best practice for data manipulation + validation - backbone.js

Question

I need to store some data in my model which are dates+times in a Unix standard representation (ms from 1970), but what I do is call set by passing a string like "Tue Jul 30 2013 12:25:43 GMT+0200 (CEST)". The string is what I can obtain from my view and I don't really want to convert it in my view, because I think it's a model's duty to do it. By this way the functionalities are well organized and neat. So:
I put this in my model:
initialize: function() {
var self= this;
//conversion of the string date into milliseconds
this.on("change:start_time", function(model, start_time) {
if(start_time !== null){
var data= new Date(start_time);
self.attributes.start_time= data.valueOf();
}
});
...
and it works like a charm. The problems is when you want to set the start_time property and validate it at the same time from one of my views:
this.model.set({
start_time: startDatePicker.getLocalDate()
}, {validate : true});
what's the matter here? Validation is performed before the event handler I set in the initialization is triggered. I found a workaround: moving the conversion into a new function and call it both in the .on and in the validation. But I think something neater is possible. Any suggestion?

Answer 1

The value start_time will be validated before a change event is fired. Also, it is discouraged to set model.attributes directly, instead use set and pass {silent:true} if you don't want a change event fired.
I suggest one of the following methods and get rid of your event handler.
Do the conversion before calling set:
var dt = new Date(startDatePicker.getLocalDate()).valueOf();
this.model.set({
start_time: dt
}, {validate : true});
If you insist that your model does the conversion, another option is over-riding the set method in your model:
var Model = Backbone.Model.extend({
set:function(key,val,options) {
var attrs;
// from Backbone source
if (typeof key === 'object') {
attrs = key;
options = val;
} else {
(attrs = {})[key] = val;
}
if (attrs['start_time'])
attrs['start_time'] = new Date(attrs['start_name']).valueOf();
Backbone.Model.prototype.set.call(this,attrs,options);
}
// your existing code
});
Personally, I would choose the first method.