Don't create new version if nothing has changed in Django-reversion

Question

I would like to save new object version only if something has changed, in django-reversion. I went through the documentation and didn't find anything about it. How can I achieve it?

Answer 1

You can use the ignore_duplicates option. Unfortunately

It doesn't follow relations, as that can get expensive and slow very quickly.

If you really want to ignore duplicates for follow relations, you have two possibilities:

1. Do the fork and disable restrictions

Remove and explicit here https://github.com/etianen/django-reversion/blob/master/reversion/revisions.py#L199

Set ignore_duplicates as True by default https://github.com/etianen/django-reversion/blob/master/reversion/revisions.py#L368

Be careful, as mentioned above it can be slow.

2. Listen the post revision commit signal and delete duplicate versions manually

Set ignore_duplicates as False and add the signal receiver:

from django.db import transaction
from django.dispatch import receiver
from reversion.models import Revision, Version
from reversion.signals import post_revision_commit


def clear_versions(versions, revision):
    count = 0
    for version in versions:
        previous_version = Version.objects.filter(
            object_id=version.object_id,
            content_type_id=version.content_type_id,
            db=version.db,
            id__lt=version.id,
        ).first()
        if not previous_version:
            continue
        if previous_version._local_field_dict == version._local_field_dict:
            version.delete()
            count += 1
        if len(versions_ids) == count:
            revision.delete()


@receiver(post_revision_commit)
def post_revision_commit_receiver(sender, revision, versions, **kwargs):
    transaction.on_commit(lambda: clear_versions(versions, revision))

It also can be slow, but you can do it asynchronously (in a Celery task, for example):

# tasks.py

@celery.task(time_limit=60, ignore_result=True)
def clear_versions(revision_id, versions_ids):
    count = 0
    if versions_ids:
        for version in Version.objects.filter(id__in=versions_ids):
            previous_version = Version.objects.filter(
                object_id=version.object_id,
                content_type_id=version.content_type_id,
                db=version.db,
                id__lt=version.id,
            ).first()
            if not previous_version:
                continue
            if previous_version._local_field_dict == version._local_field_dict:
                version.delete()
                count += 1
    if len(versions_ids) == count:
        Revision.objects.only('id').get(id=revision_id).delete()

# signals.py

@receiver(post_revision_commit)
def post_revision_commit_receiver(sender, revision, versions, **kwargs):
    transaction.on_commit(
        lambda: clear_versions.delay(revision.id, [v.id for v in versions])
    )