|| blank = True || null = True && blank = True

class TestModel(models.Model):
    field1 = models.CharField(max_length=100, null=True)
    field2 = models.CharField(max_length=100, blank=True)   # it's not a correct way
    field3 = models.CharField(max_length=100, null=True, blank=True)

数据库字段:MySQL

CREATE TABLE TestModel (
     `id`        INT(10)        NOT     NULL      AUTO_INCREMENT,

     `field1`    VARCHAR(100)   NULL    DEFAULT   NULL,
     `field2`    VARCHAR(100)   NOT     NULL,
     `field3`    VARCHAR(100)   NULL    DEFAULT   NULL,
)

case-01: null = True

db:   db   field is accepts null value
form: form field is `required`

NB: DB IS ACCEPTS NULL VALUE, BUT FORM FIELD IS REQUIRED. SO FORM IS 
SUBMITTED WHEN THIS FIELD HAVE SOME VALUE. it's good.

case-02: blank = True

db:   db   field is not accepts null value
form: form field is `optional`

NB: FORM IS VALID WITHOUT ANY VALUE, BUT DB IS NOT ACCEPTS NULL VALUE.
SO THE FORM IS SUBMITTED WITHOUT ANY VALUE THEN BOOM. it's worst.

case-03: null = True && blank = True

db:   db   field is accepts null value
form: form field is `optional`

NB: HERE FORM FIELD IS OPTIONAL & FORM IS VALID WITHOUT ANY VALUE 
& DB ALSO ACCEPTS NULL VALUE. SO, IT'S BEST TO USE `null=True && blank=True`

:)

如果设置null=True，它将允许将数据库列的值设置为null。如果你只设置blank=True, django会为这个列设置默认的新值为""。

有一点，null=True将是必要的，即使在CharField或TextField，这是当数据库有唯一的标志设置列。在这种情况下，你需要使用这个:

a_unique_string = models.CharField(blank=True, null=True, unique=True)

最好跳过null=True的非唯一CharField或TextField。否则，一些字段将被设置为NULL，而另一些字段将被设置为“”，并且您必须每次检查字段值是否为NULL。

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.

简单来说就是答案:-

通过null = True，我们告诉数据库模型的这个字段可以为null，通过blank = True，我们告诉Django模型的这个字段可以为null

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。

这里有一个blank= True和null=True字段的示例

description = models.TextField(blank=True, null= True)

在这种情况下: blank = True:告诉我们的表单可以将description字段保留为空

and

null = True:告诉我们的数据库，在我们的db字段中记录一个空值并且不给出错误是可以的。