the error message here isn't fantastic but I think you mean to say:
oa = ObjectAssociation()
o2.relate_down.append(oa)
o.relate_up.append(oa)
as relate_up/relate_down accept ObjectAssociation objects, not Object
objects, as members.
On Aug 26, 2:53 pm, Thomas Jacob <ja...@internet24.de> wrote:
> Hello List
>
> I'd like to define a many-to-many relationship using the declarative
> syntax between a table to itself, but employing an association
> object (since I require the association to have attributes
> also).
>
> Here's what I tried:
>
> #=================================================================
>
> from sqlalchemy import *
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import sessionmaker, relation, backref
>
> DB_engine = create_engine('sqlite:///:memory:', echo=True)
> DB_Base = declarative_base(bind=DB_engine)
> DB_Session = sessionmaker()
> DB_Session.configure(bind=DB_engine)
> DB_session = DB_Session()
>
> class Object(DB_Base):
> __tablename__ = 'object'
>
> object_id = Column(Integer, primary_key=True)
> label = Column(Text)
>
> class ObjectAssociation(DB_Base):
> __tablename__ = 'object_association'
> __table_args__ = (
> PrimaryKeyConstraint('left_object_id', 'right_object_id'),
> {}
> )
>
> left_object_id = Column(Integer, ForeignKey('object.object_id'))
> right_object_id = Column(Integer, ForeignKey('object.object_id'))
> label = Column(Text)
>
> left_object = relation(Object,
> primaryjoin=(left_object_id==Object.object_id),
> backref=backref("relate_down")
> )
> right_object = relation(Object,
> primaryjoin=(right_object_id==Object.object_id),
> backref=backref("relate_up")
> )
>
> DB_Base.metadata.create_all()
>
> o = Object()
> o.label = 'Object1'
>
> o2 = Object()
> o2.label = 'Object2'
>
> o2.relate_down.append(o)
>
> DB_session.commit()
>
> #=================================================================
>
> But this raises an exception:
>
> #=================================================================
>
> 2011-08-26 20:48:28,422 INFO sqlalchemy.engine.base.Engine PRAGMA
> table_info("object")
> 2011-08-26 20:48:28,422 INFO sqlalchemy.engine.base.Engine ()
> 2011-08-26 20:48:28,422 INFO sqlalchemy.engine.base.Engine PRAGMA
> table_info("object_association")
> 2011-08-26 20:48:28,422 INFO sqlalchemy.engine.base.Engine ()
> 2011-08-26 20:48:28,423 INFO sqlalchemy.engine.base.Engine
> CREATE TABLE object (
> object_id INTEGER NOT NULL,
> label TEXT,
> PRIMARY KEY (object_id)
> )
>
> 2011-08-26 20:48:28,423 INFO sqlalchemy.engine.base.Engine ()
> 2011-08-26 20:48:28,423 INFO sqlalchemy.engine.base.Engine COMMIT
> 2011-08-26 20:48:28,423 INFO sqlalchemy.engine.base.Engine
> CREATE TABLE object_association (
> left_object_id INTEGER,
> right_object_id INTEGER,
> label TEXT,
> PRIMARY KEY (left_object_id, right_object_id),
> FOREIGN KEY(left_object_id) REFERENCES object (object_id),
> FOREIGN KEY(right_object_id) REFERENCES object (object_id)
> )
>
> 2011-08-26 20:48:28,423 INFO sqlalchemy.engine.base.Engine ()
> 2011-08-26 20:48:28,424 INFO sqlalchemy.engine.base.Engine COMMIT
> Traceback (most recent call last):
> File "bug.py", line 53, in <module>
> o2.relate_down.append(o)
> File
> "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/collections.py",
> line 952, in append
> item = __set(self, item, _sa_initiator)
> File
> "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/collections.py",
> line 927, in __set
> item = getattr(executor, 'fire_append_event')(item, _sa_initiator)
> File
> "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/collections.py",
> line 618, in fire_append_event
> item, initiator)
> File
> "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/attributes.py",
> line 745, in fire_append_event
> value = fn(state, value, initiator or self)
> File
> "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/attributes.py",
> line 943, in emit_backref_from_collection_append_event
> child_state.manager[key].impl.append(
> KeyError: 'left_object'
>
> #===================================================================
>
> Is this a bug? Am I doing something wrong?
>
> Any clue as to what is going on here would be greatly appreciated.
>
> The platform I ran this on was Ubuntu 10.04's Python 2.6.5 + SQLAlchemy
> 0.7.2.
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