在django中区分null = True，blank = True [英] differentiate null=True, blank=True in django

问题描述

当我们在django中添加数据库字段时，我们通常会写入 models.CharField（max_length = 100，null = True，blank = True）。与 ForeignKey ， DecimalField 等相同。使用

$ b $的基本区别是什么？ b

1. null = True 只有


2. blank = True 仅


3. null = True ， blank = True CharField ，


$ c> ForeignKey ， ManyToManyField ， DateTimeField ）字段。使用1/2/3的优点/缺点是什么？

解决方案

null = True 在数据库列中设置 NULL （与 NOT NULL ）。 Django字段类型的空值（例如 DateTimeField 或 ForeignKey 将被存储为 NULL 在数据库中。

blank = True 确定表单中是否需要该字段。这包括管理员和您自己的自定义表单。如果 blank = True 则不需要该字段，而如果 False 则该字段不能为空。 p>

两者的组合非常频繁，因为通常如果您要允许一个字段在表单中为空，那么您还需要您的数据库才能允许 NULL 该字段的值。例外情况是 CharField s和 TextField s，Django中永远不会保存为 NULL 。空值作为空字符串存储在数据库中（''）。

几个示例： p>

  models.DateTimeField（blank = True）＃引发IntegrityError如果空白
 
 models.DateTimeField（null = True ）＃NULL允许，但必须填写一个表单
  

显然这两个选项不会使用逻辑意义（尽管如此，如果您希望在表单中始终需要一个字段，但在交易时可选，则可能会为 null = True，blank = False 通过类似shell的对象）。

  models.CharField（blank = True）＃没问题，空白存储为''
 
 models.CharField（null = True）＃NULL允许，但永远不会设置为NULL 
  

CHAR 和 TEXT 类型从不保存为 NULL by Django，所以 null = True 是不必要的。但是，您可以手动将这些字段之一设置为无以强制将其设置为 NULL 。如果您有必要的场景，您应该仍然包含 null = True 。

When we add a database field in django we generally write models.CharField(max_length=100, null=True, blank=True). The same is done with ForeignKey, DecimalField etc. What is the basic difference in having

1. null=True only
2. blank=True only
3. null=True, blank=True

in respect to different (CharField, ForeignKey, ManyToManyField, DateTimeField) fields. What are the advantages/disadvantages of using 1/2/3?

解决方案

null=True sets NULL (versus NOT NULL) on the column in your DB. Blank values for Django field types such as DateTimeField or ForeignKey will be stored as NULL in the DB.

blank=True determines whether the field will be required in forms. This includes the admin and your own custom forms. If blank=True then the field will not be required, whereas if it's False the field cannot be blank.

The combo of the two is so frequent because typically if you're going to allow a field to be blank in your form, you're going to also need your database to allow NULL values for that field. The exception is CharFields and TextFields, which in Django are never saved as NULL. Blank values are stored in the DB as an empty string ('').

A few examples:

models.DateTimeField(blank=True) # raises IntegrityError if blank

models.DateTimeField(null=True) # NULL allowed, but must be filled out in a form

Obviously those two options don't make logical sense to use (though, there might be a use case for null=True, blank=False if you want a field to always be required in forms, but optional when dealing with an object through something like the shell.)

models.CharField(blank=True) # No problem, blank is stored as ''

models.CharField(null=True) # NULL allowed, but will never be set as NULL

CHAR and TEXT types are never saved as NULL by Django, so null=True is unnecessary. However, you can manually set one of these fields to None to force set it as NULL. If you have a scenario where that might be necessary, you should still include null=True.

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