polymorphic_identity is intended to link to the "class" of an entity in a one-to-one fashion, so using a date type for this column would not be an appropriate usage. We have eventual plans to support polymorphic_identity supplied by a function but that feature is currently not implemented.
You might consider looking into MapperExtension.create_instance() for this use case. On Feb 5, 2009, at 10:24 AM, Toby Bradshaw wrote: > > Hi, > > So I (think I) understand that that polymorphic_on and > polymorphic_identity can be used to determine which class is > instantiated for a query result row. Is there any way I can use a > range > of values for polymorphic_identity to map to the same class ? Of > specific interest to me right now are date ranges and single-table > inheritance. > > e.g. I have two classes: Employee and CurrentEmployee. Both are mapped > to the same table, employee, but Employee.query() should return every > record in the table and CurrentEmployee() should return the same > subset > as Employee.query(Employee.start_date >= today), for example. > > It really is just a convenience thing so not a show stopper but > would be > nice to know if this kind of thing is straightforwardly possible. > > -- > t o b e > -- > A truly clever developer will create code so easy to understand that > a less than average developer could debug it. > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
