title: Fetch specific fields on a hasMany relation
body: <p>I have a <strong>hasMany</strong> relation function like this:</p>
  
  <pre><code>public function articles()
  {
      return $this-&gt;hasMany('App\Article');
  }
  </code></pre>
  
  <p>And use it like this:</p>
  
  <pre><code>$data = \App\User::with('articles')-&gt;get();
  </code></pre>
  
  <p>I don't have any problems with it, since it's returning the expected data. Something like this:</p>
  
  <pre><code>{
  "id": 1,
  "name": "Jhon",
  "lastname": "Doe",
  "articles": [
      {
          "id": 1,
          "title": "Article 1",
          "status": "published",
          "published_at": "2015-04-30"
      },
      {
          "id": 2,
          "title": "Article 2",
          "status": "draft",
          "published_at": null
      }
   ]
  }
  </code></pre>
  
  <p>What I am trying to achieve but I still can't it's to fetch just a subset of the relation's fields to obtain this:</p>
  
  <pre><code>{
  "id": 1,
  "name": "Jhon",
  "lastname": "Doe",
  "articles": [
      {
          "id": 1,
          "title": "Article 1"
      },
      {
          "id": 2,
          "title": "Article 2"
      }
    ]
  }
  </code></pre>
  
  <p>My intention is to find a way to specify the subset of fields in the Model's function instead of  iterating the returning collection and unset the unwanted fields.</p>
  
  <p>Is this possible?</p>