ModelJS

ModelJS is a lightweight model implementation written in Javascript. It supports static methods and properties, instance methods, rudimentary caching, and more.

Defining a Model

Defining a model is easy. The model definition takes a configuration object which can provide four keys for customizing your model:

var User = new Model({
    init: function(attributes){}, // Define a custom init method
    methods: {},                  // Define any instance methods you want
    statics: {},                  // Add any static methods/properties you want
    cacheKey: ""                  // Set up caching (read the "Caching" section below)
});

If you don't specify a custom init method, ModelJS will use a default one for you, which will turn every key in your attributes object into a property of your model instance. A fairly well defined User model might look like:

var User = new Model({
    methods: {
        full_name: function(){
            return this.first_name + " " + this.last_name;
        }
    },
    statics: {
        count: 4,
        alert: function(message){
            // Send the message to all users!
        }
    },
    cacheKey: "id"
});

Using Your Models

ModelJS expects that your model instances are initialized with an "attributes object". You can create and use a new model instance by doing:

var mike = new User({id: 1, first_name: "Mike", last_name: "Trpcic"});

mike.full_name(); // returns "Mike Trpcic"
mike.id // returns 1

Caching

Model.js supports a basic level of caching. If you provide the cacheKey property when defining your model, the model will be given two additional static methods, as well as one instance method. If your cacheKey property maps to a defined instance method, ModelJS will use the return value of that method as the key for caching purposes.

The ModelJS caching system makes heavy use of callback methods. This is intentional, and allows you to pass your callbacks into AJAX calls, so you can asynchronously fetch remote data.

Static Methods
Your class gets two methods, fetch and cache. The fetch method is used to retrieve instances of your model from the cache.

Class.fetch(key, callback, skip_cache);

  // key        => The key that is used to store your object in the cache.
                   This is usually the "cacheKey" property of your instance.
  // callback   => The callback method that will be called and passed your found instance.
  // skip_cache => Tells this fetch request to skip the cache entirely.

When using the caching system, you will need to tell ModelJS where to find instances that it does not already have access to. You do this by defining your own custom fetch method:

var User = new Model({
    statics: {
        fetch: function(key, callback){
            // Implement your custom fetch code here.  This example uses jQuery.
            $.get("/user", {user_id: key}, callback);
        }
    },
    cacheKey: "id"
});

The cache method is used to insert an instance into the cache. Simply call the method and pass it a model instance, and it will be inserted into the cache:

User.cache(mike);

Instance Methods
Every instance of your model will have a default save method. By default, this method only inserts the instance into the appropriate cache. In some cases however, you may want to override the default save function (for example, to push changes to the server). In this case, you can define an instance method called save. Be careful though! If you override this method, you will have to manually insert your object into the cache by calling the Class.cache method mentioned above.

// Using the default method
function userSaved(instance){
    console.log(instance.full_name() + " saved!");
}
mike.save(userSaved);


// using a custom method
var User = new Model({
    methods: {
        save: function(callback){
            // This example uses jQuery
            $.post("/save_user", {}, callback);
            User.cache(this); // Don't forget to manually save this instance to the cache!
        },
        full_name: function(){
            return this.first_name + " " + this.last_name;
        }
    },
    cacheKey: "id"
});

var mike = new User({id: 1, first_name: "Mike", last_name: "Trpcic"});
mike.save(userSaved);

Inheritance

ModelJS supports inheritance via the extend method. This method takes in a configuration block in the same way that a new model definition does:

var Admin = User.extend({
    init: function(attributes){},
    methods: {},
    statics: {},
    cacheKey: ""
});

Your new model will have all the instance and static methods of the parent class, except where you have explicitly overridden them. If you want access to an instance method from the parent class, you can access it via the parent attribute of your instance:

var admin = new Admin({...});

admin.full_name(); // Call the 'full_name' method of the admin class
admin.parent.full_name(); // Call the 'full_name' method of the parent class (User, in this case)

To Do

• Add a way for an instance to "invalidate" itself and remove itself from the cache
• Add a way to turn an entire array of objects into an entire array of instances with one call
• Add a way to fetch multiple instances of a class at once
• Add a test suite

Pull Requests

To make a pull request, please do the following:

• Mention what specific version of ModelJS you were using when you encountered the issue/added the feature. This can be accessed by doing Model.version in a console
• Provide a pastie or gist that demonstrates the bug/feature
• Make sure you update the minified version of the source as well
• Do not modify the Model.version attribute. I will modify that manually when merging the request

Disclaimer

This code is provided without warranty. While I strive to maintain backwards compatibility with previous versions, the code is still under active development. As this is the case, some revisions may break compatibility with earlier versions of the library. Please keep this in mind when using ModelJS.

Copyright and Licensing

Copyright (c) 2012 Mike Trpcic, released under the MIT license