Fixed #22135 -- Added ModelAdmin.get_changeform_initial_data().

Allows custom behavior for setting initial form data in ModelAdmin.
By default, initial data is set via GET params. The new method allows
this behavior to be overridden.

Thanks egasimus for the suggestion.

django/contrib/admin/options.py

@@ -1308,6 +1308,22 @@ class ModelAdmin(BaseModelAdmin):
             inline_admin_formsets.append(inline_admin_formset)
         return inline_admin_formsets
 
+    def get_changeform_initial_data(self, request):
+        """
+        Get the initial form data.
+        Unless overridden, this populates from the GET params.
+        """
+        initial = dict(request.GET.items())
+        for k in initial:
+            try:
+                f = self.model._meta.get_field(k)
+            except models.FieldDoesNotExist:
+                continue
+            # We have to special-case M2Ms as a list of comma-separated PKs.
+            if isinstance(f, models.ManyToManyField):
+                initial[k] = initial[k].split(",")
+        return initial
+
     @csrf_protect_m
     @transaction.atomic
     def changeform_view(self, request, object_id=None, form_url='', extra_context=None):
@@ -1358,16 +1374,7 @@ class ModelAdmin(BaseModelAdmin):
                     return self.response_change(request, new_object)
         else:
             if add:
-                # Prepare the dict of initial data from the request.
-                # We have to special-case M2Ms as a list of comma-separated PKs.
-                initial = dict(request.GET.items())
-                for k in initial:
-                    try:
-                        f = opts.get_field(k)
-                    except models.FieldDoesNotExist:
-                        continue
-                    if isinstance(f, models.ManyToManyField):
-                        initial[k] = initial[k].split(",")
+                initial = self.get_changeform_initial_data(request)
                 form = ModelForm(initial=initial)
                 formsets, inline_instances = self._create_formsets(request, self.model())
             else:

docs/ref/contrib/admin/index.txt

@@ -1709,6 +1709,21 @@ templates used by the :class:`ModelAdmin` views:
     ``obj_display`` is a string with the name of the deleted
     object.
 
+.. method:: ModelAdmin.get_changeform_initial_data(request)
+
+    .. versionadded:: 1.7
+
+    A hook for the initial data on admin change forms. By default, fields are
+    given initial values from ``GET`` parameters. For instance,
+    ``?name=initial_value`` will set the ``name`` field's initial value to be
+    ``initial_value``.
+
+    This method should return a dictionary in the form
+    ``{'fieldname': 'fieldval'}``::
+
+        def get_changeform_initial_data(self, request):
+            return {'name': 'custom_initial_value'}
+
 Other methods
 ~~~~~~~~~~~~~
 

docs/releases/1.7.txt

@@ -308,6 +308,10 @@ Minor features
   <django.contrib.admin.ModelAdmin.list_display>` value by prefixing the
   ``admin_order_field`` value with a hyphen.
 
+* The :meth:`ModelAdmin.get_changeform_initial_data()
+  <django.contrib.admin.ModelAdmin.get_changeform_initial_data>` method may be
+  overridden to define custom behavior for setting initial change form data.
+
 :mod:`django.contrib.auth`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 

tests/admin_views/admin.py

@@ -796,6 +796,10 @@ class RestaurantAdmin(admin.ModelAdmin):
     inlines = [WorkerInlineAdmin]
     view_on_site = False
 
+    def get_changeform_initial_data(self, request):
+        return {'name': 'overridden_value'}
+
+
 site = admin.AdminSite(name="admin")
 site.register(Article, ArticleAdmin)
 site.register(CustomArticle, CustomArticleAdmin)

tests/admin_views/tests.py

@@ -765,6 +765,19 @@ class AdminViewFormUrlTest(TestCase):
         self.assertTrue('form_url' in response.context, msg='form_url not present in response.context')
         self.assertEqual(response.context['form_url'], 'pony')
 
+    def testInitialDataCanBeOverridden(self):
+        """
+        Tests that the behavior for setting initial
+        form data can be overridden in the ModelAdmin class.
+
+        Usually, the initial value is set via the GET params.
+        """
+        response = self.client.get('/test_admin/%s/admin_views/restaurant/add/' % self.urlbit, {'name': 'test_value'})
+        # this would be the usual behaviour
+        self.assertNotContains(response, 'value="test_value"')
+        # this is the overridden behaviour
+        self.assertContains(response, 'value="overridden_value"')
+
 
 @override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',))
 class AdminJavaScriptTest(TestCase):