title: Backbone-relational cannot instantiate two RelationalModel objects
body: <p>I am trying to implement BackboneRelational and keep getting </p>
  
  <blockquote>
    <p>"Cannot instantiate more than one Backbone.RelationalModel with the
    same id per type!"</p>
  </blockquote>
  
  <pre><code>class App.Models.User extends Backbone.RelationalModel
    urlRoot : '/api/users'
    idAttribute: 'id'
  
    relations: [
      type: Backbone.HasMany
      key: 'plots'
      relatedModel: 'App.Models.Plot'
      collectionType: 'App.Collections.Plots'
      includeInJSON: false
      reverseRelation:
        key: 'user_id',
        includeInJSON: 'id'
    ]
  
  
  class App.Models.Plot extends Backbone.RelationalModel
    urlRoot : '/api/plots'
    idAttribute: 'id'
  </code></pre>
  
  <p>If I switch one of the models to extends Backbone.Model I can instantiate both, but I get all the warnings that the relational functionality is broken..</p>
  
  <p>I am trying to achieve the following:</p>
  
  <pre><code> plot = new App.Models.Plot({id : 700})
   plot.fetch()
   plot.get('user')
  </code></pre>
  
  <p>What am I missing?</p>