update to django 2.0

problem/models.py

@@ -28,7 +28,7 @@ class ProblemDifficulty(object):
 class Problem(models.Model):
     # display ID
     _id = models.TextField(db_index=True)
-    contest = models.ForeignKey(Contest, null=True)
+    contest = models.ForeignKey(Contest, null=True, on_delete=models.CASCADE)
     # for contest problem
     is_public = models.BooleanField(default=False)
     title = models.TextField()
@@ -47,7 +47,7 @@ class Problem(models.Model):
     create_time = models.DateTimeField(auto_now_add=True)
     # we can not use auto_now here
     last_update_time = models.DateTimeField(null=True)
-    created_by = models.ForeignKey(User)
+    created_by = models.ForeignKey(User, on_delete=models.CASCADE)
     # ms
     time_limit = models.IntegerField()
     # MB

problem/views/oj.py

@@ -25,7 +25,7 @@ class PickOneAPI(APIView):
 class ProblemAPI(APIView):
     @staticmethod
     def _add_problem_status(request, queryset_values):
-        if request.user.is_authenticated():
+        if request.user.is_authenticated:
             profile = request.user.userprofile
             acm_problems_status = profile.acm_problems_status.get("problems", {})
             oi_problems_status = profile.oi_problems_status.get("problems", {})
@@ -81,7 +81,7 @@ class ProblemAPI(APIView):
 
 class ContestProblemAPI(APIView):
     def _add_problem_status(self, request, queryset_values):
-        if request.user.is_authenticated():
+        if request.user.is_authenticated:
             profile = request.user.userprofile
             if self.contest.rule_type == ContestRuleType.ACM:
                 problems_status = profile.acm_problems_status.get("contest_problems", {})