On Aug 26, 2011, at 9:36 PM, Michael Bayer wrote:
> 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.
Oops, that sounds plausible. I guess I was tacitly assuming that
SQLalchemy would somehow abstract away from the association
object and let me create relations between the Objects directly (but then how
would I define
the extra attributes of the association?).
Thanks!
>
>
>
> On Aug 26, 2:53 pm, Thomas Jacob <[email protected]> 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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