On Nov 1, 2009, at 8:10 PM, Ghost wrote:
> How does one go about doing that? If you need to use the orm to query > the database for columns that do not exist in the table itself, do you > not need to add these to the mapper? Can that be done without > synonyms? if "do not exist in the table itself", you mean you'd like an attribute that represents some concept, such as a string concatenation like "first_name || ' ' || last_name", the column_property() construct is used for that. that basic idea is illustrated at http://www.sqlalchemy.org/docs/05/mappers.html#sql-expressions-as-mapped-attributes . You can also customize further if you'd like to optimize the kinds of expressions the attribute generates when querying - the entrypoint to those techniques are at http://www.sqlalchemy.org/docs/05/mappers.html#custom-comparators . > > I have thought of a sensical example to illustrate what I am trying to > do: You want a field for the age of a person even though you only > store their date of birth in the database table. You want to be able > to query the database by filtering using the age column so I assume > you need to add it to the mapper. > > Should it be done in the following way or is another approach > favoured? your best bet would be to identiify the SQL expression that best suits your needs and use column_property(). Doing the work on the SQL side allows the concept to be used as a filtering/ordering criterion on the database side. > > === > class Person(object): > def _set_age(self, value): > pass > def _get_age(self): > return date.today() - self.date_of_birth > age = property(_get_age, _set_age) > > mapper(Person, person_table, properties={ > 'age': synonym("date_of_birth") > }) > === > > Thank you for your help.. > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
