Michael Chambliss wrote:
Michael Bayer wrote:
On Jan 26, 2010, at 7:48 PM, Michael Chambliss wrote:
Presently, I'm trying to determine the best way to map a class against an
arbitrary select where the select is constructed from raw SQL. Based on this,
it's possible using the expression builders:
http://www.sqlalchemy.org/docs/mappers.html#mapping-a-class-against-arbitrary-selects
from_statement() is the primary means of doing this, assuming you're mapped to
some kind of construct already and just need to select the rows from some
particular statement you happen to have as a string. This means, the
configuration of your application would consist of mapping your classes to
table metadata as per the documentation, and then at query time you can load
and persist objects, using all hand-written SQL to load rows.
In a theoretical example, say I have a CAR table that refers to both a
CAR_TYPE table and CAR_ATTRIBUTES table. CAR_TYPE is simply an
enumeration for a static list of types, and CAR_ATTRIBUTES is an
arbitrarily long list of key,value attributes (color, weight, top
speed, etc). So, ultimately, a "Car" is made up of these three.
I'd want to bake all of these together, passing in a CAR.ID (primary
key) to map to a Car instance.
Michael - this may better illustrate the question. Note the ??query??.
engine = create_engine('oracle://user:passw...@server:1521/database')
Session = sessionmaker(bind=engine)
s = Session()
metadata = MetaData()
vehicle_query = """
select
v.vehicle_id as vehicle_id,
v.name as vehicle_name,
v.description as vehicle_description,
vt.name as vehicle_type,
vs.name as vehicle_status,
v.modify_dttm as vehicle_modify_dttm
from
vehicle v,
vehicle_type vt,
vehicle_status vs
where
v.vehicle_id = :vehicle_id
and vs.vehicle_status_id = v.vehicle_status_id
and vt.vehicle_type_id = v.vehicle_type_id
"""
class Vehicle(object):
def __init__(self, vehicle_id, vehicle_name, vehicle_description,
vehicle_type, vehicle_status, vehicle_modify_dttm):
self.vehicle_id = vehicle_id
self.vehicle_name = vehicle_name
self.vehicle_description = vehicle_description
self.vehicle_type = vehicle_type
self.vehicle_status = vehicle_status,
self.vehicle_modify_dttm = vehicle_modify_dttm
def __repr__(self):
return "<Name('%s')>" % (self.vehicle_name)
# Here's where I get sideways...
# Obviously this won't work, but I'm not sure how to map the query to
the class
mapper(Vehicle, ??query??)
metadata.bind = engine
q = s.query(Vehicle).from_statement(vehicle_query).params(vehicle_id=123)
for vehicle in q:
print vehicle.vehicle_id, vehicle.vehicle_name
#...
Thanks,
Mike
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