mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-10 02:39:59 -04:00
Mike Bayer
8af45f93cb
to use declarative, added a new example dict_of_sets_with_default.py, a "pushing the envelope" example of association proxy.
95 lines
3.0 KiB
Python
95 lines
3.0 KiB
Python
"""A basic example of using the association object pattern.
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The association object pattern is a form of many-to-many which
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associates additional data with each association between parent/child.
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The example illustrates an "order", referencing a collection
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of "items", with a particular price paid associated with each "item".
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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, Float, ForeignKey, and_)
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from sqlalchemy.orm import mapper, relationship, Session
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from sqlalchemy.ext.declarative import declarative_base
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Base = declarative_base()
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class Order(Base):
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__tablename__ = 'order'
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order_id = Column(Integer, primary_key=True)
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customer_name = Column(String(30), nullable=False)
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order_date = Column(DateTime, nullable=False, default=datetime.now())
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order_items = relationship("OrderItem", cascade="all, delete-orphan",
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backref='order')
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def __init__(self, customer_name):
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self.customer_name = customer_name
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class Item(Base):
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__tablename__ = 'item'
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item_id = Column(Integer, primary_key=True)
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description = Column(String(30), nullable=False)
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price = Column(Float, nullable=False)
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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(%r, %r)' % (
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self.description, self.price
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)
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class OrderItem(Base):
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__tablename__ = 'orderitem'
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order_id = Column(Integer, ForeignKey('order.order_id'), primary_key=True)
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item_id = Column(Integer, ForeignKey('item.item_id'), primary_key=True)
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price = Column(Float, nullable=False)
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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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item = relationship(Item, lazy='joined')
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if __name__ == '__main__':
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engine = create_engine('sqlite://')
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Base.metadata.create_all(engine)
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session = Session(engine)
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# create catalog
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tshirt, mug, hat, crowbar = (
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Item('SA T-Shirt', 10.99),
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Item('SA Mug', 6.50),
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Item('SA Hat', 8.99),
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Item('MySQL Crowbar', 16.99)
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)
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session.add_all([tshirt, mug, hat, crowbar])
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session.commit()
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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(mug))
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order.order_items.append(OrderItem(crowbar, 10.99))
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order.order_items.append(OrderItem(hat))
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session.add(order)
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session.commit()
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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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