Reduce overhead of fetching all data from database

In case we need just one value, fetch only it.
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/accounts/models.py

@@ -571,7 +571,9 @@ class Profile(models.Model):
         Returns date of last change user has done in Weblate.
         '''
         try:
-            return self.user.change_set.all()[0].timestamp
+            return self.user.change_set.values_list(
+                'timestamp', flat=True
+                )[0]
         except IndexError:
             return None
 

weblate/sitemaps.py

@@ -36,7 +36,7 @@ class PagesSitemap(Sitemap):
         return item[0]
 
     def lastmod(self, item):
-        return Change.objects.all()[0].timestamp
+        return Change.objects.values_list('timestamp', flat=True)[0]
 
     def priority(self, item):
         return item[1]

weblate/trans/models/project.py

@@ -317,7 +317,11 @@ class Project(models.Model, PercentMixin, URLMixin, PathMixin):
         totals = []
         for component in self.subproject_set.all():
             try:
-                totals.append(component.translation_set.all()[0].total)
+                totals.append(
+                    component.translation_set.values_list(
+                        'total', flat=True
+                    )[0]
+                )
             except IndexError:
                 pass
         return sum(totals)
@@ -331,7 +335,11 @@ class Project(models.Model, PercentMixin, URLMixin, PathMixin):
         totals = []
         for component in self.subproject_set.all():
             try:
-                totals.append(component.translation_set.all()[0].total_words)
+                totals.append(
+                    component.translation_set.values_list(
+                        'total_words', flat=True
+                    )[0]
+                )
             except IndexError:
                 pass
         return sum(totals)

weblate/trans/models/subproject.py

@@ -1392,10 +1392,11 @@ class SubProject(models.Model, PercentMixin, URLMixin, PathMixin):
     def last_change(self):
         """Returns date of last change done in Weblate."""
         try:
-            change = Change.objects.content().filter(
+            return Change.objects.content().filter(
                 translation__subproject=self
-            )
-            return change[0].timestamp
+            ).values_list(
+                'timestamp', flat=True
+            )[0]
         except IndexError:
             return None
 

weblate/trans/models/unit.py

@@ -243,7 +243,9 @@ class UnitManager(models.Manager):
 
             return base.filter(query)
         else:
-            lang = self.all()[0].translation.language.code
+            lang = self.values_list(
+                'translation__language__code', flat=True
+            )[0]
             return base.filter(
                 pk__in=fulltext_search(
                     params['q'],

weblate/trans/views/checks.py

@@ -182,12 +182,14 @@ def show_check_project(request, name, project):
         )
         for subproject in prj.subproject_set.all():
             try:
-                lang = subproject.translation_set.all()[0].language
+                lang_id = subproject.translation_set.values_list(
+                    'language_id', flat=True
+                )[0]
             except IndexError:
                 continue
             res = Unit.objects.filter(
                 contentsum__in=checks,
-                translation__language=lang,
+                translation__language_id=lang_id,
                 translation__subproject=subproject
             ).values(
                 'translation__subproject__slug',