title: Validating nested json properties in loopback
body: <p>One of my loopback models have structure like:</p>
  
  <pre><code>{
      "name":{
          "first":"sam",
          "last":"billings"
       }
  }
  </code></pre>
  
  <p>Is it possible to "require" validate "first" and "last" properties? I know that first level properties can be validated by giving "required":true, but how can I validate the nested properties? Any help would be appreciated. Thanks in advance!</p>