title: Laravel belongsTo with casts not working
body: <p>I have model application and model attributes. <br>
  In table applications, I have column: attributes (type json) In this columns I have ids of attributes. Example:</p>
  
  <pre><code>["5", "6", "7"]
  </code></pre>
  
  <p>This data in table applications in column <code>attributes</code>.</p>
  
  <p>In model applications I writed relation:</p>
  
  <pre><code>protected $casts = [
      'attributes' =&gt; 'array',
  ];
  
  public function attribute() {
      return $this-&gt;belongsTo('App\Attribute', 'attributes');
  }
  </code></pre>
  
  <p>But I get only attribute with id <code>5</code>. But need get all atributes.
  Why I get only one attribute? I tried and with <code>hasMany</code> I get the same result.</p>