Awesome, thank you much. It is correlated to the parent. The query- enabled properties section looks interesting to me. Will there be a significant performance difference between the two approaches? I want this to be lazily evaluated, so that this information is never fetched unless we actually request that attribute.
On Mar 16, 3:44 pm, Michael Bayer <mike...@zzzcomputing.com> wrote: > this kind of pattern is usually handled by column_property(), assuming you > can correlate your subquery to the parent within the WHERE clause such that > the return value is a scalar. > > Below if you really just wanted "the first row" you'd want to say "limit(1)". > If you really want that exact same first row of the table every time, it > would be better as just an additional method or descriptor on your OrderChain > object, (or even if not) perhaps even as a class method if the value truly > has no correlation to the identity of the parent (which seems unlikely). > > Two different strategies at: > > http://www.sqlalchemy.org/docs/orm/mapper_config.html#sql-expressions... > > http://www.sqlalchemy.org/docs/orm/relationships.html#building-query-...- > specific to relationship(), but the same idea could be applied to columns too. > > On Mar 16, 2011, at 10:23 AM, hoesley wrote: > > > > > > > > > I am trying to create a property on a mapped class which basically > > executes a subquery. Here is what I'm trying to do in non-working > > pseudo code: > > > mapper(OrderChain, Table('order_chains', self.meta, > > autoload=True), > > properties={'entries': relation(OrderChainEntry, > > order_by=Column('timestamp')), > > 'first_cancel': > > select(OrderChainEntry).filter('type'='new').first() > > }) > > > Is something like this possible? Or what's the best way to approach > > it? > > > Also, if I've mangled terminology and/or written something that makes > > no sense, please let me know - I'm very new to this package! > > > Cheers, > > Andrew > > > -- > > You received this message because you are subscribed to the Google Groups > > "sqlalchemy" group. > > To post to this group, send email to sqlalchemy@googlegroups.com. > > To unsubscribe from this group, send email to > > sqlalchemy+unsubscr...@googlegroups.com. > > For more options, visit this group > > athttp://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
