title: How to create two-column unique key constrain with HBM mapping?
body: <p>I have a hibernate mapping:</p>
  
  <pre>
  &lt;properties name="lrt_bps_bpr_acs_uk" unique="true">
      &lt;many-to-one name="activitySummary" column="bps_acs_id" class="xyz.ActivitySummary"
      unique-key="lrt_bps_bpr_acs_uk"/>
      &lt;many-to-one name="bestPractice" column="bps_bpr_id" class="xyz.BestPractice" 
          unique-key="lrt_bps_bpr_acs_uk"/>
  &lt;/properties>
  </pre>
  
  <p>I expected that hibernate would create unique constraint on database for this mapping. Nothing like that happened however.</p>
  
  <p>What am I doing wrong?</p>