title: Alter Primary Key in Alembic?
body: <p>I've read through <a href="http://alembic.readthedocs.org/en/latest/ops.html">the docs</a>, but I can't find instructions on this anywhere. I tried dropping the old key and adding a new one, but that gets me errors:</p>
  
  <pre><code>op.drop_constraint('PRIMARY', 'some_table', type_='primary')
  op.create_primary_key('PRIMARY', 'some_table', ['col1', 'col2'])
  
  sqlalchemy.exc.OperationalError: (OperationalError) (1025, "Error on rename of ... (errno: 150 - Foreign key constraint is incorrectly formed)") 'ALTER TABLE some_table DROP PRIMARY KEY ' ()
  </code></pre>
  
  <p>What am I doing wrong?</p>