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
}
This question is related to
python
django
django-views
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 aSELECT COUNT(*)behind the scenes, so you should always usecount()rather than loading all of the record into Python objects and callinglen()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 ...
Update:
it's also possible to use exists():
if scorm.objects.filter(Header__id=qp.id).exists():
....
Returns
Trueif the QuerySet contains any results, andFalseif 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.
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")
this worked for me!
if some_queryset.objects.all().exists(): print("this table is not empty")
Source: Stackoverflow.com