What's a good Backbone pattern for managing model instances? - backbone.js

Question

I'm trying to minimize server calls by avoiding any requests I can.
Let's say, for the sake of a example, I have a collection of Matchboxes which belong to Users and have Tags assigned, and then also have a collection of Tags and a collection of Users as part of other pages. Getting matchboxes retrieves the user and tag info, so that I can instantiate all required models with one request, accessing the Tags and Users pages retrieves similar collections (only they deal only with their respective models).
My problem: if matchboxes is one page, and tags and users are two other pages, what's a good way to make sure only one model is ever instantiated for any given entity, ie. if I go into users or tags and edit an entry associated with a matchbox the matchbox entry should have the same entry assigned allowing it to listen and react to the updates with out requiring sending requests when going back to the matchbox page in the example.
I've looked over Backbone.relational but it doesn't seem to do what I need, and would rather not wall myself into a framework. So solutions involving patterns are preferable.

Answer 1

Ended up using http://pathable.github.io/supermodel/ which uses the pattern of overwriting the model attribute on collections with a custom function which calls a special Model.create that itself returns an existing (updated with the new values if necessary) instance of said model. The Model.create call has to be used everywhere else in code for unique models.
So essentially every model has a all() method which is a collection of all instances by id. Whenever a model is added it checks it against the collection and returns an existing object if it exists; the data used to instantiate the duplicate is used to update the existing object ensuring data is not stale (which is a nice bonus to the uniqueness I wanted).
The cleanest method seems to be to just wrap the model function into a function that returns it for clearer use; then for every collection that needs to have unique models wrap said model in the function. I came up with this at the moment:
app.single = function (modelPrototype) {
return function (attrs, options) {
return modelPrototype.create(attrs, options);
};
};
(app there is just a scope global, tied to a particular namespace)
So in collections instead of,
model: app.Model
I would then use
model: app.single(app.Model),
Whenever I update a entry in one part of the application the change will trickle down to every other collection/model since if it's the same instance from the user's perspective it's the same instance in code too.
That's about all I could tell from reading the pattern though the code and documentation. Which is sufficient for my own uses.
I suspect this solution would still have some issues if you're caching renders but I haven't found a use for that (prefer to re-render whenever I can to avoid dealing with various artifacts) so it's all good for me.
Unfortunately the codebase seems to be partially abandoned, so while it works with Backbone 1.0.0 (as far as unique models go), I may need to re-create/fork the pattern in future projects.

Answer 2

I think you should think twice about nesting your models and collections in this way, especially if it's primarily for the purpose of easing the bootstrapping of your app. Instead, try to use id's for inter-referencing between models as much as possible. This design problem you have is most likely only the first of many to come if you structure your model/collection tree in a certain way now, only to find it too inflexible later.
That being said, If all you need is for models referencing other models/collections to be able to refer to the same model/collection instance, then simply instantiating them during bootstrap and passing them in to their respective parent models would be sufficient. You could either load some bootstrap data in one request, or preferably inline that data in the HTML:
<script>
var bs_data = {
users : [
...
],
tags : [
...
],
matchboxes : [
...
]
};
</script>
And then instantiate the corresponding models or collections using the bootstap data.
var matchboxes = new Matchboxes();
matchboxes.set(bs_data.matchboxes);
var users = new Users({matchboxes:matchboxes});
users.set(bs_data.users);
The bootstrap data would come from the same backend so your models and collections would already be in sync without having to fetch anything.
As for design patterns; passing dependencies as constructor arguments is actually the dependency injection pattern, albeit more automated solutions to do so exist.

Answer 3

To make sure only one model is ever instantiated, and it is shared among the other elements that use it, being able to listen and update when any of the elements make a change to it, you can use a Singleton pattern. You can read more about it here
If you use Requirejs you can get same effect if you always return the model instantiated. For example:
// the shared model
define([
'jquery',
'underscore',
'backbone'
], function ($, _, Backbone) {
'use strict';
var Model = Backbone.Model.extend({
// ...
});
// return instantiated, so we'll get the same object back whenever we use this model (singleton)
return new Model();
});
// a view using the model
define([
'jquery',
'underscore',
'backbone',
'model'
], function ($, _, Backbone, modelInstance) {
'use strict';
var View = Backbone.View.extend({
initialize: function () {
// listen to what other elements do
this.listenTo(modelInstance, 'eventFromOtherElement', this.doSomething);
// when this element does something, other elements should be listening to that event
modelInstance.trigger('thisViewEvent');
},
doSomething: function () {
// ...
}
});
return View;
});