diff --git a/polls/models.py b/polls/models.py
index 2b555b9..aaef6bb 100644
--- a/polls/models.py
+++ b/polls/models.py
@@ -54,7 +54,7 @@ class Notice(models.Model):
 
 class Task(models.Model):
     id = models.UUIDField('id', primary_key=True, default=uuid.uuid4)
-    created_by = models.ForeignKey(User, on_delete=models.SET_NULL)
+    created_by = models.ForeignKey(User, on_delete=models.CASCADE)
     groups = models.ManyToManyField(Group)
     content = models.TextField('内容', null=True, blank=True)
     added = models.DateTimeField(auto_now_add=True)
@@ -110,7 +110,6 @@ class Message(models.Model):
     send_to = models.ForeignKey(Group, on_delete=models.CASCADE)
     content = models.TextField('内容', null=True, blank=True)
     task = models.ForeignKey(Task, on_delete=models.CASCADE)
-    addition = models.ForeignKey(MessageAddition, on_delete=models.CASCADE)
 
     added = models.DateTimeField(auto_now_add=True)
     updated = models.DateTimeField(auto_now=True)
@@ -119,7 +118,7 @@ class Message(models.Model):
         ordering = ["-added"]
 
     def __str__(self):
-        return self.send_from + ':' + self.send_to
+        return self.send_from + ':' + self.send_toÒ
 
 
 class MessageAddition(models.Model):
diff --git a/polls/views/__pycache__/__init__.cpython-38.pyc b/polls/views/__pycache__/__init__.cpython-38.pyc
index 1e6d763..983abf0 100644
Binary files a/polls/views/__pycache__/__init__.cpython-38.pyc and b/polls/views/__pycache__/__init__.cpython-38.pyc differ
diff --git a/polls/views/__pycache__/user.cpython-38.pyc b/polls/views/__pycache__/user.cpython-38.pyc
index dddc807..149bf70 100644
Binary files a/polls/views/__pycache__/user.cpython-38.pyc and b/polls/views/__pycache__/user.cpython-38.pyc differ
diff --git a/requirements.txt b/requirements.txt
index b48e474..b8f8fb7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,4 +7,5 @@ aliyun-python-sdk-core-v3
 channels
 requests
 parsel
-django-summernote
\ No newline at end of file
+django-summernote
+python-dateutil
\ No newline at end of file