[Django]-Update multiple objects at once in Django?

by

54👍

✅

Atomic transactions can reduce the time spent in the loop:

from django.db import transaction

with transaction.atomic():
    for i, row in df.iterrows():
        mv = MeasureValue.objects.get(org=row.org, month=month)

        if (row.percentile is None) or np.isnan(row.percentile): 
            # if it's already None, why set it to None?
            row.percentile = None

        mv.percentile = row.percentile
        mv.save()

Django’s default behavior is to run in autocommit mode. Each query is immediately committed to the database, unless a transaction is actives.

By using with transaction.atomic() all the inserts are grouped into a single transaction. The time needed to commit the transaction is amortized over all the enclosed insert statements and so the time per insert statement is greatly reduced.

👤ahmed

37👍

As of Django 2.2, you can use the bulk_update() queryset method to efficiently update the given fields on the provided model instances, generally with one query:

objs = [
    Entry.objects.create(headline='Entry 1'),
    Entry.objects.create(headline='Entry 2'),
]
objs[0].headline = 'This is entry 1'
objs[1].headline = 'This is entry 2'
Entry.objects.bulk_update(objs, ['headline'])

In older versions of Django you could use update() with Case/When, e.g.:

from django.db.models import Case, When

Entry.objects.filter(
    pk__in=headlines  # `headlines` is a pk -> headline mapping
).update(
    headline=Case(*[When(pk=entry_pk, then=headline)
                    for entry_pk, headline in headlines.items()]))
👤Eugene Yarmash

1👍

In my case, we need Value

headlines is a pk -> headline mapping `{1, 'some_val1', 2, 'some_val2', ...}

from django.db.models import Case, When, Value

Entry.objects.filter(
pk__in=headlines  
).update(
headline=Case(*[When(pk=entry_pk, then=Value(headline))
                for entry_pk, headline in headlines.items()]))
👤fromSelect

0👍

Actually, attempting @Eugene Yarmash ‘s answer I found I got this error:

FieldError: Joined field references are not permitted in this query

But I believe iterating update is still quicker than multiple saves, and I expect using a transaction should also expedite.

So, for versions of Django that don’t offer bulk_update, assuming the same data used in Eugene’s answer, where headlines is a pk -> headline mapping:

from django.db import transaction

with transaction.atomic():
    for entry_pk, headline in headlines.items():
        Entry.objects.filter(pk=entry_pk).update(headline=headline)
👤NeilG

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