Support for find_and_modify

[eelkeh]

It would be great to be able to do something like doc = Document.objects.find_and_modify to atomically retrieve and create/modify documents.

[bewt85]

Spooky, I just finished having a go at building this and came here to see if it was something others were interested in including. You can find my rough code in this gist. If this is something others think is valuable, I can start working on some tests using the existing "update" tests which look similar to what we'd want.

What do you think?

[mistresseve666]

Just logged into GitHub to submit an issue to request find_and_modify support.

Great looking work so far, bewt85. Would love to see that included in a future release.

[bewt85]

If this is something that people think would be useful, I'm happy to get writing up some tests. Given how extensive the coverage is for "update" I'd not be keen to invest too much time in this unless it is likely to be of wider interest. What does anyone else think? Ben

[rozza]

@bewt85 I think its worth adding to the core - I commented on your gist but add tests and docs then it in. Doesn't have to be too extensive, I'll try and add more in the future but its a great start.

[ian-beaver]

Any chance of this being integrated into the core soon? It would be nice to have this functionality exposed rather than calling objects._collection.find_and_modify directly.

[KonishchevDmitry]

+1 the previous question. find_and_modify() is a core functionality which is essential in most cases when your application consists more than one host. Please, accept the pull request.

[bewt85]

@rozza I have to admit that I haven't looked at this in almost 9 months but let me know if there are any more tests you want me to add before #421 is mergable and I'll do it as soon as I can get back up to speed. Otherwise I'm happy for this to be closed if you think there are better ways of doing this / it is something that is already being developed elsewhere.

[KonishchevDmitry]

@bewt85, actually #421 doesn't have some find_and_modify()'s features:

• new and remove parameters
• returned fields specification
• doesn't handle pymongo.errors.DuplicateKeyError properly

If you will, you can take a look at my version I wrote yesterday for myself which perfectly works for me:

def modify(self, upsert=False, sort=None, full_response=False, remove=False, new=False, **update):
    """PyMongo's find_and_modify()."""

    if remove and new:
        raise OperationError("Conflicting parameters: remove and new")

    if not update and not upsert and not remove:
        raise OperationError("No update parameters, must either update or remove")

    queryset = self.clone()
    query = queryset._query
    update = transform.update(queryset._document, **update)

    try:
        result = queryset._collection.find_and_modify(
            query, update, upsert=upsert, sort=sort, remove=remove, new=new,
            full_response=full_response, **self._cursor_args)
    except pymongo.errors.DuplicateKeyError as e:
        raise NotUniqueError("find_and_modify() failed ({})".format(e))
    except pymongo.errors.OperationFailure as e:
        raise OperationError("find_and_modify() failed ({})".format(e))

    if full_response:
        if result["value"] is not None:
            result["value"] = self._document._from_son(result["value"])
    else:
        if result is not None:
            result = self._document._from_son(result)

    return result

[claymation]

@KonishchevDmitry that looks great, it's exactly what I'm looking for. Hope we can get it in :)

[KonishchevDmitry]

Hi, everyone! I see Pull Requests started to get accepted again, so I have found a time to shape the code above into a Pull Request - #677. It adds a new QuerySet method to provide find_and_modify() like behaviour. Unlike #421 it provides all pymongo's find_and_modify() features like new=True and remove=True and supports MongoEngine's .only() and .order_by() modifiers. Please consider to merge it.

[MRigal]

Close as it is merged