title: ASP.NET Core - Custom model validation
body: <p>In MVC when we post a model to an action we do the following in order to validate the model against the data annotation of that model:</p>
  
  <pre><code>if (ModelState.IsValid)
  </code></pre>
  
  <p>If we mark a property as [Required], the ModelState.IsValid will validate that property if contains a value or not.</p>
  
  <p>My question: How can I manually build and run custom validator?</p>
  
  <p>P.S. I am talking about backend validator only.</p>