Django isnull ~ SQL IS NULL (original) (raw)

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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.

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