Excerpts from gsandorx's message of Tue Dec 22 16:03:44 -0300 2009:
> Hi Mariano, I tried your code and it worked great. Now I have to look
> a way of linking the "union" query with a mapper to obtain a rather
> elaborate object than a raw tuple, I mean, when you execute:
> q = session.query(Computer).all()
> you get Computer objects, but when you execute the "union" query you
> get tuples.
Although they look like tuples, they're actually
RowProxies and they provide some useful methods for solving this kind of
situations.
For more on RowProxy, please see [1]
> When looking at the resulting tuples, I noticed that those tuples that
> represent Computer objects contains a field equal to "None" due to the
> extra column added in the query. I guess that field could be used
> somehow to distinguish between Computer-like tuples and
> CompSetComputer-like ones.
I used a null value just a convenience to show the possible solution.
Actually you could use whatever you want in there: the bottom problem
was that you cannot union two queries with different quantities of
columns.
> I'm telling you this b/c I would like to
> know if there is a mechanism to link a method to a mapper. This way,
> the method would process the "union" query, and would create a list of
> Computer and CompSetComputer objects. Do I make myself clear?
> Thanks for your help,
> Sandor
>
Off the top of my head, I could suggest a factory to build the objects.
This example, of course, has nothing to do with the ORM.
Maybe more tech savy guys can suggest better options.
For example:
class UnionComputers(object):
"""You can extend this class with whatever methods you
would like"""
def __init__(self, **kwargs):
for every in kwargs.items():
setattr(self, every[0], every[1])
class UnionFactory(object):
"""Factory is maybe too big of a name since we're building just
one type of object"""
@staticmethod
def return_inst(l_inst):
for every in l_inst:
yield UnionComputers(**dict([(str(x[0]), x[1]) for x in
every.items()]))
factory = UnionFactory()
gen = factory.return_inst(session.execute(q3).fetchall())
while 1:
v = gen.next()
print(type(v), v.ip)
[1]
http://www.sqlalchemy.org/docs/05/reference/sqlalchemy/connections.html#sqlalchemy.engine.base.RowProxy
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