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
    }

Asked By: Hulk

||

Source

Answer 1

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 ...

Answered By: Felix Kling

Answer 2

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")

Answered By: sdornan

Answer 3

this worked for me!

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

Answered By: i_m_brunda

Answer 4

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

Answered By: Sarath Chandran K

Answer 5

len(queryset) also works.

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

if len(sc):
    ....

Answered By: SuperNova

Django check for any exists for a query

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