Update only specific fields in a models.Model
I have a model
class Survey(models.Model):
created_by = models.ForeignKey(User)
question = models.CharField(max_length=150)
active = models.NullBooleanField()
def __unicode__(self):
return self.question
and now I want to update only the active field. So I do this:
survey = get_object_or_404(Survey, created_by=request.user, pk=question_id)
survey.active = True
survey.save(["active"])
Now I get an error IntegrityError: PRIMARY KEY must be unique.
Am I right with this method to update?
To update a subset of fields, you can use update_fields:
survey.save(update_fields=["active"])
The update_fields argument was added in Django 1.5. In earlier versions, you could use the update() method instead:
Survey.objects.filter(pk=survey.pk).update(active=True)
Usually, the correct way of updating certain fields in one or more model instances is to use the update() method on the respective queryset. Then you do something like this:
affected_surveys = Survey.objects.filter(
# restrict your queryset by whatever fits you
# ...
).update(active=True)
This way, you don't need to call save() on your model anymore because it gets saved automatically. Also, the update() method returns the number of survey instances that were affected by your update.
.get instead of .filter and this doesn't work. But with filter it works nice. Do you know what is wrong with my code above?
question_id. Where does this value come from? And which exact line does raise the IntegrityError?
question_id comes from urls (?P<question_id>\d+). My fault was that on the working server django 1.4 is installed and my code is 1.5. But with your code it's working fine.
save() (@Alasdair solution) is a safer solution, because this method may triggers things like validation, or any custom code, than update() does not.
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.update()sound deprecated, both update methods are still available and non-deprecated as of Django 4.0. Great answer for mentioning both options, though :-)