title: Alembic migration: How to set server_onupdate in Alembic's alter_column function
body: <p>I'm trying to change a table column in PostgreSQL using Alembic but I don't know how to perform the needed update to apply the SQLAlchemy's <em>server_onupdate</em> property.</p>
  
  <p>The column is:</p>
  
  <pre><code>changed = Column(ArrowType(timezone=True), server_default=utcnow(), primary_key=True)
  </code></pre>
  
  <p>I'm using the Arrowtype column type from SQLAlchemy_utils package (this is not a problem).</p>
  
  <p>My intention is to create something like this:</p>
  
  <pre><code>changed = Column(ArrowType(timezone=True), **server_onupdate=utcnow()**, primary_key=True)
  </code></pre>
  
  <p>But using the Alembic function: <strong>alter_column</strong></p>
  
  <p>In the documentation there are only references to the <em>server_default</em> property but nothing about <em>server_onupdate</em></p>
  
  <p>Is there a way to achieve this?</p>
  
  <p>Thanks</p>