Ember-data createRecord with hasMany relationship without saving

Question

I want to create a new site record. The model looks like:

var SiteModel = DS.Model.extend({
    name: attr(),
    ...

    languages: DS.hasMany('language'),
});

The language property describes in which languages the content of a site can be written. To create the form, I need to create a model in my route. So I want to create a new record, without saving this one to the db:

 var WebsitesNewRoute = Ember.Route.extend({
     model: function() {
         return this.store.createRecord('site', {
              languages: Ember.A()
         });
     }
 }

That does not work as intended, as I got the following error: cannot set read-only property "languages" on object: <app@model:site::ember1012:null>>. Why is the languages property readOnly? As far as I know I did not configure that in my model...

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I know the question Ember Data- createRecord in a hasMany relationship, but in my case I don't want to save anything yet (I only want to create the model, so I could use it in my template).

Answer 1

Ember-Data defines languages as a read-only property because it doesn't want you to replace the array. No matter if you're saving or not, Ember-Data wants you to add relationships with addObject and remove relationships with removeObject.

So if you wanted to add a language, you would do this:

model: function() {
    var model = this.store.createRecord('site');
    var language = getLanguage();
    model.get('languages').addObject(language);
    return model;
}

What you're doing by giving languages to createRecord, is essentially calling model.set('languages', Ember.A()), and Ember-Data doesn't like that.

It's dumb, I know, but that's just how Ember-Data works.