I'm learning Backbone.js and reading through the docs I have a hard time understanding the below:
"If a model property is defined, you may also pass raw attributes objects, and have them be vivified as instances of the model."
Looking at Collection#model, they provided the example:
var Library = Backbone.Collection.extend({
model: Book
});
But how do I go on from there and "pass raw attributes objects"?
********Edit***********
Ok looking back now I think what this means is that if I have added the model "Book" to the Library collection, now I can do -
var lib = new Library;
lib.add([
{name: "Curious George"},
{name: "Harry Potter"}
]);
And this will have created 2 models in the lib collection with the corresponding names, right?
Raw object in this case is just a simple object (Not a already constructed model)
In this example, the collection is of type Book (which is a model which might have some predefined attributes and default values)
var Library = Backbone.Collection.extend({
model: Book
});
So Library is a collection Book models.
If you want to create a new Book as part of the Library, you can go about in 2 ways.
1.) Create a Model first and add it to the collection
var book1 = new Book({
id: 1,
name: 'abc'
});
Library.add(book1);
2.) Pass in the Raw attributes to the Collection directly.
Library.add([{id: 1, name: 'abc'}]);
Here's an example that uses Backbone with React.
He defines a Model: var _todos = new Backbone.Model();
And then adds two functions to it:
var TodoStore = _.extend(_todos, {
areAllComplete: function() {
return _.every(_todos.keys(), function(id){
return _todos.get(id).complete;
});
},
getAll: function() {
return _todos.toJSON();
}
});
What I don't understand is why areAllComplete is being applied to a Model instead of to a Collection.
Shouldn't this be a function in a Collection that will get all of its models and check that complete attribute.
Similarly, I would expect getAll to belong to a Collection - get all of its models.
This example seems to replace Collection with Model.
Maybe I don't totally understand how models are used.
That example is using Backbone.Model in a fairly wierd way in my opinion.
This is where it's adding new todos to the store:
var id = Date.now();
_todos.set(id, {
id: id,
complete: false,
text: text
});
}
What it's basically doing is setting every todo-item as an attribute of the Model, using the id as the attribute name. It ends up with _todos.attributes looking something like below
{
"1436600629317": {
"id": 1436600629317,
"complete": false,
"text": "foo"
},
"1436600629706": {
"id": 1436600629706,
"complete": false,
"text": "bar"
}
}
That's the same output you get from _todos.toJSON(). I've no idea why they decided to implement it like that, if they were to try using Backbone.Sync they'd end up with a server API that's not exactly RESTful. It seems strange to use Backbone without leveraging any of the things Backbone provides. There's a reference to the change event here but I don't see it being used anywhere. You could easily reimplement that store using any regular JS object.
The only thing that example seem to be actually using from Backbone is Backbone.Events in the dispatcher. You're totally right that using a Collection would make way more sense because then you could actually make it talk to a REST based server API. That example seems to only use Backbone for the sake of using Backbone.
Here is what I am trying to understand.
Often times I find myself writing backbone like this:
var CallModel = Backbone.Model.extend({
});
var CallsCollection = Backbone.Collection.extend({
model: CallModel,
url: 'url/to/external/json'
});
It is a very basic example but as you can see, there is nothing really in the model all the data is coming into the Collection via an external url call to a json file that is build from a database.
So whats the purpose of the model? I am sure that I am probably not using backbone.js to its fullest extent which is why I am here asking you guys.
First of all, "there is nothing really in the model all the data is coming into the Collection via an external url call" - this is not true.
Let's assume you've the following:
//Model
var CallModel = Backbone.Model.extend({
defaults: {
cost:0,
duration:0
}
});
(without custom attributes or methods, there is no point in extending the original Backbone.Model)
//Collection
var CallsCollection = Backbone.Collection.extend({
model: CallModel,
url: 'url/to/external/json'
});
And the json data returned from service, probably something like:
//Response
{
callSummary: {
missed: 2,
received: 3,
totalCalls:5
totalDuration: 20
}
calls: [{
id:001,
caller:"Mr.A",
callee:"Mr.B",
cost:1,
duration:5
},{
id:002,
caller:"Mr.X",
callee:"Mrs.Y",
cost:1,
duration:7
},{
id:003,
caller:"Mr.A",
callee:"Mrs.B",
cost:1,
duration:8
}],
//and more additional information from your db
}
Now you populate your collection with data by calling it's fetch method:
CallsCollection.fetch();
Your collection should look something like:
{
models: [{
attributes: {
callSummary: {},
calls: [{},{},{}],
...
},
...
}],
length:1,
url: "url/to/external/json",
...
}
The data will be added to a model's attribute hash. If you don't specify a particular model, as Bart mentioned in his answer, backbone will populate the collection with a Backbone.Model instance: Which is still not much useful - Wew... A collection with single model having entire response data inside it's attributes as it is...
At this point, you're wondering why did I even bother creating a model, and then a collection..?
The problem here is Collections are derived from Arrays, while Models are derived from Objects. In this case, our root data structure is an Object (not an Array), so our collection tried to parse the returned data directly into a single model.
What we really want is for our collection to populate its models from the "calls" property of the service response. To address this, we simply add a parse method onto our collection:
var CallsCollection = Backbone.Collection.extend({
model: CallModel,
url: 'url/to/external/json',
parse: function(response){
/*save the rest of data to corresponding attributes here*/
return response.calls; // this will be used to populate models array
}
});
Now your collection will be something like the following:
{
models: [{
...
attributes: {
...
id:001,
caller:"Mr.A",
callee:"Mr.B",
cost:1,
duration:5
}
},{
...
attributes: {
...
id:002,
caller:"Mr.X",
callee:"Mrs.Y",
cost:1,
duration:7
}
},{
...
attributes: {
...
id:003,
caller:"Mr.A",
callee:"Mrs.B",
cost:1,
duration:8
}
}],
length:3,
url: "url/to/external/json",
...
