A "url" property or function must be specified backbone.js save

Question

I would like to perform the update operation as seen in the function. But when updating, the city.save () function returns me the error in the screen image and header. Why could it be ? Can you help me.

define(['text!components/wseducationconfirm/wseducationConfirmTemplate.html'], function (template) {
        var cityTemplate = Handlebars.compile(template);

var CityModel = Backbone.Model.extend({});

var CityCollection = Backbone.Collection.extend({
    url: "/api/epermit",
    model: CityModel
});
return Backbone.View.extend({

    el: "#content",
    initialize: function () {
        this.cities = new CityCollection();
        this.listenTo(this.cities, "reset add change remove", this.render);
        this.cities.fetch({reset: true});

    },
    events: {
        'click .confirmEntryPermit':'confirmEntryPermit'
    },
    confirmEntryPermit: function (e) {
        var value = 1;
        var id = $(e.currentTarget).data("id");
        var city = this.cities.findWhere({epermitId: id});
        city.set({wsEducation:value});
        city.save();
    },
    render: function () {
        for(var i = 0;i<this.cities.length;i++){

            var exdate =   new Date(this.cities.models[i].get("exitDate")).toISOString();
            exdate = exdate.substr(0,10);
            var endate = new Date(this.cities.models[i].get("entryDate")).toISOString();
            endate = endate.substr(0,10);

            if(this.cities.models[i].get("wsEducation") == 1){
                this.cities.remove(this.cities.models[i]);
            }else{
                this.cities.models[i].set({exitDate:exdate});
                this.cities.models[i].set({entryDate:endate});
            }
        }
        this.$el.html(cityTemplate({cities: this.cities.toJSON()}));
    }
  });
});

Answer 1

Models require an id attirubute in order to derive a url from the collection's url. You can fix this by setting {idAttirubute : 'epermitId'} in model options