+    def has_changed(self, initial, data):
+        """
+        Return True if data differs from initial.
+        """
+        # For purposes of seeing whether something has changed, None is
+        # the same as an empty dict, if the data or initial value we get
+        # is None, replace it w/ {}.
+        initial_value = self.to_python(initial)
+        return super(forms.HStoreField, self).has_changed(initial_value, data)
diff --git a/docs/releases/1.8.3.txt b/docs/releases/1.8.3.txt
index d5bde6040c..1155ac1cb6 100644
--- a/docs/releases/1.8.3.txt
+++ b/docs/releases/1.8.3.txt
@@ -15,5 +15,7 @@ Bugfixes
 * Fixed crash during :djadmin:`makemigrations` if a migrations module either
   is missing ``__init__.py`` or is a file (:ticket:`24848`).
 
-* Fixed ``exists()`` returning incorrect results after annotation with
+* Fixed ``QuerySet.exists()`` returning incorrect results after annotation with
   ``Count()`` (:ticket:`24835`).
+
+* Corrected ``HStoreField.has_changed()`` (:ticket:`24844`).
diff --git a/tests/postgres_tests/test_hstore.py b/tests/postgres_tests/test_hstore.py
index 8b2cc883dc..b36333d90c 100644
--- a/tests/postgres_tests/test_hstore.py
+++ b/tests/postgres_tests/test_hstore.py
@@ -4,6 +4,7 @@ from django.contrib.postgres import forms
 from django.contrib.postgres.fields import HStoreField
 from django.contrib.postgres.validators import KeysValidator
 from django.core import exceptions, serializers
+from django.forms import Form
 from django.test import TestCase
 
 from .models import HStoreModel
@@ -174,6 +175,12 @@ class TestFormField(TestCase):
         form_field = model_field.formfield()
         self.assertIsInstance(form_field, forms.HStoreField)
 
+    def test_empty_field_has_not_changed(self):
+        class HStoreFormTest(Form):
+            f1 = HStoreField()
+        form_w_hstore = HStoreFormTest()
+        self.assertFalse(form_w_hstore.has_changed())
+
 
 class TestValidator(TestCase):