title: Unique Constraint Over Multiple Columns
body: <p>I am using SEAM 2/Hibernate along with PostgreSQL 9 database. I have the following table</p>
  
  <pre><code>Active Band
  ===========
  active_band_id serial
  active_band_user text
  active_band_date timestamp
  active_band_process integer
  </code></pre>
  
  <p>I would like to add a constraint that ensures each new entry has a unique combination of active_band_user and active_band_date.</p>
  
  <p>There could potentially be many attempted inserts per second so I need this to be as efficient as possible, is there a SEAM / hibernate annotation I can use in the entity mapping?</p>
  
  <p>Thanks in advance</p>