ObjectId

[agsh]

Do you plan to add a generator for object_ids on the client side?
Without this function when I need an object_id of the last inserted
object I do this:

mongo:insert(Collection, Doc),
Query = [$query-Doc, $orderby-['_id'-(-1)]],
mongo:find_one(Collection, Query, ['_id'-1], ['_id'-object_id(NewRef)]),

But this is ugly...
PS I have checked that mongo:insert allows to set _id on the client
side. It works fine with new _id but does nothing when _id is already
present in db. I think in this case it shall fail with a message or
something.

[khueue]

Thanks for the feedback! And yes, it's been on my list since the beginning. =) The problem boils down to the fact that MongoDB returns nothing upon an insert. As you point out, you can of course create an object id yourself, but that can be tricky. The are several ways to solve this, and I'm not really sure which route(s) I will take:

1. Provide a mongo:insert(+Collection, +Doc, -DocWithId) that basically does what you do in your example (issue a find and instantiate DocWithId).
2. Let bson:doc_get(Doc, '_id', ObjectId) be able to issue a find if the '_id' is not found. I don't really like this idea though, since BSON shouldn't need to know anything about MongoDB.
3. Provide a predicate to generate object ids client-side. This should actually be done sometime anyway (to ease the load on the server).

By the way, I'm curious, what are you using prolongo for? =)

[agsh]

I think the 1st way may be feasible only for one-user application only. For multiple simultaneous Inserts there may be problems with mixing multiple Inserts and Finds. In such cases Find may return an _id of another Insert and is not reliable anymore.
2nd way uses Find as well so it is also not reliable. Consider two Inserts with the same Doc. Find will never differentiate who is who and will return the same _id for both.
3rd way imho is the best. I guess drivers that use MongoDB Wire Protocol solve this problem this way.
Consider this files:
https://github.com/mongodb/node-mongodb-native/blob/master/lib/mongodb/collection.js line 279
and
https://github.com/mongodb/js-bson/blob/master/lib/bson/objectid.js line 187
P.S. I use Prolongo for implementing a compatibility module for Arity/Prolog. Arity/Prolog has advanced abilities for working with Database and BTrees that SWi-Prolog lacks. So I redefined some predicates like record/3, recorded/3, erase and added special predicates like replace, record_before, record_after.