In Django models.py, what's the difference between default, null, and blank?

- `null=True`
- `blank=True`
- `default = 0`


What's the difference? When do you use what?

From [docs][1]:

> `null` If True, Django will store empty
> values as NULL in the database.
> Default is False.
>
> `blank` If True, the field is allowed to
> be blank. Default is False.
>
> `default` The default value for the
> field.

You can use "`default`" to set the value that will be used for the field in question should your code not explicitly set it to a value.

Use "`blank`" for form validation purposes - blank=True will allow the field to be set to an empty value

Use "`null`" if you would like to store an empty value as "null" in the DB. Often it's preferred, however, to set blank values to an empty string or to 0 as appropriate for a given field.

[1]:

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In implementation terms:

The 'blank' field corresponds to all forms. Specifies if this value is required in form and corresponding form validation is done.
'True' allows empty values.

The 'null' field corresponds to DB level. It will be set as NULL or NOT NULL at the DB.

Hence if leave a field empty in admin with blank=true, NULL is fed into the DB. Now this might throw an error if that particular column in the DB is specified as NOT NULL.

**Null**: It is database-related. Defines if a given database column will accept null values or not.

**Blank**: It is validation-related. It will be used during forms validation, when calling form.is_valid().

**Default**: All Time it store the given value(default value) to the field if one doesn't provide any value for this field.

The default values of null and blank are **False**.

That being said, it is perfectly fine to have a field with null=True and blank=False. Meaning on the database level the field can be NULL, but in the application level it is a required field.

Now, where most developers get it wrong: Defining null=True for string-based fields such as CharField and TextField. Avoid doing that. Otherwise, you will end up having two possible values for “no data”, that is: **None** and an empty string. Having two possible values for “no data” is redundant. The Django convention is to use the empty string, not NULL.

Direct from [Django model field reference](

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):

> **`Field.null`**

> If `True`, Django will store empty values as `NULL` in the database. Default is `False`.

> Note that empty string values will always get stored as empty strings, not as `NULL`. Only use `null=True` for non-string fields such as integers, booleans and dates. For both types of 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`).

> Avoid using `null` on string-based fields such as `CharField` and `TextField` unless you have an excellent reason. 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;” Django convention is to use the empty string, not `NULL`.

 

> **`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`, validation on Django’s admin site will allow entry of an empty value. If a field has `blank=False`, the field will be required.

 

> **`Field.default`**

> The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.

I know you already have your answer however till this day it's difficult to judge whether to put `null=True` or `blank=True` or `both` to a field. I personally think it's pretty useless and confusing to provide so many options to developers. Let the handle the nulls or blanks however they want.

I follow this table (from the book "Two Scoops of Django"):
[![When to use null and blank][1]][1]


[![When to use null and blank][2]][2]


[1]:

[2]: