title: Unique Key constraints for multiple columns in Entity Framework
body: <p>I'm using Entity Framework 5.0 Code First;</p>
  
  <pre><code>public class Entity
   {
     [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     public string EntityId { get; set;}
     public int FirstColumn  { get; set;}
     public int SecondColumn  { get; set;}
   }
  </code></pre>
  
  <p>I want to make the combination between <code>FirstColumn</code> and <code>SecondColumn</code> as unique.</p>
  
  <p><strong>Example:</strong></p>
  
  <pre><code>Id  FirstColumn  SecondColumn 
  1       1              1       = OK
  2       2              1       = OK
  3       3              3       = OK
  5       3              1       = THIS OK 
  4       3              3       = GRRRRR! HERE ERROR
  </code></pre>
  
  <p>Is there anyway to do that?</p>