Naveera A.
The Problem
What is the difference between null=True and blank=True in Django Model Fields?
The Solution
The fundamental difference between these two is that null controls the validation at the database level, and blank is used during form field validation at the application level.
Consider the following model with a title field, a date field, and a time field:
from django.db import modelsclass Book(models.Model): title = models.CharField(max_length=200) pub_date = models.DateField() pub_time = models.TimeField()
By default all fields are required. In order to make a field optional, we have to say so explicitly.
If we want to make the pub_time field optional, we add blank=True to the model, which tells Django’s field validation that pub_time can be empty.
pub_time = models.TimeField(blank=True)
But adding blank=True to the model is not enough. Trying to submit a form based on the model above will result in an integrity error because, while the field validation will accept an empty response, the database will not accept a null value.
To inform our database that the column for this field can be left empty (i.e. null), we need to add null=True in our model:
pub_time = models.TimeField(blank=True, null=True)
Be aware though that if you change the null value of a model field, you will have to create a new migration and apply it, so the database schema is updated to set the NULL or NOT NULL.
An exception to the above is if you are using CharField or TextField. For both of these fields, Django saves an empty string if blank=True. For example, if we want to make the title field optional we can do it like so:
title = models.CharField(max_length=200, blank=True)pub_date = models.DateField()pub_time = models.TimeField(blank=True, null=True)
Although we could still set a null=True on the title field, the Django convention is to avoid using null=True for CharField and TextField since these fields could have two different values for “no data”: None or an empty string "".
