title: Unique key with EF code first
body: <p>I have a following model in my project</p>
  
  <pre><code>public class Category
  {   
      public Guid ID { get; set; }
      [Required(ErrorMessage = "Title cannot be empty")]
      public string Title { get; set; }
  }
  </code></pre>
  
  <p>and I'm trying to make <code>Title</code> as unique key, I googled for the solution, but couldn't find any.
  Can any suggest me how to do it, please?</p>