old_contents: from django.db import models
  
  # Create your models here.
  
  class Event(models.Model):
      user_id = models.CharField(max_length=22)
      time = models.DateTimeField(auto_now_add=True)
  
  class PlannedCourse(Event):
      course_code = models.CharField(max_length=30)
      
  class FriendRequest(Event):
      new_friend = models.CharField(max_length=22)
  
  class NewFriendEvent(Event):
      new_friend = models.CharField(max_length=22)
  '''
  #this action can be "'became a friend of'" for friend adding or
  'enrolled to' for planing course. object should be friend_id or course_code
  '''
  class EventsLog(Event):
      action = models.CharField(max_length=40)
      object = models.CharField(max_length=30)
  
new_contents: from django.db import models
  
  # Create your models here.
  
  class Event(models.Model):
      user_id = models.CharField(max_length=22)
      time = models.DateTimeField(auto_now_add=True)
  
  class PlannedCourse(Event):
      course_code = models.CharField(max_length=30)
      
  class FriendRequest(Event):
      new_friend = models.CharField(max_length=22)
  
  class NewFriendEvent(Event):
      new_friend = models.CharField(max_length=22)
  '''
  #this action can be "'became a friend of'" for friend adding or
  'enrolled to' for planing course. object should be friend_id or department_code#course_code
  '''
  class EventsLog(Event):
      action = models.CharField(max_length=40)
      object = models.CharField(max_length=30)
  
subject: fix a bug