Understanding Relationships & Foreign Keys in Mongoose - mongodb

Question

In MongoDB/Mongoose, how do I define a relationship? I think there are a few ways I've seen, but I'm not sure I understand the differences or when do I use which. I am using Mongoose 3
I've defined Todo and TodoList model, where the relationship is obvious. So following the docs http://mongoosejs.com/docs/documents.html, I've defined classes like:
# Todo.coffee
mongoose = require "mongoose"
todoSchema = mongoose.Schema
name: String
desc: String
dueOn: Date
completedOn: Date
module.exports = mongoose.model "Todo", todoSchema
# TodoList.coffee
mongoose = require "mongoose"
Todo = require "./Todo"
todoListSchema = mongoose.Schema
name: String
todos: [Todo.schema]
module.exports = mongoose.model "TodoList", todoListSchema
Then I tried testing the classes:
list = new TodoList
name: "List 1"
todos: [
{ name: "Todo 1", desc: "Hello", dueOn: new Date(2012,10,1), completedOn: new Date(2012,10,2) }
{ name: "Todo 2" }
{ name: "Todo 3", desc: "Hello 2", dueOn: new Date(2012,10,6), completedOn: new Date(2012,10,2) }
{ name: "Todo 4" }
]
#list.todos.push { name: "Todo 5" }
console.log "List", list
list.save (err) ->
if !err
TodoList.find {}, (err, lists) ->
console.log "TODOS"
console.log lists.length, lists
done(err)
else
console.log "ERROR!!!"
done err
When I try to do Todo.find() I get nothing, so the Model (Todo.coffee) is kind of redundant? It looks like Todo are stored in TodoList, as a user I may not care, but I wonder what are the implications? Eg. will the document get too large? 1 TodoList with too many Todos? Does that matter? What if I allow nested Todos (not that I want to do itm just for understanding), is it better to store documents separately then? How do I do that, if I so desire, and when do I do it?
I saw another method, in Mongoose 2 actually. I don't know, if it is possible in 3. Something like using ObjectId instead of nested docs. Maybe thats to store it separately?

Answer 1

I'm still new to Node, Mongoose, and Mongo, but I think I can address at least part of your question. :)
Your current method is the same as I tried doing at first. Basically, it ends up storing it very similarly to this (written in JS, since I don't know CoffeeScript):
var todoListSchema = new mongoose.Schema({
name: String,
todos: [{
name: String,
desc: String,
dueOn: Date,
completedOn: Date
}]
});
I later found this method, which is what I was looking for, and I think what you were intending:
var todoListSchema = new mongoose.Schema({
name: String,
todos: [{
type: mongoose.Schema.Types.ObjectId,
ref: 'Todo' //Edit: I'd put the schema. Silly me.
}]
});
This stores an array of ObjectIds, which you can then load using Query#populate in Mongoose.
I don't know of the technical implications, but it makes more sense in my brain if I keep them separate, so that's what I'm doing. :)
Edit: Here is a some official docs that might be useful: http://mongoosejs.com/docs/populate.html