new_contents: from sqlalchemy import *
  from migrate import *
  
  def upgrade(migrate_engine):
      # Upgrade operations go here. Don't create your own engine; bind migrate_engine
      # to your metadata
  
      migrate_engine.execute("""
          UPDATE project_need
             SET event_id=NULL
           WHERE event_id=0
      """)
  
  
  def downgrade(migrate_engine):
      # I don't really care about the downgrade for this one.  Who wants invalid
      # data?
      pass
  
subject: Add a migration to fix bad event_id values