当我们在Django中添加模型字段时，我们通常这样写:
models.CharField(max_length=100, null=True, blank=True)
ForeignKey, DecimalField等也是如此。两者的基本区别是什么:
null = True只 空白= True只 null=True, blank=True
对于不同的(CharField, ForeignKey, ManyToManyField, DateTimeField)字段?使用选项1、2或3的优点/缺点是什么?
当前回答
简单地说，
Blank和null不同。
Null是纯粹与数据库相关的，而blank是与验证相关的(表单要求)。
如果null=True, Django将在数据库中存储空值为null。如果字段有blank=True，表单验证将允许输入空值。如果一个字段有blank=False，该字段将是必需的。
其他回答
根据文档，null真正与数据库相关。如果null=true, DB将null输入存储为null。否则，空字符串将被存储为空字符串。 然而，如果blank=true, form将验证它为ok，否则该字段将被form视为“必需”。
默认为false。
简单的null=True定义了数据库应该接受null值，另一方面，空白=True定义了表单验证该字段应该接受空白值或不接受空白值(如果空白=True，则接受该字段中没有值的表单，空白=False[默认值]，则表单验证将显示此字段是必需的错误。
null=与数据库相关的True/False
blank=与表单验证相关的真/假
这就是ORM在Django 1.8中映射空白和空字段的方法
class Test(models.Model):
charNull = models.CharField(max_length=10, null=True)
charBlank = models.CharField(max_length=10, blank=True)
charNullBlank = models.CharField(max_length=10, null=True, blank=True)
intNull = models.IntegerField(null=True)
intBlank = models.IntegerField(blank=True)
intNullBlank = models.IntegerField(null=True, blank=True)
dateNull = models.DateTimeField(null=True)
dateBlank = models.DateTimeField(blank=True)
dateNullBlank = models.DateTimeField(null=True, blank=True)
为PostgreSQL 9.4创建的数据库字段是:
CREATE TABLE Test (
id serial NOT NULL,
"charNull" character varying(10),
"charBlank" character varying(10) NOT NULL,
"charNullBlank" character varying(10),
"intNull" integer,
"intBlank" integer NOT NULL,
"intNullBlank" integer,
"dateNull" timestamp with time zone,
"dateBlank" timestamp with time zone NOT NULL,
"dateNullBlank" timestamp with time zone,
CONSTRAINT Test_pkey PRIMARY KEY (id)
)
为MySQL 5.6创建的数据库字段是:
CREATE TABLE Test (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`charNull` VARCHAR(10) NULL DEFAULT NULL,
`charBlank` VARCHAR(10) NOT NULL,
`charNullBlank` VARCHAR(10) NULL DEFAULT NULL,
`intNull` INT(11) NULL DEFAULT NULL,
`intBlank` INT(11) NOT NULL,
`intNullBlank` INT(11) NULL DEFAULT NULL,
`dateNull` DATETIME NULL DEFAULT NULL,
`dateBlank` DATETIME NOT NULL,
`dateNullBlank` DATETIME NULL DEFAULT NULL
)
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。
正如Django Model Field reference中所说:Link
Field options The following arguments are available to all field types. All are optional. null Field.null If True, Django will store empty values as NULL in the database. Default is False. 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. For both string-based and non-string-based fields, you will also need to set blank=True if you wish to permit empty values in forms, as the null parameter only affects database storage (see blank). Note When using the Oracle database backend, the value NULL will be stored to denote the empty string regardless of this attribute blank Field.blank If True, the field is allowed to be blank. Default is False. Note that this is different than null. null is purely database-related, whereas blank is validation-related. If a field has blank=True, form validation will allow entry of an empty value. If a field has blank=False, the field will be required.
