Needs to have a value for field "id" before this many-to-many relationship can be used / Django [duplicate]

If you create clothes in admin, the above error "<Clothes: None: 0>" needs to have a value for field "id" before this many-to-many relationship can be used..

We also found that this error occurs on the save of the Clothes model.

This problem seems to be that the pk value is not assigned, so I tried using primary_key=True, but it doesn't seem to be the case. I have one more question. The likes of the Post model are also the same code as the save of the Clothes model, but the Post model is created without any problems. For what reason?

Below is the code of model.py

from django.db import models
# from django.contrib.auth.models import User
from django.conf import settings 
# from server.apps.user.models import Profile
  
class Clothes(models.Model):
  CATEGORYS =[
    (0, '상의'), #상의
    (1, '하의'), #하의
    (2, '아우터'), #아우터
    (3, '신발'), #신발
    (4, '악세사리'), #악세사리
  ]
  category = models.IntegerField(default=0,choices=CATEGORYS)
  img = models.ImageField(upload_to='main/images/clothes/%Y/%m/%d')
  save = models.ManyToManyField(settings.AUTH_USER_MODEL, related_name='Save', blank=True)
  author = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
  buying = models.TextField(null=True, blank=True)
  
  def __str__(self):
    return f'{self.pk}: {self.category}'
    #pk가 존재하지 않는것 같음. 

# class SavePeople(models.Model):
  

class Post(models.Model):
  main_img = models.ImageField(upload_to='main/images/post/%Y/%m/%d')
  title = models.CharField(max_length=100)
  content = models.TextField()
  private = models.BooleanField(default=False)
  author = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
  clothes = models.ManyToManyField(Clothes,related_name='Clothes')
  likes = models.ManyToManyField(settings.AUTH_USER_MODEL, related_name='Likes', blank=True)
  
  def __str__(self):
    return f'{self.pk}: {self.title}'
  
  def get_absolute_url(self):
    return f'/community/'
  #이거 나중에 detail page로 바꿔주세요
  
class Comment(models.Model):
  post = models.ForeignKey(Post, on_delete=models.CASCADE)
  author = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
  content = models.TextField()
  create_date = models.DateTimeField(auto_now_add=True)
  update_date = models.DateTimeField(auto_now_add=True)
  
  def __str__(self):
    return f'({self.author}) {self.post.title} :  {self.content}'
  
class Commu(models.Model):
  COMMU_CHOICES = [
    ('buying', 'buying'), #공동구매
    ('openrun', 'openrun'), #오픈런
    ('question', 'question'), #고민방
  ]
  category = models.CharField(max_length=20, choices=COMMU_CHOICES)
  img = models.ImageField(upload_to='main/images/commu/%Y/%m/%d', null=True, blank=True)
  title = models.CharField(max_length=100)
  content = models.TextField()
  author = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
  
  def __str__(self):
    return f'{self.pk}: {self.title}'
  
  def get_absolute_url(self):
    return f'/community/commu'

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