Yes, if this has been defined on the mapper. Generally I do a lot of
just using SQLAlchemy to as a way of writing SQL in Python code that
can be passed around for dynamically building up queries so my mappers
tend to be quite bare - or are you suggesting this can be done without
configuring the relation on the mapper ? If there's a way to do this
in SQLAlchemy that doesn't need extra mapper config then I'm all
ears. :-)
On Mar 31, 3:22 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
> wouldn't this be accomplished more simply using contains_eager() ?
>
> On Mar 31, 2009, at 9:12 AM, Bob Farrell wrote:
>
>
>
> > Hello, SQLAlchemy people,
>
> > So I spoke to jek on IRC to see if there was a way to use add_column
> > without causing the query to return a RowTuple and it doesn't look
> > like there is, so I wrote this:
>
> > class AdditiveQuery(Query):
> > """
> > Extended sqlalchemy.orm.Query class with add_named_column method
> > to add a
> > column onto a query but store the values on the main RowProxy
> > object
> > instead of yielding RowTuples as add_column does:
>
> > q = AdditiveQuery(FooModel, session=some_session)
> > q = q.join((BarModel, FooModel.x == BarModel.x))
> > q = q.add_named_column(BarModel.baz, 'bar_baz')
> > for row in q:
> > print q.bar_baz
> > """
> > def __init__(self, *args, **kwargs):
> > self._named_columns = []
> > super(AdditiveQuery, self).__init__(*args, **kwargs)
>
> > def add_named_column(self, column, alias=None):
> > if alias is None:
> > alias = column.key
> > if alias in self._named_columns:
> > raise ValueError("Alias <%s> already in use." % (alias,))
> > self._named_columns.append(alias)
> > return self.add_column(column)
>
> > def __iter__(self):
> > def g(it):
> > checked = False
> > for rows in it:
> > row = rows[0]
> > rest = rows[1:]
> > for alias, value in zip(self._named_columns, rest):
> > if not checked and hasattr(row, alias):
> > raise ValueError("Alias <%s> already exists on
> > "
> > "original row object." % (alias,))
> > setattr(row, alias, value)
> > yield row
> > checked = True
> > it = super(AdditiveQuery, self).__iter__()
> > return g(it)
>
> > The only immediate issue I can think of with this is that if you do
> > AdditiveQuery(FooModel, BarModel) then this is going to blow up as
> > it'll try to call setattr on a RowTuple - I'm not sure whether to a)
> > just let this happen, b) take preventative measures and raise a more
> > useful exception, c) allow specifying exactly which entity to attach
> > the named_column onto.
>
> > Any suggestions welcome and, of course, if any of the SA boys want to
> > stick this into SQLAlchemy, you're more than welcome.
>
> > Thanks !
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