title: Laravel 5.7 exists/unique validation with JSON field type
body: <p>I have a "countries" table with the following fields:</p>
  
  <pre><code>id: integer
  name: json
  </code></pre>
  
  <p>Field "name" stores value as:</p>
  
  <pre><code>{ "en": "Germany", "de": "Deutschland" }
  </code></pre>
  
  <p>I wrote the following rule:</p>
  
  <pre><code>'country' =&gt; 'nullable|string|max:255|exists:countries,name-&gt;en'
  </code></pre>
  
  <p>but it doesn't work like that. How do I make it work?</p>
  
  <p>MariaDB 10.1.36 / Laravel 5.7</p>