Question

如何正确编写模型默认函数？

我有一个TestDefalt模型及其默认功能：

def genefunc(instance, detail):

    str = instance.name + "/abc/"

    return str

class TestDefalt(models.Model):
    name = models.CharField(max_length=11)
    detail = models.CharField(default=genefunc, max_length=11)

在我的序列化器和视图中：

# serializer
class TestDefaultSerializer(ModelSerializer):
    class Meta:
        model = TestDefalt
        fields = "__all__"

# view
class TestDCreateAPIView(CreateAPIView):
    serializer_class = TestDefaultSerializer
    permission_classes = []
    queryset = TestDefalt.objects.all()

当我访问TestDCreateAPIView时，我得到了以下错误：

TypeError at /test04/
Got a `TypeError` when calling `TestDefalt.objects.create()`. This may be because you have a writable field on the serializer class that is not a valid argument to `TestDefalt.objects.create()`. You may need to make the field read-only, or override the TestDefaultSerializer.create() method to handle this correctly.
...

File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/db/models/fields/__init__.py", line 782, in get_default
    return self._get_default()
TypeError: genefunc() missing 2 required positional arguments: 'instance' and 'detail'

Answer 1

如果某个字段default的值是可调用的，则无需任何参数即可调用它，因此您的解决方案无法正常工作。这里适当的解决方案是覆盖save()方法：

class TestDefalt(models.Model):
    name = models.CharField(max_length=11)
    detail = models.CharField(default='', max_length=11)

    def save(self, *args, **kw):
        if not self.pk and not self.detail:
            self.detail = self.name + "whatever"
        return super(TestDefalt).save(*args, **kw)

请注意，如果len(self.name) == 11，len(self.name + "something")将是＆gt; 11，所以你可能想为maxlength设置更大的detail。

如何正确编写模型默认函数？

1 个答案: