title: Ember data FixtureAdapter hasmany - Cannot call method 'toString' of undefined
body: <p>again struggling with ember-data >.&lt; , the bug here is on the FixtureAdapter, whenever i use a hasmany relationship, i get the errors <code>Error while loading route: TypeError {}</code>  <code>Cannot call method 'toString' of undefined"</code></p>
  
  <h1>Library versions</h1>
  
  <pre><code>Ember: 1.1.3+pre.e0ffbf84
  Ember Data: 1.0.0-beta.3
  Handlebars: 1.0.0 
  jQuery: 1.9.1 
  </code></pre>
  
  <h1>The code, also <a href="http://jsbin.com/oTIkigAV/3/edit" rel="nofollow">here in a JSBin</a></h1>
  
  <h2>Uncomment the items: hasMany line in the Facture model to reproduce the bug..</h2>
  
  <p>Thanks for the help, it might be a bug, in which case i will post an issue on github.</p>
  
  <pre><code>// Setup
  App = Ember.Application.create({});
  App.ApplicationAdapter = DS.FixtureAdapter;
  
  // Models
  // Facture
  
  App.Facture = DS.Model.extend({
      title: DS.attr(),
      createdAt: DS.attr('date', { defaultValue: new Date() })
      // Comment this line out and it does display a title
      //,items: DS.hasMany('item', { embedded: true })
  });
  
  // - Items
  App.Item = DS.Model.extend({
      desc: DS.attr(),
      qty: DS.attr("number", { defaultValue: 0 }),
      price: DS.attr("string", { defaultValue: 0 })
  });
  
  // FIXTURES
  
  App.Facture.FIXTURES = [
      {
          id: 1,
          title: "Services Informatiques",
          createdAt: new Date(),
          items: [
            { id: 1, desc:'Keay', qty: 2, price: "45" },
            { id: 2, desc:'You kidding', qty: 5, price: "75" }
          ]
      },
      {
          id: 2,
          title: "Intégration Web",
          createdAt: new Date(),
          items: [
            { id: 1, desc:'lkelzekekl', qty: 2, price: "250" },
            { id: 2, desc:'You', qty: 5, price: "200" }
          ]
      }
  ];
  
  // Routes
  App.IndexRoute = Ember.Route.extend({
    model: function(){
        return this.store.find('facture');
    }
  });
  </code></pre>