mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-30 20:44:45 -04:00
Jason Kirtland
177d30cc01
- Deprecated BoundMetaData- use MetaData instead - Removed DMD and BMD from documentation
105 lines
3.0 KiB
Python
105 lines
3.0 KiB
Python
"""basic example of using the association object pattern, which is
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a richer form of a many-to-many relationship."""
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# the model will be an ecommerce example. We will have an
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# Order, which represents a set of Items purchased by a user.
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# each Item has a price. however, the Order must store its own price for
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# each Item, representing the price paid by the user for that particular order, which
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# is independent of the price on each Item (since those can change).
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from sqlalchemy import *
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from sqlalchemy.ext.selectresults import SelectResults
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from datetime import datetime
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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', Float, 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'), primary_key=True),
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Column('item_id', Integer, ForeignKey('items.item_id'), primary_key=True),
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Column('price', Float, 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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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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'items':relation(OrderItem, cascade="all, delete-orphan", lazy=False)
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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.save(Item('SA T-Shirt', 10.99))
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session.save(Item('SA Mug', 6.50))
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session.save(Item('SA Hat', 8.99))
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session.save(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).get_by(description=name)
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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.items.append(OrderItem(item('SA Mug')))
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order.items.append(OrderItem(item('MySQL Crowbar'), 10.99))
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order.items.append(OrderItem(item('SA Hat')))
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session.save(order)
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session.flush()
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session.clear()
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# query the order, print items
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order = session.query(Order).get_by(customer_name='john smith')
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print [(item.item.description, item.price) for item in order.items]
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# print customers who bought 'MySQL Crowbar' on sale
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result = SelectResults(session.query(Order)).join_to('item').select(and_(items.c.description=='MySQL Crowbar', items.c.price>orderitems.c.price))
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print [order.customer_name for order in result]
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