尝试创建 Django 迁移时，ForeignKey 缺少必需的位置参数 on_delete

Posted 2023-02-24

【中文标题】尝试创建 Django 迁移时，ForeignKey 缺少必需的位置参数 on_delete

【英文标题】：ForeignKey missing required positional argument on_delete when trying to create a Django migration

【发布时间】：2018-11-09 00:41:01

【问题描述】：

我正在尝试使用 python/django 和 postgres 创建表。我为models.py 中的每个数据库表创建类。当我尝试创建迁移时，它给了我这个错误：

File "..\database\models.py", line 40, in <module>
    class group(models.Model):
File "database\models.py", line 41, in group
    user_id = models.ForeignKey(user) TypeError: __init__() missing 1 required positional argument: 'on_delete'

这是我的代码

class user(models.Model):
    STATUS_CHOICES = (
        ('active','Active'),
        ('not active', 'Not active')
    )
    user_id= models.AutoField(primary_key=True)
    first_name = models.CharField(max_length=50)
    last_name = models.CharField(max_length=50)
    email = models.EmailField(max_length=70, null=True, blank=True, unique=True)
    phone = models.CharField( max_length=17, blank=True)
    gender = models.CharField(max_length=50)
    region = models.CharField(max_length=50)
    password = models.CharField(widget=models.PasswordInput)
    active = models.CharField(max_length=50, choices=STATUS_CHOICES, default='not active')
    register_date = models.DateField(default=date.today)

    def _str_(self):
        return self.user_id

class train(models.Model):
    train_CHOICES = (
        ('intercity', 'Intercity'),
        ('sprinter', 'Sprinter')
    )
    train_id= models.AutoField(primary_key=True)
    train_type = models.CharField(max_length=50, choices=train_CHOICES, default='intercity')

    def _str_(self):
        return self.train_id

class group(models.Model):
    user_id = models.ForeignKey(user)
    group_id = models.AutoField(primary_key=True)
    trip_id = models.ForeignKey(trip)
    created_date = models.DateField(default=date.today)
    started_at = models.DateTimeField()

    def _str_(self):
        return self.group_id

我对 Python 真的很陌生。我认为有很多错误。能给个提示吗？

【参考方案1】：

由于 Django 2.0，on_delete 是 ForeignKey 的必需参数（在旧版本中默认为 CASCADE），您应该为所有 ForeignKey 字段添加它：

user_id = models.ForeignKey(user, on_delete=models.CASCADE)
trip_id = models.ForeignKey(trip, on_delete=models.CASCADE)

注意on_delete=models.CASCADE 表示在删除用户或行程对象时，Django 会删除包含 ForeignKey 的对象。您可以找到其他选项列表here。