How to solve TypeError: on_delete must be callable on Django models?

Question

我突然收到一条错误消息 TypeError: on_delete must be callable. 我不知道如何解决此错误，因为我在代码中的任何地方都没有看到 field=models.ForeignKey(default=1, on_delete='CASCADE', to='main.Category'),。

  File "/home/arch/myproject/main/migrations/0014_auto_20191025_1154.py", line 6, in <module>
    class Migration(migrations.Migration):
  File "/home/arch/myproject/main/migrations/0014_auto_20191025_1154.py", line 47, in Migration
    field=models.ForeignKey(default=1, on_delete='CASCADE', to='main.Category'),
  File "/home/arch/.local/lib/python3.8/site-packages/django/db/models/fields/related.py", line 801, in __init__
    raise TypeError('on_delete must be callable.')

类型错误：on_delete 必须是可调用的。

Answer 1

根据 django docs，on_delete 参数必须是可调用的，而不是字符串。

这是 django.db.models 中定义的 CASCADE 可调用函数：

def CASCADE(collector, field, sub_objs, using):
    collector.collect(sub_objs, source=field.remote_field.model,
                      source_attr=field.name, nullable=field.null)
    if field.null and not connections[using].features.can_defer_constraint_checks:
        collector.add_field_update(field, None, sub_objs)

Answer 2

您的一个模型中的字段具有：

class SomeModel(models.Model):
    # …
    field=models.ForeignKey(default=1, <b><s>on_delete='CASCADE'</s></b>, to='main.Category')

但是你不能给on_delete=…参数传递一个字符串，它应该是：

class SomeModel(models.Model):
    # …
    field=models.ForeignKey(default=1, <b>on_delete=models.CASCADE</b>, to='main.Category')

您还需要删除迁移文件 (main/migrations/0014_auto_20191025_1154.py)，然后进行新的迁移。

How to solve TypeError: on_delete must be callable on Django models?

How to solve TypeError: on_delete must be callable on Django models?

python

django

django-models

cascade