Hello,
Today I have questions regarding generic associations and more specifically the *table_per_association* example: http://docs.sqlalchemy.org/en/latest/_modules/examples/generic_associations/table_per_association.html I am trying to adapt it to the following case: - A class *Object* which represents objects in the game (like potions or weapons) - A class *ObjectContainer* which represents a container with a list of objects contained in it (a chest for example) - A class *Hands* which represents the hands of a player. These hands can hold objects. However, the class Hands must not directly contain the list of the objects held by the players. The class Hands finds them in another way Here is my code: from sqlalchemy.ext.declarative import as_declarative, declared_attr from sqlalchemy import create_engine, Integer, Column, \ String, ForeignKey, Table from sqlalchemy.orm import Session, relationship @as_declarative() class Base(object): """Base class which provides automated table name and surrogate primary key column. """ @declared_attr def __tablename__(cls): return cls.__name__.lower() id = Column(Integer, primary_key=True) class Object(Base): name = Column(String, nullable=False) class HasObjects(object): @declared_attr def objects(cls): object_association = Table( "%s_objects" % cls.__tablename__, cls.metadata, Column("object_id", ForeignKey("object.id"), primary_key=True), Column("%s_id" % cls.__tablename__, ForeignKey("%s.id" % cls.__tablename__), primary_key=True), ) return relationship(Object, secondary=object_association) # The following line doesn't works : # # return relationship(Object, secondary=object_association, backref="parent") # # Error : # # sqlalchemy.exc.ArgumentError: Error creating backref 'parent' on # relationship 'ObjectContainer.objects': property of that name exists on mapper # 'Mapper|Object|object' class ObjectContainer(HasObjects, Base): name = Column(String) class Hands(HasObjects, Base): name = Column(String) engine = create_engine('sqlite://', echo=True) Base.metadata.create_all(engine) session = Session(engine) session.add_all([ ObjectContainer( name='Chest 1', objects=[ Object(name="potion 1"), Object(name="potion 2") ] ), Hands( name="Hands player 1", objects=[ Object(name="potion 3"), Object(name="potion 4") ] ), ]) session.commit() I have two questions: 1. How could I have a parent attribute in *Object* linked to *ObjectContainer* or *Hands*? I tried with backref but it doesn’t seems to work (see comments in the code) 2. How could I avoid the fact that *Hands*, with this *HasObjects* mixin, automatically get a list of objects? I only need to have the parent attribute of *Object* linked to *Hands* but I don’t need to have any list of the objects in *Hands*. Of course, I could ignore that and let the list be created but it’s a bit dirty I assume that the answers are pretty simple but I think my comprehension of the “secondary” parameter of relationship is not good enough to find a solution. Thank you! Sven -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- 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 https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
