在模型中null=True和blank=True的含义还取决于这些字段在表单类中的定义方式。

假设你已经定义了以下类:

class Client (models.Model):
    name = models.CharField (max_length=100, blank=True)
    address = models.CharField (max_length=100, blank=False)

如果表单类是这样定义的:

class ClientForm (ModelForm):
    class Meta:
        model = Client
        fields = ['name', 'address']
        widgets = {
            'name': forms.TextInput (attrs = {'class': 'form-control form-control-sm'}),
            'address': forms.TextInput (attrs = {'class': 'form-control form-control-sm'})
        }

然后，'name'字段将不是强制性的(由于模型中的空白=True)， 'address'字段将是强制性的(由于模型中的空白=False)。

然而，如果ClientForm类是这样定义的:

class ClientForm (ModelForm):
    class Meta:
        model = Client
        fields = ['name', 'address']

    name = forms.CharField (
        widget = forms.TextInput (attrs = {'class': 'form-control form-control-sm'}),
    )
    address = forms.CharField (
        widget = forms.TextInput (attrs = {'class': 'form-control form-control-sm'}),
    )

然后，这两个字段('name'和'address')将是强制性的，“因为声明式定义的字段保持原样”(https://docs.djangoproject.com/en/3.0/topics/forms/modelforms/)，即表单字段的'required'属性的默认值为True，这将要求字段'name'和'address'被填充，即使在模型中，字段已被设置为blank=True。

你可能有你的答案，但直到今天，很难判断是否把null=True或空白=True或两者都放在一个字段。我个人认为为开发者提供这么多选择是非常无用和令人困惑的。让它按自己的意愿处理空值或空格。

下面是来自Two Scoops of Django的表格:

当我们在Django管理中保存任何东西时，会发生两步验证，在Django级别和数据库级别。我们不能在数字字段中保存文本。

数据库的数据类型是NULL，什么都不是。当Django在数据库中创建列时，它指定它们不能为空。如果你试图保存NULL，你会得到数据库错误。

同样在Django- admin级别，默认情况下所有字段都是必须的，你不能保存空白字段，Django会给你一个错误。

所以，如果你想保存空白字段，你需要在Django和数据库级别上允许它。 blank=True -在管理面板中允许空字段 null=True -将允许将null保存到数据库列。

理解Django模型字段定义中的选项(至少)有两个目的是至关重要的:定义数据库表，定义模型表单的默认格式和验证。(我说“默认”是因为可以通过提供自定义表单来覆盖这些值。)一些选项会影响数据库，一些选项会影响表单，还有一些会同时影响两者。

说到null和blank，其他答案已经说明，前者影响数据库表定义，后者影响模型验证。我认为，通过查看所有四种可能配置的用例，可以更清楚地区分它们:

null=False, blank=False: This is the default configuration and means that the value is required in all circumstances. null=True, blank=True: This means that the field is optional in all circumstances. As noted below, though, this is not the recommended way to make string-based fields optional. null=False, blank=True: This means that the form doesn't require a value but the database does. There are a number of use cases for this: The most common use is for optional string-based fields. As noted in the documentation, the Django idiom is to use the empty string to indicate a missing value. If NULL was also allowed you would end up with two different ways to indicate a missing value. (If the field is also unique, though, you'll have to use null=True to prevent multiple empty strings from failing the uniqueness check.) Another common situation is that you want to calculate one field automatically based on the value of another (in your save() method, say). You don't want the user to provide the value in a form (hence blank=True), but you do want the database to enforce that a value is always provided (null=False). Another use is when you want to indicate that a ManyToManyField is optional. Because this field is implemented as a separate table rather than a database column, null is meaningless. The value of blank will still affect forms, though, controlling whether or not validation will succeed when there are no relations. null=True, blank=False: This means that the form requires a value but the database doesn't. This may be the most infrequently used configuration, but there are some use cases for it: It's perfectly reasonable to require your users to always include a value even if it's not actually required by your business logic. After all, forms are only one way of adding and editing data. You may have code that is generating data that doesn't need the same stringent validation you want to require of a human editor. Another use case that I've seen is when you have a ForeignKey for which you don't wish to allow cascade deletion. That is, in normal use the relation should always be there (blank=False), but if the thing it points to happens to be deleted, you don't want this object to be deleted too. In that case you can use null=True and on_delete=models.SET_NULL to implement a simple kind of soft deletion.

Django模型中的每个选项都有两个目的

在数据库级别定义字段约束(例如SQL, Postgresql，或任何其他) 在表单级别定义字段约束(在数据库层之上的框架级别)

现在让我们回到零和空白

空白是Django表单相关的。它用于在admin或Django中验证Django表单。特别是当我们调用form.is_valid()时 Null与数据库相关。它告诉底层数据库该列是否允许保存空值。

例如，让我们看看下面的例子-

class Company(models.Model):
    name = models.CharField(max_length=100)
    website = models.UrlField()
    founded_on = models.DateField(blank=True, null=False)
    random_date = models.DateFeild(blank=False, null=True)
    random_text = models.TextField(null=True, blank=True)

我已经定义了一个Company模型，它有两个字段，我们在其中玩空白和空选项。让我们看看不同的字段会发生什么

founded_on: can receive an empty string value at form level (framework/language level). While saving to the database then we would raise IntegrityError because the Database will not accept the null value due to null being false. random_date: receiving an empty value at form level (Framework) through validation error, since blank is not allowed due to blank true that is setting constraints at the form level. However, it also allows the column to be null at the database layer. random_text: This is the option that means that the field is allowed to be saved as null at the database layer and also empty string value is allowed to be valid data as per the Django forms validation logic due to blank=True. So in short it can receive empty values (at the framework level and can store empty value at DB level.

要解决所有这些困惑，请将数据库提交视为两层过程。

首先，它填写表单，我们可以在框架级别调用验证数据。 其次，它有一个数据库级别的选项，可以帮助定义DB约束。

这里blank是框架级别的东西，而null是数据库级别的约束。

Null纯粹与数据库相关，而blank与验证相关。如果一个字段为blank=True, Django管理站点的验证将允许输入一个空值。如果一个字段有blank=False，该字段将是必需的