Add raw SQL fallback for 'last edited pages' query for MySQL

wagtail/wagtailadmin/views/home.py

@@ -2,6 +2,7 @@ from __future__ import absolute_import, unicode_literals
 
 from django.conf import settings
 from django.contrib.auth import get_user_model
+from django.db import connection
 from django.db.models import Max
 from django.shortcuts import render
 from django.template.loader import render_to_string
@@ -56,10 +57,27 @@ class RecentEditsPanel(object):
 
         # Last n edited pages
         edit_count = getattr(settings, 'WAGTAILADMIN_RECENT_EDITS_LIMIT', 5)
+        if connection.vendor == 'mysql':
+            # MySQL can't handle the subselect created by the ORM version -
+            # it fails with "This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'"
+            last_edits = PageRevision.objects.raw(
+                """
+                SELECT wp.* FROM
+                    wagtailcore_pagerevision wp JOIN (
+                        SELECT max(created_at) AS max_created_at, page_id FROM
+                            wagtailcore_pagerevision WHERE user_id = %s GROUP BY page_id ORDER BY max_created_at DESC LIMIT %s
+                    ) AS max_rev ON max_rev.max_created_at = wp.created_at ORDER BY wp.created_at DESC
+                 """, [
+                    User._meta.pk.get_db_prep_value(self.request.user.pk, connection),
+                    edit_count
+                ]
+            )
+        else:
             last_edits_dates = (PageRevision.objects.filter(user=self.request.user)
                                 .values('page_id').annotate(latest_date=Max('created_at'))
                                 .order_by('-latest_date').values('latest_date')[:edit_count])
             last_edits = PageRevision.objects.filter(created_at__in=last_edits_dates).order_by('-created_at')
+
         page_keys = [pr.page_id for pr in last_edits]
         pages = Page.objects.specific().in_bulk(page_keys)
         self.last_edits = [