Django: Is it efficient to save queryset items in loop?

Question

Is it efficient to obtain a queryset, and iterate over it in a conventional loop, saving the changes to each item using save()? e.g.

for mod in mymodel.objects.all():

    # modify
    mod.name = 'new name or whatever'

    # Save
    mod.save()

If not, is there a better way? The docs state that calling save() hits the database which is why I ask. I'm a relative newbie to Django (and Python). In the real case, I will not be iterating over the entire database.

bakkal · Accepted Answer · 2014-09-18 07:43:55Z

2

Not efficient, but sometimes you have to. However you can use .update() especially if it's the same value you want to put in, or if there's an easy way to predict them

so for your example: MyModel.objects.all().update(name='new name'), this won't loop over the entire table, it pretty much translates to UPDATE my_model SET name = 'new name'

You can do a multiple update following a filter too, ref: https://docs.djangoproject.com/en/1.7/topics/db/queries/#updating-multiple-objects-at-once

answered Sep 18, 2014 at 7:43

bakkal

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1 Comment

crobar Over a year ago

Actually my example implied I want the same value in all, but actually this will not be the case. I think you have answered the question though, in my real case it is unavoidable, as I want to note for each item if an attempted action (sending an email) was successful.

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