Fixed #14850 -- Cleaned up duplicate code in admin formset handling.

Thanks apollo13 for the report and review.

django/contrib/admin/options.py

@@ -1107,17 +1107,7 @@ class ModelAdmin(BaseModelAdmin):
             else:
                 form_validated = False
                 new_object = self.model()
-            prefixes = {}
+            formsets = self._create_formsets(request, new_object, inline_instances)
-            for FormSet, inline in zip(self.get_formsets(request), inline_instances):
-                prefix = FormSet.get_default_prefix()
-                prefixes[prefix] = prefixes.get(prefix, 0) + 1
-                if prefixes[prefix] != 1 or not prefix:
-                    prefix = "%s-%s" % (prefix, prefixes[prefix])
-                formset = FormSet(data=request.POST, files=request.FILES,
-                                  instance=new_object,
-                                  save_as_new="_saveasnew" in request.POST,
-                                  prefix=prefix, queryset=inline.get_queryset(request))
-                formsets.append(formset)
             if all_valid(formsets) and form_validated:
                 self.save_model(request, new_object, form, False)
                 self.save_related(request, form, formsets, False)
@@ -1135,15 +1125,7 @@ class ModelAdmin(BaseModelAdmin):
                 if isinstance(f, models.ManyToManyField):
                     initial[k] = initial[k].split(",")
             form = ModelForm(initial=initial)
-            prefixes = {}
+            formsets = self._create_formsets(request, self.model(), inline_instances)
-            for FormSet, inline in zip(self.get_formsets(request), inline_instances):
-                prefix = FormSet.get_default_prefix()
-                prefixes[prefix] = prefixes.get(prefix, 0) + 1
-                if prefixes[prefix] != 1 or not prefix:
-                    prefix = "%s-%s" % (prefix, prefixes[prefix])
-                formset = FormSet(instance=self.model(), prefix=prefix,
-                                  queryset=inline.get_queryset(request))
-                formsets.append(formset)
 
         adminForm = helpers.AdminForm(form, list(self.get_fieldsets(request)),
             self.get_prepopulated_fields(request),
@@ -1195,7 +1177,6 @@ class ModelAdmin(BaseModelAdmin):
                                     current_app=self.admin_site.name))
 
         ModelForm = self.get_form(request, obj)
-        formsets = []
         inline_instances = self.get_inline_instances(request, obj)
         if request.method == 'POST':
             form = ModelForm(request.POST, request.FILES, instance=obj)
@@ -1205,18 +1186,7 @@ class ModelAdmin(BaseModelAdmin):
             else:
                 form_validated = False
                 new_object = obj
-            prefixes = {}
+            formsets = self._create_formsets(request, new_object, inline_instances)
-            for FormSet, inline in zip(self.get_formsets(request, new_object), inline_instances):
-                prefix = FormSet.get_default_prefix()
-                prefixes[prefix] = prefixes.get(prefix, 0) + 1
-                if prefixes[prefix] != 1 or not prefix:
-                    prefix = "%s-%s" % (prefix, prefixes[prefix])
-                formset = FormSet(request.POST, request.FILES,
-                                  instance=new_object, prefix=prefix,
-                                  queryset=inline.get_queryset(request))
-
-                formsets.append(formset)
-
             if all_valid(formsets) and form_validated:
                 self.save_model(request, new_object, form, True)
                 self.save_related(request, form, formsets, True)
@@ -1226,15 +1196,7 @@ class ModelAdmin(BaseModelAdmin):
 
         else:
             form = ModelForm(instance=obj)
-            prefixes = {}
+            formsets = self._create_formsets(request, obj, inline_instances)
-            for FormSet, inline in zip(self.get_formsets(request, obj), inline_instances):
-                prefix = FormSet.get_default_prefix()
-                prefixes[prefix] = prefixes.get(prefix, 0) + 1
-                if prefixes[prefix] != 1 or not prefix:
-                    prefix = "%s-%s" % (prefix, prefixes[prefix])
-                formset = FormSet(instance=obj, prefix=prefix,
-                                  queryset=inline.get_queryset(request))
-                formsets.append(formset)
 
         adminForm = helpers.AdminForm(form, self.get_fieldsets(request, obj),
             self.get_prepopulated_fields(request, obj),
@@ -1533,6 +1495,32 @@ class ModelAdmin(BaseModelAdmin):
             "admin/object_history.html"
         ], context, current_app=self.admin_site.name)
 
+    def _create_formsets(self, request, obj, inline_instances):
+        "Helper function to generate formsets for add/change_view."
+        formsets = []
+        prefixes = {}
+        get_formsets_args = [request]
+        if obj.pk:
+            get_formsets_args.append(obj)
+        for FormSet, inline in zip(self.get_formsets(*get_formsets_args), inline_instances):
+            prefix = FormSet.get_default_prefix()
+            prefixes[prefix] = prefixes.get(prefix, 0) + 1
+            if prefixes[prefix] != 1 or not prefix:
+                prefix = "%s-%s" % (prefix, prefixes[prefix])
+            formset_params = {
+                'instance': obj,
+                'prefix': prefix,
+                'queryset': inline.get_queryset(request),
+            }
+            if request.method == 'POST':
+                formset_params.update({
+                    'data': request.POST,
+                    'files': request.FILES,
+                    'save_as_new': '_saveasnew' in request.POST
+                })
+            formsets.append(FormSet(**formset_params))
+        return formsets
+
 
 class InlineModelAdmin(BaseModelAdmin):
     """