title: BigQuery Migration Dynamic Schema on Apache Beam
body: <p>I am trying to write an ETL from Mongo to BigQuery. Since the schema is not fixed in Mongo, I need to update the schema before streaming the data to BigQuery.</p>
  
  <p>So I am using windowing with an side input for the <code>withSchemaFromView</code>.
  When using the windowing for the schema I get an error:</p>
  
  <blockquote>
    <p>Attempted to get side input window for GlobalWindow from non-global
    WindowFn</p>
  </blockquote>
  
  <p>It seems that <code>BigQeryIO</code> uses a global window for the schema. Is there a solution for this?</p>