registry.map_imperatively() should be used instead.

Reference: https://docs.sqlalchemy.org/en/14/orm/mapping_api.html?highlight=mapper#sqlalchemy.orm.mapper

This involves some refactoring and updates on almost all chapters. Not sure what is the path (update the book first or the branches). I am available to help.

What needs to be done:

1. Instead of importing MetaData on orm.py, you import his parent (registry):

from sqlalchemy.orm import registry

mapper_registry = registry()

2. On each Table, you pass as second argument mapper_registry.metadata instead of metadata. Eg.:

order_lines = Table(
    "order_lines",
    mapper_registry.metadata,
    Column("id", Integer, primary_key=True, autoincrement=True),
    Column("sku", String(255)),
    Column("qty", Integer, nullable=False),
    Column("orderid", String(255)),
)

3. You add the classes and tables with mapper_registry.map_imperatively instead of mapper. Eg.:

def start_mappers():
    mapper_registry.map_imperatively(model.OrderLine, order_lines)
    ...