Stored function used in insert trough PHP runs multiple times - php

Question

I'm trying to understand a strange behavior using PHP with mongodb 2.4.3 win32.
I try to have server side generated sequence ids.
When inserting documents using a stored function as one of the parameters it seems that the stored function is called several times at each insertion.
Let's say I have a counter initialized like this:
db.counters.insert( { _id: "uqid", seq: NumberLong(0) } );
I have a stored function named getUqid which is defined as
db.system.js.save(
{ _id: "getUqid",
value: function () {
var ret = db.counters.findAndModify(
{ query: { _id: "uqid" },
update: { $inc: { seq: NumberLong(1) } },
new: true
} );
return ret.seq;
}
} );
When I do three insertions like this:
$conn->test->ads->insert(['qid' => new MongoCode('getUqid()') , 'name' => "Sarah C."]);
I get something like that:
db.ads.find()
{ "_id" : ObjectId("51a34f8bf0774cac03000000"), "qid" : 17, "name" : "Sarah C." }
{ "_id" : ObjectId("51a34f8bf0774cac03000001"), "qid" : 20, "name" : "Michel D." }
{ "_id" : ObjectId("51a34f8bf0774cac03000002"), "qid" : 23, "name" : "Robert U." }
Any clue why qid is getting stepped by 3 ? It should mean that I received three call to my stored function right ?
Thanks in advance for your help, Regards.
PS: secondary question: are NumberLong still required to be sure we have 64bit unsigned integer in internal mongodb storage ? Any command to cross-check that in the shell ?

Answer 1

Cross-referencing this question with PHP-841. From the PHP side of things, you're actually storing a BSON code value in the qid field. You can likely verify that when fetching results back from the database or doing a database export with the mongodump command.
The issue is with the JS shell wrongfully evaluating the code type upon display, and that's the point where findAndModify is executed. This fix should be included in a subsequent server release.
In the meantime, Sammaye's suggestion to call findAndModify from PHP is the best option for this sort of functionality. Coincidentally, it is also what is done in Doctrine MongoDB ODM (see: IncrementGenerator). It does require an additional round trip to the server, but that is necessary since MongoDB has no facility for executing JS callbacks during a write operation.
If minimizing the round-trips to MongoDB is of utmost importance, you could insert the documents by executing server-side JS through PHP with MongoDB::execute() and do something like returning the generated ID(s) as the command response. Of course, that's generally not advisable and JS evaluation has its own caveats.