TypeError：int（）参数必须是字符串或数字，而不是“模型实例”

Here's my models.py:

这是我的models.py:

from django.db import models

class Location(models.Model):
   location_name = models.CharField(max_length=100)
   def __unicode__(self):
      return self.location_name

class Menu(models.Model):
   location = models.ManyToManyField(Location)
   restaurant_name = models.CharField(max_length=200)
   dish_category = models.CharField(max_length=100)
   dish_name = models.CharField(max_length=200)
   VNV_tag = models.CharField(max_length=100)
   quantity = models.CharField(max_length=10, default='FULL')
   price = models.CharField(max_length=5, default=0)
   def __unicode__(self):
       return self.restaurant_name
from dj