Mongoose sort by child value - node.js

Question

I have a parent and child schema that looks like:
schedule = Schema ({
from: Date,
to: Date
});
content = Schema ({
schedule: { type: Schema.ObjectId, ref: "schedule" }
name: String
});
My question is, how do I query Mongoose to return "all content, sorted by schedule.from date"?

Answer 1

You'll need to sort in two steps on the client, or store the date fields you want to sort on as embedded fields within the content object.
You're trying to do a collection join by using data from two collections. As MongoDB doesn't support a join, you'd need to populate the schedule field and then do a sort locally on the client. If you have very many documents, or want to do paging of data, this of course won't work.
The most efficient means would be to store the date fields in the content model so that you can perform sorting directly from a single document and collection, without the need of a join. While that may cause other issues with the schema design that you'd like to have, you may find this is the most efficient. The benefit of this denormalization process is that you can do sorting, filtering, etc. very easily and efficiently (especially if you've indexed the date fields for example).
schedule = Schema ({
from: Date,
to: Date
};
content = Schema ({
schedule: { type: Schema.ObjectId, ref: "schedule" },
schedule_data: {
from: Date,
to: Date
},
name: String
});
You could leave the schedule field in the content schema if you wanted to be able to quickly locate and update content documents (or if there were other less used or not needed for sorting/filtering).

Answer 2

In your case, you don't need a reference from one collection to another simply to store schedule.from & schedule.to.
Try the following :
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
mongoose.connect('mongodb://localhost/test');
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function callback () {
console.log('Mongoose connected to MongoDB\n');
content_sch = Schema ({
schedule: {
from: Date,
to: Date
},
name: String
});
var content = mongoose.model('content', content_sch);
contentObj = new content();
contentObj.schedule.from = Date.now();
contentObj.schedule.to = Date.now();
contentObj.name = 'Ryan Rife';
contentObj.save();
//Sorting; -1 to specify an ascending or 1 descending sort respectively
content.find({}).sort({'schedule.from': -1}).exec(function(err,contentDocs){
console.log(contentDocs);
});
});
You can do sorting in many ways another one is as follows which you could try:
content.find({}, null, {sort: {schedule.from: -1}}, function(err, contentDocs) {
//console.log(contentDocs);
});
Check this for more info
When to go for references to documents in other collections?
There are no joins in MongoDB but sometimes we still want references to documents in other collections (schema). Only then you need to use the ObjectId which refers to another schema and from that schema back to the parent.Example:
var personSchema = Schema({
_id : Number,
name : String,
age : Number,
stories : [{ type: Schema.Types.ObjectId, ref: 'Story' }] //Here is a link to child Schema 'Story'
});
var storySchema = Schema({
_creator : { type: Number, ref: 'Person' }, //Field which again refers to parent schema 'Person'
title : String,
fans : [{ type: Number, ref: 'Person' }] //Array which again refers to parent schema 'Person'
});
var Story = mongoose.model('Story', storySchema);
var Person = mongoose.model('Person', personSchema);
For more info check this mongoose populate docs