title: sqlalchemy dynamic schema on entity at runtime
body: <p>I'm using SQL Alchemy and have some schema's that are account specific.  The name of the schema is derived using the account ID, so I don't have the name of the schema until I hit my application service or repository layer.  I'm wondering if it's possible to run a query against an entity that has it's schema dynamically set at runtime?</p>
  
  <p>I know I need to set the <code>__table_args__['schema']</code> and have tried doing that using the type() built-in, but I always get the following error:</p>
  
  <pre><code>could not assemble any primary key columns for mapped table
  </code></pre>
  
  <p>I'm ready to give up and just write straight sql, but I really hate to do that.  Any idea how this can be done?  I'm using SA 0.99 and I do have a PK mapped.</p>
  
  <p>Thanks</p>