backbone identity map

Identity Maps & BackboneBen Teese, Shine Technologies

Thursday, 14 February 13

Overview

The Problem

About Identity Maps

Backbone.IdentityMap


A Demo


The Problem

Roger

fetch

GET /suspects/1

Backend

fetch

GET /suspects

Collection ...

Todd

Michael

Roger


What we want

Roger

fetch

GET /suspects/1

Backend

fetch

GET /suspects

Collection ...

Todd

Michael


Identity Maps


Identity Map

Todd

Michael

Roger

Fred

Suspect:1

Suspect:2

Suspect:3

Suspect:4

......


Object Creation

if class and ID is in identity map return the cached objectelse create new object put it in identity map return the new objectend


Backbone.IdentityMap

Backbone ‘Plugin’

Overrides Model Constructor

Does not alter original Backbone


Before...

var Suspect = Backbone.Model.extend({ ...}); var Suspects = Backbone.Collection.extend({ model: Suspect, url: "/suspects"});

...


After...

var Suspect = Backbone.IdentityMap( Backbone.Model.extend({ ... })); var Suspects = Backbone.Collection.extend({ model: Suspect, url: "/suspects"});

...


How does it work?

Backbone.IdentityMap = function(originalConstructor) { var newConstructor = _.extend(function(attributes, options) { // Execute our identity map logic ... return newOrCachedObject; }, originalConstructor);

return newConstructor;};


How does it work with Backbone?


Backbone.Collection..._prepareModel: function(model, options) { options || (options = {}); if (!(model instanceof Model)) { var attrs = model; options.collection = this; model = new this.model(attrs, options); if (!model._validate(model.attributes, options)) { model = false; } } else if (!model.collection) { model.collection = this; } return model;},...


Backbone.Model

...// Create a new model with identical attributes to this one.clone: function() { return new this.constructor(this.attributes);},...


Caveats

Maps take space

Logout should clear the map

Tests should clear the map

Can’t subclass (yet)


github.com/shinetech


backbone identity map

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