fix

submission/models.py

@@ -7,7 +7,12 @@ from task.models import Task
 
 
 class Submission(TimeStampedModel):
-    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    id = models.UUIDField(
+        primary_key=True,
+        default=uuid.uuid4,
+        editable=False,
+        unique=True,
+    )
     user = models.ForeignKey(
         User,
         on_delete=models.CASCADE,