Django isnull

Summary: in this tutorial, you’ll learn how to use the Django isnull to check whether a value is NULL or not.

Introduction to Django isnull

We’ll use the Employee and Contact models from the HR application for the demonstration. The Emloyee and Contact models map to the hr_employee and hr_contact tables:

In relational databases, NULL denotes missing information. For example, if you don’t know the contact of an employee, you can use NULL for the contact of the employee at the time of recording.

NULL is special because you cannot use the = operator to compare a value with it. Instead, you use the IS operator.

For example, to check if the value in the contact_id is NULL or not, you use the IS operator as follows:

contact_id IS NULLCode language: Python (python)

The IS NULL returns true if the contact_id is NULL or false otherwise.

To negate the IS operator, you can use the NOT operator like this:

contact_id IS NOT NULLCode language: Python (python)

Django uses isnull to check if a value is NUL or not:

Entity.objects.filter(field_name__isnull=True)Code language: Python (python)

The filter() method returns all instances with the field_name is NULL. To negate the isnull, you compare it with False instead:

Entity.objects.filter(field_name__isnull=False)Code language: Python (python)

In this case, the filter() returns all instances of the Entity whose field_name is not NULL.

Django isnull example

The following example uses the isnull to get employees who do not have contacts:

>>> Employee.objects.filter(contact_id__isnull=True)
SELECT "hr_employee"."id",
       "hr_employee"."first_name",
       "hr_employee"."last_name",
       "hr_employee"."contact_id",
       "hr_employee"."department_id"
  FROM "hr_employee"
 WHERE "hr_employee"."contact_id" IS NULLCode language: Python (python)

The generated query use IS NULL operator to compare the contact_id with NULL.

The following example uses the isnull to get all employees who have contacts:

>>> Employee.objects.filter(contact_id__isnull=False) 
SELECT "hr_employee"."id",
       "hr_employee"."first_name",
       "hr_employee"."last_name",
       "hr_employee"."contact_id",
       "hr_employee"."department_id"
  FROM "hr_employee"
 WHERE "hr_employee"."contact_id" IS NOT NULLCode language: Python (python)

In this case, the generated query uses the IS NOT NULL to compare the values in the contact_id column with NULL.

Summary

• Use Django isnull to check if a value is NULL or not.