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BOBOTANG
114 lines
3.3 KiB
Python
114 lines
3.3 KiB
Python
"""Illustrate a many-to-many relationship between an
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"Order" and a collection of "Item" objects, associating a purchase price
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with each via an association object called "OrderItem"
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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 and_
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from sqlalchemy import Column
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from sqlalchemy import create_engine
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from sqlalchemy import DateTime
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from sqlalchemy import Float
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from sqlalchemy import ForeignKey
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from sqlalchemy import Integer
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from sqlalchemy import String
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from sqlalchemy.ext.declarative import declarative_base
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from sqlalchemy.orm import relationship
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from sqlalchemy.orm import Session
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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(
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"OrderItem", cascade="all, delete-orphan", backref="order"
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)
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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)" % (self.description, self.price)
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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(
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[
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(order_item.item.description, order_item.price)
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for order_item in order.order_items
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]
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)
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# print customers who bought 'MySQL Crowbar' on sale
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q = session.query(Order).join(OrderItem).join(Item)
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q = q.filter(
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and_(Item.description == "MySQL Crowbar", Item.price > OrderItem.price)
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)
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print([order.customer_name for order in q])
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