"""Same example as basic_association, adding in
usage of :mod:`sqlalchemy.ext.associationproxy` to make explicit references
to ``OrderItem`` optional.
"""
from datetime import datetime
from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import DateTime
from sqlalchemy import Float
from sqlalchemy import ForeignKey
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
Base = declarative_base()
class Order(Base):
__tablename__ = "order"
order_id = Column(Integer, primary_key=True)
customer_name = Column(String(30), nullable=False)
order_date = Column(DateTime, nullable=False, default=datetime.now())
order_items = relationship(
"OrderItem", cascade="all, delete-orphan", backref="order"
)
items = association_proxy("order_items", "item")
def __init__(self, customer_name):
self.customer_name = customer_name
class Item(Base):
__tablename__ = "item"
item_id = Column(Integer, primary_key=True)
description = Column(String(30), nullable=False)
price = Column(Float, nullable=False)
def __init__(self, description, price):
self.description = description
self.price = price
def __repr__(self):
return "Item(%r, %r)" % (self.description, self.price)
class OrderItem(Base):
__tablename__ = "orderitem"
order_id = Column(Integer, ForeignKey("order.order_id"), primary_key=True)
item_id = Column(Integer, ForeignKey("item.item_id"), primary_key=True)
price = Column(Float, nullable=False)
def __init__(self, item, price=None):
self.item = item
self.price = price or item.price
item = relationship(Item, lazy="joined")
if __name__ == "__main__":
engine = create_engine("sqlite://")
Base.metadata.create_all(engine)
session = Session(engine)
# create catalog
tshirt, mug, hat, crowbar = (
Item("SA T-Shirt", 10.99),
Item("SA Mug", 6.50),
Item("SA Hat", 8.99),
Item("MySQL Crowbar", 16.99),
)
session.add_all([tshirt, mug, hat, crowbar])
session.commit()
# create an order
order = Order("john smith")
# add items via the association proxy.
# the OrderItem is created automatically.
order.items.append(mug)
order.items.append(hat)
# add an OrderItem explicitly.
order.order_items.append(OrderItem(crowbar, 10.99))
session.add(order)
session.commit()
# query the order, print items
order = session.query(Order).filter_by(customer_name="john smith").one()
# print items based on the OrderItem collection directly
print(
[
(assoc.item.description, assoc.price, assoc.item.price)
for assoc in order.order_items
]
)
# print items based on the "proxied" items collection
print([(item.description, item.price) for item in order.items])
# print customers who bought 'MySQL Crowbar' on sale
orders = (
session.query(Order)
.join("order_items", "item")
.filter(Item.description == "MySQL Crowbar")
.filter(Item.price > OrderItem.price)
)
print([o.customer_name for o in orders])