title: Fluent-NHibernate: How to a create a many-to-many relationship with a unique contraint
body: <p>I want to create a many to many relationship, but I want to have in the new table(MessageReceivers) a unique contraint on both columns (AdvanceMessageId,UserId):</p>
  
  <pre><code>mapping.HasManyToMany(x =&gt; x.Receivers)
         .WithParentKeyColumn("AdvanceMessageId")
         .WithChildKeyColumn("UserId")
         .Cascade.All()
         .LazyLoad()
         .WithTableName("MessageReceivers");
  </code></pre>
  
  <p>Thanks for help</p>