add message

announcement/models.py

@@ -1,6 +1,7 @@
 from django.db import models
 
 from account.models import User
+from submission.models import Submission
 from utils.models import RichTextField
 
 
@@ -18,3 +19,15 @@ class Announcement(models.Model):
     class Meta:
         db_table = "announcement"
         ordering = ("-top", "-create_time",)
+
+
+class Message(models.Model):
+    sender = models.ForeignKey(User, on_delete=models.CASCADE, related_name="sender")
+    recipient = models.ForeignKey(User, on_delete=models.CASCADE, related_name="recipient")
+    submission = models.ForeignKey(Submission, on_delete=models.CASCADE)
+    message = RichTextField()
+    create_time = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "message"
+        ordering = ("-create_time",)