Wrap deleting page into database transaction

Currently queries executed in the hooks don't run in the transaction
with the page deletion query and it's harder to write hook without
copying the whole view if you want to keep queries running in the hooks
integral with page deletion.

CHANGELOG.txt

@@ -10,6 +10,7 @@ Changelog
  * EmbedBlock now validates against recognised embed providers on save (Bertrand Bordage)
  * Fix: Respect next param on login (Loic Teixeira)
  * Fix: InlinePanel now handles relations that specify a related_query_name (Aram Dulyan)
+ * Fix: before_delete_page / after_delete_page hooks now run within the same database transaction as the page deletion (Tomasz Knapik)
 
 
 2.2.1 (13.08.2018)

docs/releases/2.3.rst

@@ -32,6 +32,7 @@ Bug fixes
 
  * Respect next param on login (Loic Teixeira)
  * InlinePanel now handles relations that specify a related_query_name (Aram Dulyan)
+ * before_delete_page / after_delete_page hooks now run within the same database transaction as the page deletion (Tomasz Knapik)
 
 
 Upgrade considerations

wagtail/admin/views/pages.py

@@ -2,6 +2,7 @@ from time import time
 
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import PermissionDenied
+from django.db import transaction
 from django.db.models import Count
 from django.http import Http404, HttpResponse, JsonResponse
 from django.http.request import QueryDict
@@ -541,27 +542,28 @@ def delete(request, page_id):
     if not page.permissions_for_user(request.user).can_delete():
         raise PermissionDenied
 
-    for fn in hooks.get_hooks('before_delete_page'):
-        result = fn(request, page)
-        if hasattr(result, 'status_code'):
-            return result
-
-    next_url = get_valid_next_url_from_request(request)
-
-    if request.method == 'POST':
-        parent_id = page.get_parent().id
-        page.delete()
-
-        messages.success(request, _("Page '{0}' deleted.").format(page.get_admin_display_title()))
-
-        for fn in hooks.get_hooks('after_delete_page'):
+    with transaction.atomic():
+        for fn in hooks.get_hooks('before_delete_page'):
             result = fn(request, page)
             if hasattr(result, 'status_code'):
                 return result
 
-        if next_url:
-            return redirect(next_url)
-        return redirect('wagtailadmin_explore', parent_id)
+        next_url = get_valid_next_url_from_request(request)
+
+        if request.method == 'POST':
+            parent_id = page.get_parent().id
+            page.delete()
+
+            messages.success(request, _("Page '{0}' deleted.").format(page.get_admin_display_title()))
+
+            for fn in hooks.get_hooks('after_delete_page'):
+                result = fn(request, page)
+                if hasattr(result, 'status_code'):
+                    return result
+
+            if next_url:
+                return redirect(next_url)
+            return redirect('wagtailadmin_explore', parent_id)
 
     return render(request, 'wagtailadmin/pages/confirm_delete.html', {
         'page': page,