change queryset to prevent duplicates

zapisy/apps/theses/models.py

@@ -45,11 +45,12 @@ class ThesesQuerySet(models.QuerySet):
     def visible(self, user):
         if user.is_staff or is_theses_board_member(user):
             return self
+        student_theses = self.filter(students__user=user)
         return self.filter(
             (~Q(status=ThesisStatus.BEING_EVALUATED) & ~Q(status=ThesisStatus.RETURNED_FOR_CORRECTIONS)) |
             Q(advisor__user=user) |
             Q(supporting_advisor__user=user) |
-            Q(students__user=user)).distinct()
+            Q(id__in=student_theses))
 
 
 class Thesis(models.Model):