{"id":6405,"date":"2023-01-12T09:06:31","date_gmt":"2023-01-12T09:06:31","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=6405"},"modified":"2023-01-12T09:06:32","modified_gmt":"2023-01-12T09:06:32","slug":"django-isnull","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/django-tutorial\/django-isnull\/","title":{"rendered":"Django isnull"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Django isnull<\/code> to check whether a value is NULL<\/code> or not.<\/p>\n\n\n\n

Introduction to Django isnull #<\/a><\/h2>\n\n\n\n

We’ll use the Employee<\/code> and Contact<\/code> models from the HR<\/code> application for the demonstration. The Emloyee<\/code> and Contact<\/code> models map to the hr_employee<\/code> and hr_contact<\/code> tables:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

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

NULL<\/code> is special because you cannot use the =<\/code> operator to compare a value with it. Instead, you use the IS<\/code> operator.<\/p>\n\n\n\n

For example, to check if the value in the contact_id<\/code> is NULL<\/code> or not, you use the IS<\/code> operator as follows:<\/p>\n\n\n

contact_id IS NULL<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The IS<\/code> NULL<\/code><\/code> returns true if the contact_id<\/code> is NULL<\/code><\/code> or false otherwise. <\/p>\n\n\n\n
To negate the IS<\/code> operator, you can use the NOT<\/code> operator like this:<\/p>\n\n\n
contact_id IS NOT NULL<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Django uses isnull to check if a value is NUL<\/code> or not:<\/p>\n\n\n
Entity.objects.filter(field_name__isnull=True<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The filter()<\/code> method returns all instances with the field_name<\/code> is NULL<\/code>. To negate the isnull<\/code>, you compare it with False<\/code> instead:<\/p>\n\n\n
Entity.objects.filter(field_name__isnull=False<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this case, the filter()<\/code> returns all instances of the Entity whose field_name<\/code> is not NULL<\/code>.<\/p>\n\n\n\n
Django isnull example #<\/a><\/h2>\n\n\n\n
The following example uses the isnull<\/code> to get employees who do not have contacts:<\/p>\n\n\n
>>> <\/span>Employee.objects.filter(contact_id__isnull=True<\/span>)\nSELECT \"hr_employee\"<\/span>.\"id\"<\/span>,\n       \"hr_employee\"<\/span>.\"first_name\"<\/span>,\n       \"hr_employee\"<\/span>.\"last_name\"<\/span>,\n       \"hr_employee\"<\/span>.\"contact_id\"<\/span>,\n       \"hr_employee\"<\/span>.\"department_id\"<\/span>\n  FROM \"hr_employee\"<\/span>\n WHERE \"hr_employee\"<\/span>.\"contact_id\"<\/span> IS NULL<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The generated query use IS NULL<\/code> operator to compare the contact_id<\/code> with NULL<\/code>.<\/p>\n\n\n\n
The following example uses the isnull<\/code> to get all employees who have contacts:<\/p>\n\n\n
>>> <\/span>Employee.objects.filter(contact_id__isnull=False<\/span>) \r\nSELECT \"hr_employee\"<\/span>.\"id\"<\/span>,\r\n       \"hr_employee\"<\/span>.\"first_name\"<\/span>,\r\n       \"hr_employee\"<\/span>.\"last_name\"<\/span>,\r\n       \"hr_employee\"<\/span>.\"contact_id\"<\/span>,\r\n       \"hr_employee\"<\/span>.\"department_id\"<\/span>\r\n  FROM \"hr_employee\"<\/span>\r\n WHERE \"hr_employee\"<\/span>.\"contact_id\"<\/span> IS NOT NULL<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this case, the generated query uses the IS NOT NULL<\/code> to compare the values in the contact_id<\/code> column with NULL<\/code>.<\/p>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
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  • Use Django isnull<\/code> to check if a value is NULL<\/code> or not.<\/li>\n<\/ul>\n
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