mongodb - Meteor and DBRefs

Question

I'm using meteor 0.3.7 in Win7(32) and trying to create a simple logging system using 2 MongoDB collections to store data that are linked by DBRef.

The current pseudo schema is :

    Users {
      username : String,
      password : String,
      created  : Timestamp,
    }

    Logs {
      user_id : DBRef {$id, $ref}
      message : String
    }

I use server methods to insert the logs so I can do some upserts on the clients collection.

Now I want to do an old "left join" and display a list of the last n logs with the embedded User name. I don't want to embed the Logs in Users because the most used operation is getting the last n logs. Embedding in my opinion was going to have a big impact in performance.

What is the best approach to achieve this?

Next it was great if possible to edit the User name and all items change theis name

Regards

Answer 1

Playing around with Cursor.observe answered my question. It may not be the most effective way of doing this, but solves my future problems of derefering DBRefs "links"

So for the server we need to publish a special collection. One that can enumerate the cursor and for each document search for the corresponding DBRef. Bare in mind this implementation is hardcoded and should be done as a package like UnRefCollection.

Server Side

    CC.Logs = new Meteor.Collection("logs");
    CC.Users = new Meteor.Collection("users");

Meteor.publish('logsAndUsers', function (page, size) {
    var self = this;
    var startup = true;  
    var startupList = [], uniqArr = [];

    page = page || 1;
    size = size || 100;
    var skip = (page - 1) * size;

    var cursor = CC.Logs.find({}, {limit : size, skip : skip});
    var handle = cursor.observe({
        added : function(doc, idx){
            var clone = _.clone(doc);
            var refId = clone.user_id.oid; // showld search DBRefs
            if (startup){
                startupList.push(clone);    
                if (!_.contains(uniqArr, refId))
                    uniqArr.push(refId);
            } else {
                // Clients added logs
                var deref = CC.Users.findOne({_id : refid});
                clone.user = deref;
                self.set('logsAndUsers', clone._id, clone);
                self.flush();
            }
        },
        removed : function(doc, idx){
            self.unset('logsAndUsers', doc._id, _.keys(doc));
            self.flush();
        },
        changed : function(new_document, idx, old_document){
            var set = {};
            _.each(new_document, function (v, k) {
              if (!_.isEqual(v, old_document[k]))
                set[k] = v;
            });
            self.set('logsAndUsers', new_document._id, set);
            var dead_keys = _.difference(_.keys(old_document), _.keys(new_document));
            self.unset('logsAndUsers', new_document._id, dead_keys);
            self.flush();
        },
        moved : function(document, old_index, new_index){
            // Not used
        }
    });

    self.onStop(function(){
        handle.stop();
    });

    //  Deref on first Run
    var derefs = CC.Users.find({_id : {$in : uniqArr} }).fetch();
    _.forEach(startupList, function (item){
        _.forEach(derefs, function(ditems){
            if (item["user_id"].oid === ditems._id){
                item.user = ditems;
                return false;
            }
        });
        self.set('logsAndUsers', item._id, item);
    });
    delete derefs; // Not needed anymore

    startup = false;
    self.complete();
    self.flush();
});

For each added logs document it'll search the users collection and try to add to the logs collection the missing information. The added function is called for each document in the logs collection in the first run I created a startupList and an array of unique users ids so for the first run it'll query the db only once. Its a good idea to put a paging mechanism to speed up things.

Client Side

On the client, subscribe to the logsAndUsers collection, if you want to make changes do it directly to the Logs collection.

LogsAndUsers = new Meteor.collection('logsAndUser');
Logs = new Meteor.colection('logs'); // Changes here are observed in the LogsAndUsers collection

Meteor.autosubscribe(function () {
    var page = Session.get('page') || 1;
    Meteor.subscribe('logsAndUsers', page);
});