Sort all the things with mongo and node.js

Sorting shouldn’t be difficult, but through my experience learning meteor I discovered that if mongo likes sort commands one way:

db.posts.find().sort({submitted: -1})

meteor would like them a different way:

Posts.find({}, {sort: {submitted : -1}}

I am adapting one of my meteor projects to use mongo and node.js, connected through mongoose, and fitting in the callback required for node sent me to the google. After a few stackoverflow searches I turned up a several options:

Post.find({}, {sort:[['submitted',-1]]}, function(err, doc) {
  response.send(doc);
});

This option returned a object containing only the entry ids, not the full documents:

0: {_id:2tcte4Srd8QMSqrKt}
1: {_id:5c3FdWphiYiMQzukw}
2: {_id:62vAt5ewucKm542DH}
3: {_id:AWNYsxBgFnv9Z4NSA}
...

Another option suggested that converting the result to an Array would complete the query:

Post.find({},{sort: [['submitted',-1]]}).toArray(function(e, results){
  response.send(results);
});

This option resulted in TypeError: Object #<Query> has no method 'toArray'.

Rather than continuing to search for a snippet to steal, I turned to the source, and it turns out that querying mongo from mongoose is simpler than either of these strategies.

Post.find()
  .sort("-submitted")
  .exec(function(err, doc) {
    response.send(doc);
  });

Success! Why? Because while mongo itself returns a cursor object which can be transformed into documents using toArray(), or fetch() in the case of meteor, mongoose returns a Query object, which will return the full documents once it is passed a callback.

A Query object can be built using method chaining — each method (find | where | limit | select | sort) returns a new Query object, which allows you to build in stages:

Post
.find({ title: /the/ }) // query
.where('cost').gt(17).lt(66)  // query
.where('location').in(['Schnitz', 'Armory'])  // query
.limit(10)  // query
.sort('-ticketDate')  // query
.select('title company')  // query
.exec(callback);  // EXECUTE THE QUERY

Another fun bit of javascript/mongoose magic, is that you can indicate sorting in descending order by prefacing the sort string with a ”-” :

Post
.find({ title: /the/ }) // query
.sort('-ticketDate')  // DESC!
.exec(callback);  // EXECUTE THE QUERY

Awesome.

Resources

mongo docs

stackoverflow