Optimize the db query on group edit page.

A couple of related selects and prefetches on the content types
and permissions will cut down the query count slightly.

wagtail/wagtailadmin/forms.py

@@ -404,8 +404,8 @@ class BaseGroupCollectionMemberPermissionFormSet(forms.BaseFormSet):
 
         for collection, collection_permissions in groupby(
             instance.collection_permissions.filter(
-                permission__in=self.permission_queryset,
-            ).order_by('collection'),
+                permission__in=self.permission_queryset
+            ).select_related('permission__content_type', 'collection').order_by('collection'),
             lambda cp: cp.collection
         ):
             initial_data.append({
@@ -500,7 +500,7 @@ def collection_member_permission_formset_factory(
     permission_queryset = Permission.objects.filter(
         content_type__app_label=model._meta.app_label,
         codename__in=[codename for codename, short_label, long_label in permission_types]
-    )
+    ).select_related('content_type')
 
     if default_prefix is None:
         default_prefix = '%s_permissions' % model._meta.model_name
@@ -512,7 +512,7 @@ def collection_member_permission_formset_factory(
         (i.e. group or user) for a specific collection
         """
         collection = forms.ModelChoiceField(
-            queryset=Collection.objects.all()
+            queryset=Collection.objects.all().prefetch_related('group_permissions')
         )
         permissions = forms.ModelMultipleChoiceField(
             queryset=permission_queryset,

wagtail/wagtailusers/forms.py

@@ -201,7 +201,7 @@ class GroupForm(forms.ModelForm):
         self.registered_permissions = Permission.objects.none()
         for fn in hooks.get_hooks('register_permissions'):
             self.registered_permissions = self.registered_permissions | fn()
-        self.fields['permissions'].queryset = self.registered_permissions
+        self.fields['permissions'].queryset = self.registered_permissions.select_related('content_type')
 
     required_css_class = "required"
 
@@ -276,7 +276,7 @@ class BaseGroupPagePermissionFormSet(forms.BaseFormSet):
         initial_data = []
 
         for page, page_permissions in groupby(
-            instance.page_permissions.order_by('page'), lambda pp: pp.page
+            instance.page_permissions.select_related('page').order_by('page'), lambda pp: pp.page
         ):
             initial_data.append({
                 'page': page,