Django Charfield null = False不引发完整性错误 [英] Django Charfield null=False Integrity Error not raised

问题描述

我有一个模型：

class Discount(models.Model):
    code = models.CharField(max_length=14, unique=True, null=False, blank=False)
    email = models.EmailField(unique=True)
    discount = models.IntegerField(default=10)

在我的shell中，当我尝试保存没有输入的Discount对象时，它不会引发错误。我在做什么错了？

In my shell when I try and save a Discount object with no input, it doesn't raise an error. What am I doing wrong?

> e = Discount()
> e.save()

推荐答案

没有默认的Django行为会保存 CHAR 或 TEXT 类型为 Null -它将始终使用一个空字符串（''）。 null = False 对这些类型的字段没有影响。

No default Django behavior will save CHAR or TEXT types as Null - it will always use an empty string (''). null=False has no effect on these types of fields.

blank = False 表示在使用模型渲染ModelForm时，默认情况下该字段是必需的。它不会阻止您手动保存不带该值的模型实例。

blank=False means that the field will be required by default when the model is used to render a ModelForm. It does not prevent you from manually saving a model instance without that value.

这里想要的是自定义模型验证器：

What you want here is a custom model validator:

from django.core.exceptions import ValidationError
def validate_not_empty(value):
    if value == '':
        raise ValidationError('%(value)s is empty!'), params={'value':value})

然后将验证器添加到模型中：

Then add the validator to your model:

code = models.CharField(max_length=14, unique=True, validators=[validate_not_empty])

这将处理您想要的表单验证，但是验证器不会自动运行保存模型实例时。 在此处进一步阅读。每次保存实例时都要对此进行验证，我建议重写默认的 save 行为，在其中检查字符串的值，并在必要时通过引发错误来中断保存。 在此处覆盖保存的好帖子。

This will take care of the form validation you want, but validators don't automatically run when a model instance is saved. Further reading here. If you want to validate this every time an instance is saved, I suggest overriding the default save behavior, checking the value of your string there, and interrupting the save by raising an error if necessary. Good post on overriding save here.

更多读取 null ：

避免在基于字符串的字符串上使用null字段（例如CharField和TextField），因为空字符串值将始终存储为空字符串，而不是NULL。如果基于字符串的字段具有null = True，则意味着它具有无数据的两个可能值：NULL和空字符串。在大多数情况下，为无数据设置两个可能的值是多余的； Django惯例是使用空字符串，而不是NULL。

Avoid using null on string-based fields such as CharField and TextField because empty string values will always be stored as empty strings, not as NULL. If a string-based field has null=True, that means it has two possible values for "no data": NULL, and the empty string. In most cases, it’s redundant to have two possible values for "no data;" the Django convention is to use the empty string, not NULL.

并在验证器上。

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