seems like "SELECT * from parent WHERE type='child1'" should do it there. If you were to say sess.query(Child1).all() it would do a JOIN to limit the results, if you want to go that route you'd say "SELECT * from parent JOIN child1 ON parent.id=child1.id".
So to answer your question, with the configuration given, there's no way for the polymorphic load to return only Child1 objects if the corresponding SQL is returning other kinds of rows. As an alternative you can create a non-primary mapper that is only against "parent join child1" (i.e. mapper(Child1, parent.join(child1), non_primary=True) ) and query using that mapper - but that will still interpret rows which correspond to Parent or Child2 objects as Child1 objects, which is "incorrect" by most standards. If OTOH you really want just the rows that have "child1" as a type, and for some reason you can't establish that criteria in the SQL, then you'd need to filter the results after the fact. though I can't imagine a scenario where an existing SQL statement is present that cannot have a simple "WHERE type='child1'" added to it. On Oct 27, 2008, at 2:01 PM, Matthias wrote: > > On 27 Okt., 17:36, Michael Bayer <[EMAIL PROTECTED]> wrote: >> On Oct 27, 2008, at 12:19 PM, Matthias wrote: >> >> >> >> >> >>> Hi, >>> i have a problem regarding inheritance. I use joined table >>> inheritance. Assume the classes parent, child1 and child2. The >>> parent_table has a field 'type'. I have to use >>> 'session.query(child1).from_statement(deliver_me_parents_with >>> special_conditions).all()' - the result contains child1 and child2 >>> objects. The documentation says sth. about bypassing all other >>> stuff, >>> but my description was just a model for my problem, i can not do >>> anything like "type=child1" in the statment, cause there is a deeper >>> inheritance structure. >> >>> Summary: I have a result set of 'parents' but i want to get only the >>> child1 objects. The result of 'from_statement' contains the type- >>> column, so SQLAlchemy should be able to resolve the child1 objects? >> >> it should. is child2 a subclass of child1 ? > > The answer to your question is sometimes yes and sometimes no. > I created a small example which illustrates my problems. Please keep > in mind that the 'from_statement' part is just a placeholder for > something which can not be replaced by anything. > If this can not be done the way i am trying at the moment, please give > me a hint for a solution where i do not have to find out the mapper/ > class or table name. > > I need something like > 'session.query(AnyChildClass).from_statement(stmt).all()' and it > should deliver only objects of type 'AnyChildClass.'. > > SQLAlchemy version: SQLAlchemy 0.4.8 > > My example for this topic: > ------------------------------------- > > # -*- coding: utf-8 -*- > > """ > Small inheritance example for SQLAlchemy mailing list. > @see: > http://groups.google.com/group/sqlalchemy/browse_thread/thread/1df94a3d59105688?hl=de > """ > > from sqlalchemy import * > from sqlalchemy.orm import mapper, sessionmaker > > # create engine, metadata and session > engine = create_engine('postgres://[EMAIL PROTECTED]/inheritance') > metadata = MetaData() > metadata.bind = engine > Session = sessionmaker(bind=engine) > session = Session() > > # table definitions > parent_table = Table("parent", metadata, > Column("id", Integer, primary_key=True), > Column("type", String(30), nullable=False)) > > child1_table = Table("child1", metadata, > Column("id", Integer, ForeignKey("parent.id"), primary_key=True)) > > child2_table = Table("child2", metadata, > Column("id", Integer, ForeignKey("parent.id"), primary_key=True)) > > # class definitions > class Parent(object): > def __repr__(self): > return "%-10s, id: %s" %(self.__class__.__name__, self.id) > > class Child1(Parent): > pass > > class Child2(Parent): > pass > > # mapper definitions > mapper(Parent, parent_table, polymorphic_on=parent_table.c.type, \ > polymorphic_identity='parent') > > mapper(Child1, child1_table, inherits=Parent, \ > polymorphic_identity='child1') > > mapper(Child2, child2_table, inherits=Parent, \ > polymorphic_identity='child2') > > > # create db tables > metadata.create_all() > > # create some objects and commit them to the db > p = Parent() > c1 = Child1() > c2 = Child2() > > for obj in [p,c1,c2]: > session.save(obj) > session.flush() > session.commit() > > # try to get only objects of Type 'Child1' > stmt = "SELECT * FROM parent" > result = session.query(Child1).from_statement(stmt).all() > > # will print: (how can i solve this?) > # Parent , id: 1 > # Child1 , id: 2 > # Child2 , id: 3 > for obj in result: > print obj > > --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
