Question

I’m improving my knowledge about Backbone.js and have this code sample taken from a tutorial. (http://bardevblog.wordpress.com/2012/01/16/understanding-backbone-js-simple-example/)

This example will not access the server for now, so to simulate the retrieval of data from the server I have a file name movies.json.

What I am trying to do:

• Add json data in local storage (using localStorage adapter)
• For this I am using Backbone.ajaxSync, Which Is Given to the alias Backbone.sync by the localStorage adapter: I created the method refreshFromServer () to do this
• The reason for doing this is that I’m trying to implement a way to get data only one time (and only refresh when i need to)

My issues:
  I’m having an error “Uncaught Error: ‘url’ property or function must be specified” when I call refreshFromServer ().
I do not understand why because I set the url collection. (url : “scripts/data/movies.json” )

Sample code

var Theater = {
    Models : {},
    Collections : {},
    Views : {},
    Templates : {}
}

Theater.Models.Movie = Backbone.Model.extend({})
Theater.Collections.Movies = Backbone.Collection.extend({
    model : Theater.Models.Movie,
    localStorage : new Backbone.LocalStorage("MovieStore"), // Unique name within your app.
    url : "scripts/data/movies.json",
    refreshFromServer : function() {
        return Backbone.ajaxSync.apply(this, arguments);
    },
    initialize : function() {
        console.log("Movies initialize")
    }
});

Theater.Templates.movies = _.template($("#tmplt-Movies").html())

Theater.Views.Movies = Backbone.View.extend({
    el : $("#mainContainer"),
    template : Theater.Templates.movies,

    initialize : function() {

        this.collection.bind("reset", this.render, this);
    },

    render : function() {
        console.log("render")
        console.log(this.collection.length);

    }
})

Theater.Router = Backbone.Router.extend({
    routes : {
        "" : "defaultRoute"
    },

    defaultRoute : function() {
        console.log("defaultRoute");
        Theater.movies = new Theater.Collections.Movies()
        new Theater.Views.Movies({
            collection : Theater.movies
        });
        Theater.movies.refreshFromServer();
        //Theater.movies.fetch();
        console.log(Theater.movies.length)
    }
})

var appRouter = new Theater.Router();
Backbone.history.start();

Notes:

• If a comment localStorage property in the collection

  Theater.Models.Movie = Backbone.Model.extend({})
  Theater.Collections.Movies = Backbone.Collection.extend({
  model : Theater.Models.Movie,
  //localStorage : new Backbone.LocalStorage(“MovieStore”)
  …
  });

  and then in router call normal fetch method

  Theater.Router = Backbone.Router.extend({
  routes : {
  “” : “defaultRoute”
  },

  defaultRoute : function() {
  
      Theater.movies = new Theater.Collections.Movies()
      new Theater.Views.Movies({
          collection : Theater.movies
      });
      //Theater.movies.refreshFromServer();
      Theater.movies.fetch();
  }
  

  })

I can see the json list correctly in my view

• If I use the localStorage property in the collection and then call the standard fetch () method, I see only an empty list (I think it is normal as it is read from the local storage and is empty)

• The error only occurs when using the method refreshFromServer () witch use Backbone.ajaxSync (alias for backbone.sync)

Answer 1

Err… my bad. The refreshFromServer implementation is from my answer to your earlier question., and it’s completely, uselessly wrong.

Backbone.sync expects arguments (method, model, options), but as it stands, it doesn’t get what it needs from refreshFromServer because the refresh method simply sends forward whatever arguments it gets. Sorry for the mistake.

The correct, working implementation would be:

refreshFromServer : function(options) {
    return Backbone.ajaxSync('read', this, options);
}

It can be used either via success / error callbacks passed to the options hash:

this.collection.refreshFromServer({ success: function() { /* refreshed... */ });

Or via the jqXHR Promise API:

this.collection.refreshFromServer().done(function() { /* refreshed... */ })

Or not signing up for callbacks and waiting for the collection reset event like in your example:

this.collection.bind("reset", this.render, this);
this.collection.refreshFromServer();

This should work. Please let me know if it doesn’t. I fixed my answer in the previous question too, in case someone stumbles onto it.

Edit: To save the data to local storage after refreshing you need to manually save each of the models:

var collection = this.collection;
collection.refreshFromServer({success: function(freshData) {
    collection.reset(freshData);
    collection.each(function(model) {
        model.save();
    });
}});