On May 20, 2010, at 10:20 AM, bogun.dmit...@gmail.com wrote: > Hello. > > Is there any way I can use some expression for polymorphic_on mapper > attribute?
You can get this behavior now with some effort if you create a SELECT statement that loads the full row, including your "discriminator", and set it as "with_polymorphic". There's some examples for this in http://www.sqlalchemy.org/docs/mappers.html#concrete-table-inheritance . Allowing "polymorphic_on" to just be a plain function, which would be eaiser, is a TODO, there's tickets in trac to address this feature eventually. > > I have tried some ways, but not got what I want. > > # --- my tries > import sqlalchemy as sa > from sqlalchemy import * > from sqlalchemy import orm > from sqlalchemy.ext.declarative import declarative_base > > _decl = declarative_base() > > class generic(_decl): > __tablename__ = 'generic' > > idnr = Column(Integer, primary_key=True) > type = Column(String(32), nullable=False) > data = Column(String(128)) > discriminator = orm.column_property(case(value=type, whens={'abc':type, > 'cde':type}, else_='generic').label('discriminator')) > > __mapper_args__ = {'polymorphic_on': type, > 'polymorphic_identity':'generic'} > #__mapper_args__ = {'polymorphic_on': discriminator, > 'polymorphic_identity':'generic'} > #__mapper_args__ = {'polymorphic_on': case(value=type, whens={'abc':type, > 'cde':type}, else_='generic'), 'polymorphic_identity':'generic'} > > class type_abc(generic): > __tablename__ = 'abc' > > generic_idnr = Column(Integer, ForeignKey(generic.idnr, > onupdate='CASCADE', ondelete='CASCADE'), primary_key=True) > abc = Column(Integer, nullable=False) > __mapper_args__ = {'polymorphic_identity':'abc'} > > class type_cde(generic): > __tablename__ = 'cde' > > generic_idnr = Column(Integer, ForeignKey(generic.idnr, > onupdate='CASCADE', ondelete='CASCADE'), primary_key=True) > cde = Column(Integer, nullable=False) > __mapper_args__ = {'polymorphic_identity':'cde'} > > def main(): > engine = create_engine('sqlite:///:memory:', echo=True) > generic.metadata.create_all(engine) > sm = orm.sessionmaker(bind=engine) > ses = sm() > > a = type_cde() > a.cde = 1 > ses.add(a) > > a = type_abc() > a.abc = 2 > ses.add(a) > > #pdb.set_trace() > a = generic() > a.type = 'zzz' > a.data = 'a vot tak?' > ses.add(a) > > ses.commit() > > if __name__ == '__main__': > main() > # ---- code end > > It works only with real column instance... > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalch...@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. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@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.
