Refactor prefetching into a method on the queryset

Author: davidfischer

readthedocs/core/templatetags/privacy_tags.py

@@ -20,21 +20,11 @@ def is_admin(user, project):
 
 @register.simple_tag(takes_context=True)
 def get_public_projects(context, user):
-    # Creates a Subquery object which returns the latest builds 'id'.
-    # Used for optimization purpose.
-    subquery = Subquery(
-        Build.objects.filter(
-            project=OuterRef('project_id')).values_list('id', flat=True)[:1]
-    )
-    # Filters the latest builds of projects.
-    latest_build = Prefetch('builds', Build.objects.filter(
-        pk__in=subquery), to_attr=Project.LATEST_BUILD_CACHE
-    )
     # 'Exists()' checks if the project has any good builds.
     projects = Project.objects.for_user_and_viewer(
         user=user,
         viewer=context['request'].user,
-    ).prefetch_related('users', latest_build).annotate(
+    ).prefetch_latest_build().annotate(
         _good_build=Exists(
             Build.objects.filter(success=True, project=OuterRef('pk')))
     )

readthedocs/projects/querysets.py

@@ -75,14 +75,14 @@ def is_active(self, project):
 
         return True
 
-    # Aliases
+    def prefetch_latest_build(self):
+        """
+        For a given queryset of projects, prefetch the latest build for each project
 
-    def dashboard(self, user=None):
-        """Get the projects for this user including the latest build"""
+        This should come after any filtering.
+        """
         from readthedocs.builds.models import Build
 
-        projects = self.for_admin_user(user)
-
         # Prefetch the latest build for each project.
         subquery = Subquery(
             Build.objects.filter(project=OuterRef('project_id')).values_list('id', flat=True)[:1]
@@ -92,8 +92,13 @@ def dashboard(self, user=None):
             Build.objects.filter(pk__in=subquery),
             to_attr=self.model.LATEST_BUILD_CACHE,
         )
+        return self.prefetch_related(latest_build)
+
+    # Aliases
 
-        return projects.prefetch_related(latest_build)
+    def dashboard(self, user=None):
+        """Get the projects for this user including the latest build"""
+        return self.for_admin_user(user).prefetch_latest_build()
 
     def api(self, user=None, detail=True):
         if detail: