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This is from my blog post on pynash.org on 2013-03-01
from sqlalchemy import create_engine
engine = create_engine('sqlite:///:memory', echo=True)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.hybrid import hybrid_property
Base = declarative_base()
from sqlalchemy import Column, Integer, String, Float
class Order(Base):
__tablename__ = 'orders'
order_id = Column(Integer, primary_key=True)
order_reference_code = Column(String)
merchandise_cost = Column(Float)
tax = Column(Float)
shipping = Column(Float)
def __init__(self, order_reference_code, merchandise_cost, tax, shipping):
self.order_reference_code = order_reference_code
self.merchandise_cost = merchandise_cost
self.tax = tax
self.shipping = shipping
@hybrid_property
def grand_total(self):
rollup_fields = [
'merchandise_cost',
'tax',
'shipping',
]
total = sum([self.__getattribute__(x) for x in rollup_fields])
return round(total, 2)
Base.metadata.create_all(engine)
order1 = Order('ABC', 57.50, 11.75, 6.00)
order2 = Order('BCD', 21.42, 4.72, 3.00)
order3 = Order('CDE', 1000.50, 80.34, 0.00)
order4 = Order('DEF', 500.50, 45.34, 100.00)
from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
db = Session()
db.add(order1)
db.add(order1)
db.add(order1)
db.add(order1)
db.commit()
for order in db.query(Order).all():
print order.order_reference_code, order.grand_total
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