OK I think that would work for me. I have another question in regards to joined table inheritance and performance. At work we are planning to restructure our database schema, and what we are considering doing is creating an adjacency list, of objects using joined table inheritance. We are thinking there would be at least four subtypes, where each would be a subclass of the previous (B inherits from A, and C inherits from B). We are doing it this way because every object could overload a value from its parent (probably won't 90% of the time). We would probably want to eagerly load children two levels deep, and at the lowest level an object would make up a join of four tables.
The table will be populated with the rows from two existing tables one with 11,000 rows the other with 40,000 rows, so presumably in the near future the table would have well over 100,000 rows. How bad do you think the performance would be? Is this something that is just too crazy to try? Michael Bayer wrote: > mmmm yeah. OK we only have limited support for that concept right now > using of_type(), which currently only supports one type, not a list. > so it would be > query(Company).join(Company.employees.of_type(Engineer)). In theory > of_type() could support a list, but that isnt built right now. So to > really get the full SQL you're looking for you'd have to go "old > school" and use the table objects here, like: > > session > .query > (Company > ).select_from > (company_table.join(employees_table).outerjoin(engineers_table, > <onclause>).outerjoin(managers_table, <onclause>)).<everything else>. > > you'll actually get a better query from the above since it won't wrap > the engineer/manager stuff in a subquery. > > > > On Jun 10, 2009, at 8:38 PM, David Gardner wrote: > > >> I was wondering if there was a way to use with_polymorphic() on a >> joined >> table. >> >> For instance using the Company->Employees relationship in the >> example on >> http://www.sqlalchemy.org/docs/05/mappers.html#mapping-class-inheritance-hierarchies >> >> if I wanted to query for a company, and eagerload the employees and >> eagerly join the engineers and managers tables I would think to do >> something like: >> >> session.query(Company).join(Company.employees).\ >> options(contains_eager(Company.employees)).\ >> with_polymorphic([Engineer, Manager]).\ >> filter(Company.name=='test').first() >> >> >> >> -- David Gardner Pipeline Tools Programmer Jim Henson Creature Shop dgard...@creatureshop.com --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
