mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-13 12:17:28 -04:00
Michael Trier
6010afb28f
Explicit imports make it easier for users to understand the examples. Additionally a lot of the examples were fixed to work with the changes in the 0.5.x code base. One small correction to the Case expression. Thanks a bunch to Adam Lowry! Fixes #717.
109 lines
3.5 KiB
Python
109 lines
3.5 KiB
Python
"""A basic example of using the association object pattern.
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The association object pattern is a richer form of a many-to-many
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relationship.
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The model will be an ecommerce example. We will have an Order, which
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represents a set of Items purchased by a user. Each Item has a price.
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However, the Order must store its own price for each Item, representing
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the price paid by the user for that particular order, which is independent
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of the price on each Item (since those can change).
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"""
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from datetime import datetime
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from sqlalchemy import (create_engine, MetaData, Table, Column, Integer,
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String, DateTime, Numeric, ForeignKey, and_)
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from sqlalchemy.orm import mapper, relation, create_session
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# Uncomment these to watch database activity.
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#import logging
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#logging.basicConfig(format='%(message)s')
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#logging.getLogger('sqlalchemy.engine').setLevel(logging.INFO)
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engine = create_engine('sqlite:///')
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metadata = MetaData(engine)
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orders = Table('orders', metadata,
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Column('order_id', Integer, primary_key=True),
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Column('customer_name', String(30), nullable=False),
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Column('order_date', DateTime, nullable=False, default=datetime.now()),
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)
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items = Table('items', metadata,
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Column('item_id', Integer, primary_key=True),
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Column('description', String(30), nullable=False),
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Column('price', Numeric(8, 2), nullable=False)
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)
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orderitems = Table('orderitems', metadata,
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Column('order_id', Integer, ForeignKey('orders.order_id'),
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primary_key=True),
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Column('item_id', Integer, ForeignKey('items.item_id'),
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primary_key=True),
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Column('price', Numeric(8, 2), nullable=False)
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)
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metadata.create_all()
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class Order(object):
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def __init__(self, customer_name):
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self.customer_name = customer_name
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class Item(object):
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def __init__(self, description, price):
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self.description = description
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self.price = price
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def __repr__(self):
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return 'Item(%s, %s)' % (repr(self.description), repr(self.price))
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class OrderItem(object):
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def __init__(self, item, price=None):
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self.item = item
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self.price = price or item.price
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mapper(Order, orders, properties={
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'order_items': relation(OrderItem, cascade="all, delete-orphan",
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backref='order')
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})
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mapper(Item, items)
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mapper(OrderItem, orderitems, properties={
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'item': relation(Item, lazy=False)
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})
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session = create_session()
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# create our catalog
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session.add(Item('SA T-Shirt', 10.99))
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session.add(Item('SA Mug', 6.50))
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session.add(Item('SA Hat', 8.99))
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session.add(Item('MySQL Crowbar', 16.99))
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session.flush()
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# function to return items from the DB
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def item(name):
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return session.query(Item).filter_by(description=name).one()
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# create an order
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order = Order('john smith')
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# add three OrderItem associations to the Order and save
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order.order_items.append(OrderItem(item('SA Mug')))
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order.order_items.append(OrderItem(item('MySQL Crowbar'), 10.99))
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order.order_items.append(OrderItem(item('SA Hat')))
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session.add(order)
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session.flush()
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session.expunge_all()
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# query the order, print items
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order = session.query(Order).filter_by(customer_name='john smith').one()
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print [(order_item.item.description, order_item.price)
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for order_item in order.order_items]
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# print customers who bought 'MySQL Crowbar' on sale
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q = session.query(Order).join(['order_items', 'item'])
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q = q.filter(and_(Item.description == 'MySQL Crowbar',
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Item.price > OrderItem.price))
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print [order.customer_name for order in q]
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