Both node.js and MongoChef force me to convert to ObjectId. This is what I use to grab a list of users from the DB and fetch a few properties. Mind the type conversion on line 8.
// this will complement the list with userName and userPhotoUrl based on userId field in each item
augmentUserInfo = function(list, callback){
var userIds = [];
var users = []; // shortcut to find them faster afterwards
for (l in list) { // first build the search array
var o = list[l];
if (o.userId) {
userIds.push( new mongoose.Types.ObjectId( o.userId ) ); // for the Mongo query
users[o.userId] = o; // to find the user quickly afterwards
}
}
db.collection("users").find( {_id: {$in: userIds}} ).each(function(err, user) {
if (err) callback( err, list);
else {
if (user && user._id) {
users[user._id].userName = user.fName;
users[user._id].userPhotoUrl = user.userPhotoUrl;
} else { // end of list
callback( null, list );
}
}
});
}