pseudocode for how not to perform datamigrations with SQLAclhemy

invoice_migration.py

import sqlalchemy as sa

invoices_table = sa.Table('invoices', sa.Metadata())

invoices = select([invoices_table]).where(invoice_type='oldie')

for invoice in old_invoices:    
    invoices_table.update(
        ).where(id=invoice.id).values(invoice_type='cutting_edge')
    
    project_to_update = select([projects]).where(invoice.project_id == projects.id)

    project_values = {
        'total_spend':  project_to_update.total_spend,
        'total_projected_spend':  project_to_update.total_projected_spend,
    }
    
    if invoice.status == 'paid':
      project_values['total_spend'] += invoice.amount
    elif invoice.status == 'pending':
      project_values['total_projected_spend'] += invoice.amount
      
    query = projects.update().where(
       projects.c.id == rows_to_update.id
    ).values(project_values)
    
    connection.execute(query)