pymongo: problem with findandmodify - "no such command" is returned

Question

I believe there is a bug in pymongo (or, at least, the documentation) which makes it impossible to run a findandupdate query.

Here's what happens. When I run:

    result = db.command({
        'findandmodify': 'my_collection',
        'query': {'foo': 'bar'},
        'update': {'$set': {'status': 'queued'}},
    })

The query that actually gets sent to the server is:

{ 'query': {'foo': 'bar'}, findandmodify: 'my_collection', … }

Note that the query argument is first, and findandmodify is second.

But this causes the server to throw up:

OperationFailure: command { 'query': {'foo': 'bar'}, findandmodify: 'my_collection', … } failed: no such cmd

Because the server expects findandmodify to be first (BSON dicts are, apparently, ordered).

Is there any work around for this?

Answer 1

One workaround may be to construct the JavaScript version of the command and pass it to db.eval().

db.eval('db.runCommand({"findandmodify": "my_collection", "query": {"foo": "bar"}, "update": {"$set": {"status": "queued"}},})')

The issue is that, as Alex mentioned, Python dicts have no order, so you will need to build the string more-or-less manually.

Answer 2

For languages that don't have a built-in sorted dict type the mongo drivers include one. In python that is the SON type: http://api.mongodb.org/python/1.4%2B/api/pymongo/son.html. You will need to use that for all commands.

If that still fails make sure you are using the latest version of the database as findandmodify is a new feature.