Question

I’m using Backbone and Marionette, I’m retrieving my models from a backend.
The models belong to a collection.
The problems are:

1) The validate method is never called unless explicitly from within the initialize. Why?
2) When I explicitly call the validate method, it correctly returns for an invalid model I created for testing. But I am not able to catch the “invalid” event. What am I doing wrong?

Here’s the model:

 var Job = Backbone.Model.extend({
    validate: function(attrs){
        if (! attrs.title ) {
            return "A job should have a title";
        }
    },

    initialize: function(){

        this.validate(this.attributes); //manual call to validate
        this.on("invalid",  function(model, error){ //never executed even when the validate model returns the error string
            console.log(error);
        });

    }

});

And here the Collection:

var JobList = Backbone.Collection.extend({
        model: Job,
        url: '/api/1.0/jobs/',
        parse: function(response) {
          return response.results;
        }

    });

Answer 1

The validation logic was changed in Backbone 0.9.10. Quoting from the change log, validation now works as follows:

Model validation is now only enforced by default in Model#save and no longer enforced by default upon construction or in Model#set, unless the {validate:true} option is passed.

So if you want the model to be validated upon initialization or set, you need to pass the option validate:true to the constructor / method.

The reason you are not receiving the invalid event when you manually call your model.validate method is that Backbone is not performing any of the validation when you do. You call a method you defined on the model, and Backbone doesn’t know anything about it.

Model validation in Backbone is convention based in the sense that Backbone doesn’t define a method called validate on the model – you do yourself. However, if you have defined such a method, Backbone will call it for you when validation occurs (on save, or in constructor/setter with validate:true, and the invalid event will be triggered.