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?

Direct from Django model field reference:

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.

From docs:

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.

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"):