Catching a Promise exception and returning a default value

Question

I am having an issue where I want to return a default value if an exception occurs on a promise. The array I return does not seem to work properly.

My Route model hook

model: function() {
    return {
        menuItems : this.store.find('menuItem').catch(function(error) {
            Ember.Logger.error('Retrieving Menu Items', error);
            return [];
        }),

My controller mode

selectFirstMenuItem: function() {
    var model = this.get('model');

    //At this point model.menuItems is some weird object 
    //with an _id : 26, _label : undefined, _result: Array(0), _state : 1 etc. 
    //(maybe a Promise?),  the .get method throws an undefined exception.
    if(model.menuItems.get('length') > 0 ) {
        ...
    }
}.observes('model.menuItems.@each'),

I'm not sure, but maybe the rejection then is fired in this case (...then(func(){}, func(){.. rejected ...})? — enspandi, Mar 12 '15 at 08:21
@EntspAndi I don't follow. Are you suggesting a .then() after the .catch()? — jax, Mar 12 '15 at 10:41
@EntspAndi I think I know what you mean now. .then() accepts two functions, success and failure. I tried that but got the same result. when returning from the failure hook. — jax, Mar 12 '15 at 10:43

score 0 · Accepted Answer · answered Mar 12 '15 at 14:12

You can make this work by returning an Ember.RSVP.hash instead of a regular object containing a promise as follows:

App.IndexRoute = Ember.Route.extend({
  model: function() {    
    return Ember.RSVP.hash({
      menuItems: this.store.find('menuItem').then(
        function(menuItems){ return menuItems; },
        function(error) {
          Ember.Logger.error('Retrieving Menu Items', error);
          return [];
        })
    });
  }
});

And then watching for the length property of menuItems as follows:

App.IndexController = Ember.ObjectController.extend({
  menuItemsObserver: function() {
    var menuItems = this.get('model.menuItems');

    var nonZeroLength = Ember.get(menuItems, 'length');
    if(nonZeroLength ) {
      console.log("The length is NOT zero");
    }
    else {
      console.log("The length is zero");
    }
  }.observes('model.menuItems.length')  
});

Working example here

Catching a Promise exception and returning a default value

1 Answers1