title: Alembic + Sqlalchemy Multi Column Unique Constraint
body: <p>I'm attempting to create using sqlalchemy a multi column unique constraint that will be picked up by Alembic in it's automatic upgrade script generator.</p>
  
  <p>I have create the constraint using:</p>
  
  <p>from sqlalchemy <code>import UniqueConstraint</code> in my model</p>
  
  <pre><code>UniqueConstraint('col1', 'col2', 'number', name='uix_table_col1_col2_col3')
  </code></pre>
  
  <p>However, this is not picked up by Alembic in it's automatic script generation. </p>
  
  <p>I can manually create this in the Alembic script by adding in. </p>
  
  <pre><code>op.create_unique_constraint('uq_table_col1_col2_col3', 'table', ['col1', 'col2', 'col3'])
  </code></pre>
  
  <p>Is there a way to have this be automatically generated by Alembic?</p>
  
  <p>Thank you for your help. </p>