Django check for any exists for a query

Question

In django how to check whether any entry exists for a query

sc=scorm.objects.filter(Header__id=qp.id)

This was how it was done in php

if(mysql_num_rows($resultn)) {
    // True condition
    }
else {
    // False condition
    }

Possible duplicate of [what is the right way to validate if an object exists in a django view without returning 404?](http://stackoverflow.com/questions/639836/what-is-the-right-way-to-validate-if-an-object-exists-in-a-django-view-without-r) — Wtower, Apr 17 '17 at 19:40

score 235 · Answer 1 · edited Apr 06 '15 at 11:42

235

As of Django 1.2, you can use exists():

https://docs.djangoproject.com/en/dev/ref/models/querysets/#exists

if some_queryset.filter(pk=entity_id).exists():
    print("Entry contained in queryset")

edited Apr 06 '15 at 11:42

Jossef Harush Kadouri

32,361
10
130
129

answered Feb 01 '12 at 00:17

sdornan

2,805
2
15
7

30

This should be the accepted answer. exists() is generally significantly faster than count(). – frmdstryr Mar 04 '16 at 16:10
2

It also seems to be faster than the `.objects.get(pk=...)` route – Brad Solomon Mar 25 '19 at 17:56

score 119 · Accepted Answer · edited Aug 16 '21 at 08:25

You can use exists():

if scorm.objects.filter(Header__id=qp.id).exists():
    ....

Returns True if the QuerySet contains any results, and False if not. This tries to perform the query in the simplest and fastest way possible, but it does execute nearly the same query as a normal QuerySet query.

Older versions: (<1.2)

Use count():

sc=scorm.objects.filter(Header__id=qp.id)

if sc.count() > 0:
   ...

The advantage over e.g. len() is, that the QuerySet is not yet evaluated:

count() performs a SELECT COUNT(*) behind the scenes, so you should always use count() rather than loading all of the record into Python objects and calling len() on the result.

Having this in mind, When QuerySets are evaluated can be worth reading.

If you use get(), e.g. scorm.objects.get(pk=someid), and the object does not exists, an ObjectDoesNotExist exception is raised:

from django.core.exceptions import ObjectDoesNotExist
try:
    sc = scorm.objects.get(pk=someid)
except ObjectDoesNotExist:
    print ...

@Alex Lebedev: Yes, this method will be available in Django 1.2. Thank you. — Felix Kling, Apr 22 '10 at 20:02

score 1 · Answer 3 · answered Apr 16 '21 at 07:44

Django provides a method called exists() to check if results exists for our query. exists() method return 'True' or 'False'

Class Company(models.Model):
      name = models.CharField(max_length=100)
      year_established = models.DateField()

Class Car(models.Model):
     name = models.CharField(max_length=100)
     company = models.ForeignKey(Company,related_name='car_company',on_delete=models.CASCADE)

following are the queries with exists() method

1. Car.objects.filter(name='tesla').exists()  
2. Company.objects.filter(year_established='date').exists()

using exists in related field - here foreign key

Car.objects.filter(company__name='tesla').exists()

you can give any filter available and use exists() method

score 0 · Answer 4 · answered Sep 28 '20 at 06:50

0

this worked for me!

if some_queryset.objects.all().exists(): print("this table is not empty")

answered Sep 28 '20 at 06:50

i_m_brunda

1
2

score 0 · Answer 5 · answered Jul 09 '21 at 03:29

0

len(queryset) also works.

sc = scorm.objects.filter(Header__id=qp.id)

if len(sc):
    ....

answered Jul 09 '21 at 03:29

SuperNova

25,512
7
93
64

1

you should not use length on a queryset. `.count()` is better but less performant than `.exists()`. Though `.count()` can be useful if you want to retrieve the number of elements in the query – Léo Chaz Maltrait May 18 '22 at 10:11

Django check for any exists for a query

5 Answers5

Linked