On Tue, Aug 13, 2013 at 2:07 PM, till.plewe <till.pl...@gmail.com> wrote: > I am using python 3.3 and sqlalchemy 0.8.2 > > I am trying to define a self-referential many-to-many relationship for a > class where the primary key is provided by a mixin. Defining the primary > directly in the class works. Using the mixin does not. > > I would be grateful for any suggestions or pointers to relevant > documentation. > > Below is an example showing my problem. As given the example works. > Uncommenting the line "#id = ..." in 'Base' and commenting out the > corresponding line in 'A' breaks the example. Is there any way to define > the primary key in Base and getting the 'requires' relation to work? > > ----------------------------------- > > from sqlalchemy import Column, Integer, String, DateTime, Table, > ForeignKey,create_engine > from sqlalchemy.ext.declarative import declarative_base,declared_attr > from sqlalchemy.orm import sessionmaker, relationship, backref > > class Base(object): > #id = Column(Integer, primary_key=True) > pass > > Base = declarative_base(cls=Base) > > association_table = Table('association', > Base.metadata, > Column('prerequisite', Integer, > ForeignKey('a.id')), > Column('dependency', Integer, ForeignKey('a.id'))) > > class A(Base): > __tablename__ = "a" > id = Column(Integer, primary_key=True) > requires = relationship("A", > secondary = association_table, > > primaryjoin=(id==association_table.c.prerequisite), > > secondaryjoin=(id==association_table.c.dependency), > backref = backref("required_by")) > > if __name__ == "__main__": > engine = create_engine('sqlite:///:memory:', echo=False) > Session = sessionmaker(bind=engine) > session = Session() > Base.metadata.create_all(engine) > > T=A() > U=A() > session.add(T) > session.add(U) > T.requires.append(U) > session.commit() > print("T",T.id,T.requires,T.required_by) > print("U",U.id,U.requires,U.required_by) >
You can make it work by using strings as the primaryjoin and secondaryjoin parameters and referring to A.id rather than just id: class A(Base): __tablename__ = "a" requires = relationship("A", secondary = association_table, primaryjoin="A.id==association.c.prerequisite", secondaryjoin="A.id==association.c.dependency", backref = backref("required_by")) This technique is described in the "Configuring Relationships" section of the declarative documentation: http://docs.sqlalchemy.org/en/rel_0_8/orm/extensions/declarative.html#configuring-relationships Hope that helps, Simon -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/groups/opt_out.