Hi
I'm a Python and SA newbie investigating SA for a project using
Postgres. I have a database schema that I want to point SA at then be
able to write my Python code.
I'm working with a version of the basic_association example to keep
things simple. I want to have unique auto generated ids on my tables
(surrogate primary keys) but also want to have primary keys defined
over the entities' actual attributes. I want to have surrogate keys on
my tables so that I can use them instead of the full priamary keys
when writing joins to keep the SQL brief. In some cases (e.g. the
association table) I'm defining the primary key in terms of surrogate
primary keys rather than copy over the full primary key from the
associated tables.
When I run the code (below) I get AttributeError: 'Order' object has
no attribute '_instance_key'.
Please can someone help me setup SA to work in this example?
Thanks in advance
Phil
Postgress DDL
----------------------
create table orders (
order_id Serial ,
o_customer_name text not null,
o_order_date timestamp not null,
primary key (o_customer_name, o_order_date) using index ,unique
(order_id);
create table items (
item_id Serial ,
it_description text not null,
it_price Numeric(8,2) not null,
primary key (it_description) using index, unique (item_id) using
index);
create table order_items (
oi_order_id Integer not null,
oi_item_id Integer not null,
oi_price Numeric(8,2) not null,
primary key (oi_order_id, oi_item_id) using index);
Python
----------
[SNIP] setup and connect string
engine = create_engine(connectString, echo=False)
metadata = MetaData(engine)
orders_table = Table('orders', metadata, autoload=True)
items_table = Table('items', metadata, autoload=True)
orderitems_table = Table('order_items', metadata,
Column('oi_order_id', Integer,
ForeignKey('orders.order_id'),
primary_key=True),
Column('oi_item_id', Integer,
ForeignKey('items.item_id'),
primary_key=True),
autoload=True
)
class Order(object):
def __init__(self, customer_name, order_date):
self.customer_name = customer_name
self.order_date = order_date
class Item(object):
def __init__(self, description, price):
self.description = description
self.price = price
class OrderItem(object):
def __init__(self, item, price=None):
self.item = item
self.price = price or item.price
mapper(Order, orders_table, properties = {
'id' : orders_table.c.order_id,
'customer_name' : orders_table.c.o_customer_name,
'order_date' : orders_table.c.o_order_date,
'order_items' : relation(OrderItem)
})
mapper(Item, items_table, properties = {
'id' : items_table.c.item_id,
'description' : items_table.c.it_description,
'price' : items_table.c.it_price
})
mapper(OrderItem, orderitems_table, properties = {
'order_id' : orderitems_table.c.oi_order_id,
'item_id' : orderitems_table.c.oi_item_id,
'price' : orderitems_table.c.oi_price,
'item' : relation(Item)
})
Session = sessionmaker(bind=engine, autoflush=True,
transactional=True)
session = Session()
session.save(Item('Item A', 10.99))
session.save(Item('Item B', 8))
session.save(Item('Item C', 4))
session.save(Item('Item D', 1))
session.flush()
def item(name):
return session.query(Item).filter_by(description=name).one()
order = Order("cust1", datetime.now())
order.order_items.append(OrderItem(item('Item A')))
order.order_items.append(OrderItem(item('Item B'),10))
order.order_items.append(OrderItem(item('Item C')))
session.save(order)
session.commit()
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