}
This - is what we want! : Now it is very easy to handle the data: You can make use of the add, remove, find, reset and handful of other collection methods effectively.
You can pass this models array into your templating library of choice, probably with two way bindings: When the respective view for one of the call model changes, the particular model will be updated, events will propagate from your models to the collection, and the particular model will be passed into the handler functions.
You can now call fetch, save, destroy, clear and a lot of other methods with ease on single unit's of data (each model), rather than hurdle with the entire data saved in a single model - which is pretty much useless, you've to iterate through the response data manually and perform CRUD and similar operations by your own, and in most cases: re-render the entire collection view. which is very, very bad and totally unmaintainable.
To conclude: If your data source doesn't return an array of objects, or you don't parse the response and return an array of objects from which n number of models are to be populated - Then defining a collection is pretty much useless.
Hopefully, now you get the idea.
Very helpful source of info:
Backbone, The Primer: Models and Collections
Developing Backbone.js Applications
backbonejs.org
You don't need to specify a model. A Backbone collection will default to using Backbone.Model if you don't specify this option. The following would work equally well if you don't need the models of the collection to be of a particular instance.
var CallsCollection = Backbone.Collection.extend({
url: 'url/to/external/json'
});
Reference
EDIT
In essence, specifying the model option within a collection is just a way to ensure that objects added to this collection will be instances of that particular model class. If the models being added to your collection don't have any custom behaviour outside of what is available to Backbone.Model, you don't need to create and specify a model as Backbone collections will default to using an instance of Backbone.Model as I have already mentioned. If, however, you wanted to ensure that models added to a particular collection were of a particular type and shared customized behaviour (e.g. validations, defaults, etc.), you would create your own model class by extending Backbone.Model and specifying this in the collection. I hope this clears things up for you.
Sounds Weird but this is the way.
Every collection in backbone, must represent a model, so basically a collections is a list of models.
Even if your model has no data, you need to indicate it when you create a Collection.
This is how backbone works for collections.
Is there a way to built more complex Model in Backbone.js, let me explain by an example :
This is a Json Session object :
{
id: "17",
notes: "",
start: "2012-10-18T15:57:41.511Z",
end: "2012-10-18T19:22:31.875Z",
sessionType: {
id: "1",
name: "Life Style",
}
}
When retrieving a Session Object from the server, I would like to have a SessionType Backbone.Model in order to add some business logic around this object.
So far I'm only able to retrieve an Object Session with a dummy SessionType, I can't add any logic on it because It doesn't belong to any Backbone model.
You can try this:
window.SessionType = Backbone.Model.extend({
initialize:function () {
},
});
Then in your session model, have a method:
window.Session = Backbone.Model.extend({
initialize:function () {
},
getSessionType () {
return new SessionType(this.get('sessionType'));
}
});
Now you can call the getSessionType() method which returns a model that can have your logic.
#Amulya is 100% correct. However, if you want the Session Model without having to call getSessionType(), I would look at using the the built in parse method and creating your model from there.
If your Session model is related to your model, I would look at using Backbone Relational. Since Backbone does not handle relationships, the plugin listed above does a fine job in filling the gap without too much manual labour.
Normally when I use jquery to build a simple app to show data, I would simply change some global variables depending on certain actions and then when I was ready to retrieve data from the server, I'd pass those vars along to the server.
What is a good way to do this in backbone.js? Does my view handle that? I have this view so far:
var ListView = Backbone.View.extend({
initialize: function() {
this.render();
},
render: function() {
template = _.template("\
<table>\
<% _(collection).each(function(model){%>\
<tr><td><%=model.name%></td><td><%=model.email%></td></tr>\
<%}); %>\
</table>\
");
var context = {collection: this.collection.toJSON()};
$(this.el).html(template(context));
$('#app').html(this.el);
}
});
Basically in my controller I create a users collection and then I use users.fetch() and then pass the users collection to a new ListView object. The initialize function automatically renders (is this bad practice?) I know there's events in backbone.js, and I'm guessing that's where this needs to end up. How do I handle sorting by certain fields or searching for certain text in certain fields or choosing how many results come back (i.e. 10 per page), etc.?
Since backbone.js uses a RESTfull Api it's not so easy. You would have to override the Backbone.sync READ method to construct your own URL call: How to override Backbone.sync?
This might help you as well: REST API Best practices: Where to put parameters?
I would render then, when you have gotten back the data you need. Initialize will be called on var listview = new ListView(), and if you don't have the data bootstrapped - probably nothing will happen.
You can use set the comparator like this:
http://documentcloud.github.com/backbone/#Collection-comparator
var Chapter = Backbone.Model;
var chapters = new Backbone.Collection;
chapters.comparator = function(chapter) {
return chapter.get("page");
};
chapters.add(new Chapter({page: 9, title: "The End"}));
chapters.add(new Chapter({page: 5, title: "The Middle"}));
chapters.add(new Chapter({page: 1, title: "The Beginning"}));
alert(chapters.pluck('title'));
you can use Collection.sort()
http://documentcloud.github.com/backbone/#Collection-sort
or you can use Underscore methods and manually reset the collection
http://documentcloud.github.com/backbone/#Collection-Underscore-Methods
http://documentcloud.github.com/backbone/#Collection-reset