mongo: multiple queries or not?

Question

I'm wondering the best way to query mongo db for many objects, where each one has an array of _id's that are attached to it. I want to grab the referenced objects as well. The objects' schemas looks like this:

var headlineSchema = new Schema({
    title : String, 
    source : String,
    edits : Array       // list of edits, stored as an array of _id's
    ...
});

...and the one that's referenced, if needed:

var messageSchema = new Schema({
    message : String,
    user : String,
    headlineID : ObjectId   // also contains a ref. back to headline it's incl. in
    ...
});

One part of the problem (well, depending if I want to keep going this route) is that pushing the message id's is not working (edits remains an empty array [] afterwards) :

db.headline.update({_id : headlineid}, {$push: {edits : messageid} }, true);

When I do my query, I need to grab about 30 'headlines' at a time, and each one could contain references to up to 20 or 30 'messages'. My question is, what is the best way to fetch all of these things? I know mongo isn't a relational db, so what I'm intending is to first grab the headlines that I need, and then loop through all 30 of them to grab any attached messages.

db.headline.find({'date': {$gte: start, $lt: end} }, function (err, docs) {
    if(err) { console.log(err.message); }
    if(docs) { 
        docs.forEach(function(doc){
            doc.edits.forEach(function(ed){
                db.messages.find({_id:ed}, function (err, msg) {
                    // save stuff
                });
            });
        });
    }
});

This just seems wrong, but I'm unsure how else to proceed. Should I even bother with keeping an array of attached messages? I'm not married to the way I've set up my schema, either. If there is a better way to track relationships between them, or a better query to achieve this, please let me know. Thanks

Answer 1

Does each message belong to only one headline? If so, you can store the headline id as part of each message. Then for each headline, do:

db.messages.find({headline_id: current-headline-id-here})

Answer 2

You could try using the $in operator for selecting a list of ObjectIds

http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24in