As with the general questions that come up around .select() and joins, the
underlying issue is the expectation that "instances of a SQLObject-derived class
are returned". So in your work here, the main bit is creating a fake class that
is "enough" like a SQLObject.
Also in trunk (views.py) is an alternate approach I took, ViewSQLObject:
"""
A SQLObject class that derives all it's values from other SQLObject classes.
Columns on subclasses should use SQLBuilder constructs for dbName, and
sqlmeta should specify:
* idName as a SQLBuilder construction
* clause as SQLBuilder clause for specifying join conditions or other
restrictions
* table as an optional alternate name for the class alias
See test_views.py for simple examples.
"""
In many ways it's no prettier a hack than your efforts, but here's what it would
look like using it for the problem in the other active thread on this topic (Jim
Steil):
class RailCarWithStatus(ViewSQLObject):
class sqlmeta:
idName = RailCar.q.id
clause = RailCar.q.id==RailStatus.q.railCarID
carInitials = StringCol(dbName=RailCar.q.carInitials)
# ... other RailCar columns to pull in
status = StringCol(dbName=RailStatus.q.status)
# ... other RailStatus columns to pull in
and then you'd just do RailCarWithStatus.select(...)
It's still rough, I'm not directly advocating its use yet (I don't believe it
supports SQLBuilder JOIN syntaxes so outer joins are currently out, for
instance, although it would be easy to add. Same with groupBy etc - as the api
currently stands, presumably most of the optional arguments to Select would end
up in sqlmeta to support these things). The motivation when writing it was to
define aggregate columns to be retrieved with instance loading, so there's a lot
of work in generating "safe" nested aliased select statements - it's been tested
on PostgreSQL & SQLite as I recall.
The clear alternative approach would be along your lines, emphasizing
SQLBuilder/SelectResults and loosening the ties to SQLObjects so that it's
easier to substitute other classes to be returned. In a lot of ways I like that
direction, let me refresh my memory on the guts of this code and see what else
I'd do with your approach.
- Luke
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