I have a webapp based on Backbone.js with a list. The entries of the list are coming from a REST API. This list (JSON array) updates from time to time. I want to update my list in the frontend too, without reloading the page.
I thought about using a poller to update the file list with every new object returned by the API. However, the poller is not the problem here, I first need a function to add just the new models to the file list.
The API returns a JSON list, based on this model:
Xff = Backbone.Model.extend({
defaults: {
id: null,
name: "",
language: "en",
timestamp: 0,
status: null,
progress: 10,
duration: 0
}
});
This is the collection. restUri points to the REST API and with /files it gets the complete file list.
XffCollection = Backbone.Collection.extend({
model: Xff,
comparator: function(a, b) {
return (a.get("timestamp") > b.get("timestamp") ? -1 : 1);
},
url: restUri + "files"
});
This is the AppView object. It uses the XffCollection, as explained above.
app = new AppView({
collection: new XffCollection()
});
AppView is a regular backbone view...
AppView = Backbone.View.extend({ .... })
Using app.collection.fetch() I can fire the request (visible in firebug), but the list is not updated. I also have a addAll() function, but then it just appends the new file list to the old file list.
The addAll:
addAll: function() {
this.collection.chain().sort().each(this.addOne, this);
}
This is the addOne:
addOne: function(xff) {
var v = new XffView({model: xff});
this.xffViews.push(v);
$("#xffs").append(v.render().el);
}
How can I add just the new entries to the list?
UPDATE
While kindasimples anwser works now, the filelist in the frontend is not sorted anymore using the comparator defined in the collection (with the timestamp). Using addAll() in the bottom of the comparator, the list is sorted.
To provide additional information, here are more parts of the overall backbone code: http://pastebin.com/rR39x3Y1
From the backbone.js docs:
collection.sort([options])
Force a collection to re-sort itself. You don't need to call this under normal circumstances, as a collection with a comparator will sort itself whenever a model is added. To disable sorting when adding a model, pass {sort: false} to add. Calling sort triggers a "sort" event on the collection.
But it does not sort itself. Also calling app.collection.sort() right after the fetch does not help.
UPDATE 2
I fixed it by sorting the array in the API before returning it. That's not how it was meant to be but at least it works now.
You have the right idea. addOne() will render individual items when you do your initial setup after a fetch to populate items. You can add a listener to the collection events to add the new items. Collection.Fetch does what you want by adding new models to the collection and leaving the old in tact (as long as you don't pass the {reset:true} flag as a parameter)
So, on your view add the listener to the initialize hook
initialize: function() {
this.listenTo(this.collection, "add", this.addOne)
}
You will probably want to define the idAttribute on your Xff Model so that backbone can identify new items properly.
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.
Trying to populate a Collection from a list of values, I am getting an error about the Collection's model's prototype being undefined. Looking at this question about a similar problem, I have checked that the Model is actually created before the collection is instanced, to the best of my ability.
The error is being thrown in one of the event handlers of the Marionette CompositeView that holds the Collection, after fetching the data from the server and trying to reset the collection with the list of values from the data which should be populated into it.
Note: Using Backbone 0.9.10
The Model
MyItemModel = Backbone.Model.extend({});
The Collection
MyCollection = Backbone.Collection.extend({
model: MyItemModel
});
The CompositeView's relevant code
MyCompositeView = Backbone.Marionette.CompositeView.extend({
initialize: function(options) {
_.bindAll(this);
this.model = new MyCompositeViewModel();
this.collection = new MyCollection();
},
//This event handler gets properly fired and run.
on_event: function() {
var that = this;
// The data comes through fine with this `fetch`
this.model.fetch({success: function() {
var collection_results= that.model.get("collection_results");
// The error fires in this line
that.collection.reset(collection_results);
that.render();
});
}
})
The error
The error happens in the add function in Backbone, when doing a get for the model object, checking to see if it is a duplicate. The failing code is here:
// Get a model from the set by id.
get: function(obj) {
if (obj == null) return void 0;
// The error originates from this line
this._idAttr || (this._idAttr = this.model.prototype.idAttribute);
return this._byId[obj.id || obj.cid || obj[this._idAttr] || obj];
},
this._idAttr || (this._idAttr = this.model.prototype.idAttribute);
Here, the this.model.prototype.idAttribute fails because the prototype for the model is not defined.
