{"id":6438,"date":"2023-01-18T02:23:34","date_gmt":"2023-01-18T02:23:34","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=6438"},"modified":"2023-01-18T02:27:56","modified_gmt":"2023-01-18T02:27:56","slug":"django-exists","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/django-tutorial\/django-exists\/","title":{"rendered":"Django exists"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Django QuerySet<\/code><\/code> exists()<\/code> method to check if a QuerySet<\/code><\/code> contains any rows.<\/p>\n\n\n\n

Introduction to the Django QuerySet exists() method #<\/a><\/h2>\n\n\n\n

Sometimes, you want to check if a query contains any rows. To do it, you use the exists()<\/code> method of the QuerySet<\/code> object.<\/p>\n\n\n\n

The exists()<\/code> method returns True<\/code> if the QuerySet<\/code> contains any rows or False<\/code> otherwise.<\/p>\n\n\n\n

Behind the scenes, the exists()<\/code> will attempt to perform the query in the fastest way possible. However, the query will be nearly identical to a regular QuerySet<\/code> query.<\/p>\n\n\n\n

Suppose you have a QuerySet<\/code> and want to check if it has any objects. Instead of doing this:<\/p>\n\n\n

if<\/span> query_set:\n   print('the queryset has at least one object'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
…you should use the exists()<\/code> because it is a little bit faster:<\/p>\n\n\n
if<\/span> query_set.exists():\n   print('the queryset has at least one object'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Django 4.1 added the aexists()<\/code><\/code> which is an asynchronous version of exists()<\/code>.<\/p>\n\n\n\n
Django exists() method example #<\/a><\/h2>\n\n\n\n
We’ll use the Employee<\/code> model for the demonstration. The Employee<\/code> model maps to the hr_employee<\/code> table in the database:<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
First, run the shell_plus<\/code> command:<\/p>\n\n\n
python manage.py shell_plus<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, find the employees whose first names start with the letter J<\/code>:<\/p>\n\n\n
>>> Employee.objects.filter(first_name__startswith='J').exists()\nSELECT<\/span> 1<\/span> AS<\/span> \"a\"<\/span>\n  FROM<\/span> \"hr_employee\"<\/span>\n WHERE<\/span> \"hr_employee\"<\/span>.\"first_name\"<\/span>::text<\/span> LIKE<\/span> 'J%'<\/span>\n LIMIT<\/span> 1<\/span>\nExecution time<\/span>: 0.000000<\/span>s [Database<\/span>: default<\/span>]\nTrue<\/span><\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that Django generated the SQL based on the PostgreSQL. If you use other databases, you may see a slightly different SQL statement.<\/p>\n\n\n\n
In this example, the exists()<\/code> method returns True. It selects only the first row to determine whether the QuerySet<\/code> contains any row.<\/p>\n\n\n\n
If you do not use the exists()<\/code> method, the QuerySet<\/code> will get all the rows from the hr_employee<\/code> table:<\/p>\n\n\n
>>> qs = Employee.objects.filter(first_name__startswith='J') \n>>> print(qs.query)\nSELECT<\/span> \"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>\nFROM<\/span> \"hr_employee\"<\/span>\nWHERE<\/span> \"hr_employee\"<\/span>.\"first_name\"<\/span>::text<\/span> LIKE<\/span> J%\nORDER<\/span> BY<\/span> \"hr_employee\"<\/span>.\"first_name\"<\/span> ASC<\/span>,\n         \"hr_employee\"<\/span>.\"last_name\"<\/span> ASC<\/span><\/code><\/span>Code language:<\/span> SQL (Structured Query Language)<\/span> (<\/span>sql<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • Use the Django exists()<\/code> method to check if a QuerySet<\/code> contains any rows.<\/li>\n<\/ul>\n
    \n\t
    \n\t\t
    Was this tutorial helpful ?<\/div>\n\t\t
    \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
    \n\t\t
    \n\t\t\t
    <\/div>\n\t\t\t