title: CakePHP 3 not saving hasOne associations
body: <p>I have two models - <code>Cars</code> and <code>CarOptions</code></p>
  
  <p><code>Cars</code> hasOne <code>CarOptions</code></p>
  
  <p>If the user were to edit Cars - they can also set some CarOptions and save</p>
  
  <p>Everything related to <code>Cars</code> saves just fine, but <code>CarOptions</code> does not save. If I were to debug the <code>Car</code> object just before save - I see the following</p>
  
  <pre><code>Car: {
      "id": 3,
      "name": "Ford Mustang",
      "description": "some description",
      "city": "San Francisco",
      "state": "California",
      "country": "USA",
      "created": "2015-08-14T12:20:14-0500",
      "CarOptions": {
          "manual_transmission": "N"
      }
  }
  </code></pre>
  
  <p>My code to save is as below</p>
  
  <pre><code>$car = $this-&gt;Cars-&gt;findByName('Ford Mustang')-&gt;first();
  $car = $this-&gt;Cars-&gt;patchEntity($car, $this-&gt;request-&gt;data);
  $carOptions = $this-&gt;Cars-&gt;CarOptions-&gt;newEntity();
  $carOptions-&gt;manual_transmission = 'N';
  $car-&gt;CarOptions = $carOptions;
  $this-&gt;Cars-&gt;save($car);
  </code></pre>
  
  <p>However the CarOptions record is not created or edited. What am I missing?</p>