Why is this happening, and how can it be fixed?
Thanks a lot!
The reason is, in Babkbone 0.9.10, if you call collection.reset(models) without options, the models will be passed to collection.add() which strictly needs real models as argument.
But, in fact, the arguments you passed are not real models. They are just an array of hash attributes.
Two options to fix:
Option 1: Call the reset with a parse option
that.collection.reset(collection_results, {parse: true});
Then reset will parse the array of hashes and set them as model.
Option 2: Upgrade to latest version Backbone 1.1.0.
Here reset() no longer pass responsibility to add() but use set() smartly. This option is recommended. And you don't need options here.
that.collection.reset(collection_results)
Another point
May I suggest you not to define model in CompositeView? CompositeView is for collection, not model. Of course I understand the model here is just to hold and fetch some data, but it would be really confusing for the code to be read by another developer, as well as your own maintaining.
To get bootstrapped data, you can load the data at first request and use conventional way to put it into collection. http://backbonejs.org/#FAQ-bootstrap
Every time I call "this.model = new Unidade();", this.model keeps some values of the last value stored in there.
this.model.id => turns to null, but others properties keep the values of the last model.
Model Source
window.Unidade = Backbone.Model.extend({
urlRoot : $urlPadrao + "cliente/externo/unidade",
defaults: { // setting defaults to null or ""
},
initialize: function () {
... // Just initialize the validators methods
},
getDefaults: function() {
// returns the same values of defaults
// since I can't get a "new" model
}
});
In my view:
this.model = new Unidade();
// this.model may be already populated... I'm trying to create a new one
// that's the problem, it keeps some values of the last one
// Shouldn't give me a new model populate with the defaults?
For the record I'm not messing with the prototypes.
I manage to get the source of this sorcery, somehow, backbone was getting these properties and setting then on the prototype of the model, thus making them static.
Mighty strange.
By any chance are these properties arrays? I found that mine were essentially being treated as pass-by-reference due to what I found in this article :
Arrays in a Backbone.js Model are essentially static?
In this stackoverflow post i read about filtering backbone collections and using subsets.
One answer (by sled) recommends using backbone.subset.js (usage example).
I could not find any further resources on backbone.subset.js and I failed implementing it into my project.
It seems like backbone.subset.js is the perfect solution for what i'm trying to achieve.
(Having one "parent" collection that holds all models at all times, and depending on user input filtering the relevant models from the parent collection into a backbone.subset collection.)
My "parent" collection, holding all tasks:
var TasksAll = Backbone.Collection.extend({
url: '/tasks', // the REST url to retrieve collection data
model: Task // the models of which the collection consists of
});
var allTasks = new TasksAll();
Now i want to create a subset collection for e.g. tasks where task.status = 0:
var TasksTrash = new Backbone.Subset({
superset: allTasks,
filter: function(Task) {
return Task.isTrash();
}
});
var trashTasks = new TasksTrash();
Whereas inside the Task model, the method "isTrash" returns true if:
this.get('status') == 0
a) Are there any more resources on backbone.subset.js?
b) How do I implement above scenario?
c) Can I pass 'superset' and 'filter' options as params to the Backbone.Subset init function?
d) I looked into the backbone.subset.js code, when I 'reset' my parent Collection my subset Collections should be updated straight away, right?
PS: I'm fairly new to Backbone. Thanks for your help.
Looking at the source for backbone-subset, it looks as though there is a pre-initialization hook which you could utilize in order to make the 'sieve' or filter available as an option or argument:
https://github.com/masylum/Backbone.Subset/blob/master/backbone.subset.js#L50
As for providing parent as an argument, there is an outstanding patch to add that exact functionality:
https://github.com/masylum/Backbone.Subset/pull/5
With it, you can pass in parent as an option, if it is not an option the library will fall back to looking for it on the object Prototype