Optimize Problem.name to support prefetching

oioioi/problems/models.py

@@ -119,10 +119,17 @@ class Problem(models.Model):
 
     @cached_property
     def name(self):
-        problem_name = ProblemName.objects.filter(
-            problem=self, language=get_language()
-        ).first()
-        return problem_name.name if problem_name else self.legacy_name
+        # We fetch all of self.names and filter by language in Python instead of Django. 
+        # This allows us to do prefetch_related('names'), which considerably speeds up 
+        # views such as task_archive_tag_view that query many problems and their associated names
+
+        # Check if primary key exists, as it's needed to access related fields such as `names`
+        if self.pk:
+            for problem_name in self.names.all():
+                if problem_name.language == get_language():
+                    return problem_name.name
+
+        return self.legacy_name
 
     @property
     def controller(self):
@@ -1046,4 +1053,4 @@ def decrease_aggregated_algorithm_tag_proposal(sender, instance, **kwargs):
 
 @receiver(post_delete, sender=DifficultyTagProposal)
 def decrease_aggregated_difficulty_tag_proposal(sender, instance, **kwargs):
-    decrease_aggregated_tag_proposal(sender, instance, AggregatedDifficultyTagProposal, **kwargs)
+    decrease_aggregated_tag_proposal(sender, instance, AggregatedDifficultyTagProposal, **kwargs)

oioioi/problems/tests/test_problem.py

@@ -4,6 +4,7 @@
 
 import six
 import urllib.parse
+from django.conf import settings
 from django.contrib.auth.models import AnonymousUser, Permission, User
 from django.contrib.contenttypes.models import ContentType
 from django.core.files.base import ContentFile
@@ -21,6 +22,7 @@
     DifficultyTag,
     DifficultyTagThrough,
     Problem,
+    ProblemName,
     ProblemAttachment,
     ProblemPackage,
     ProblemStatement,
@@ -867,3 +869,18 @@ def test_search_tags_basic(self):
         )
         self.assertEqual(response.status_code, 200)
         self.assert_contains_only(response, ())
+
+def problem_name(problem, language):
+    problem_name = ProblemName.objects.filter(
+        problem=problem, language=language
+    ).first()
+    return problem_name.name if problem_name else problem.legacy_name
+
+class TestProblemName(TestCase):
+    fixtures = ['test_problem_search']
+
+    def test_problem_names(self):
+        for (lang_code, _) in settings.LANGUAGES:
+            with override_settings(LANGUAGE_CODE=lang_code):
+                for problem in Problem.objects.all():
+                    self.assertEqual(problem.name, problem_name(problem, lang_code))

oioioi/problems/views.py

@@ -895,7 +895,9 @@ def task_archive_tag_view(request, origin_tag):
         origin_tag.problems.all()
         .select_related('problemsite', 'main_problem_instance')
         .prefetch_related(
-            'origininfovalue_set__localizations', 'origininfovalue_set__category'
+            'origininfovalue_set__localizations', 
+            'origininfovalue_set__category',
+            'names'
         )
     )
     problems = _filter_problems_prefetched(problems, request.GET)