the (child.c.current_id ==child.c.id) part of the "parent" relation is
the culprit here, and also its nonsensical. the relation between
parent and child is strictly based on the FK between those two
tables. additionally its by definition a many-to-one relation; there
is only one possible Parent that can be attached to the Child so even
if the additional criterion *did* make sense, its still wouldnt affect
the outcome.
Ill look into clarifying sqlalchemy's behavior with regards to the
error message, its getting more confused than it should be with this
particular scenario.
if youre looking to enhance the "child" backref part of this, use
"backref=backref('child', **additional_criterion)".
On Nov 6, 2007, at 3:42 AM, Esceo wrote:
>
> Hi, all
>
> the followings are the code snippet
>
> from sqlalchemy import *
> meta = MetaData('sqlite://')
>
> parent = Table('parent', meta,
> Column('id', Integer, primary_key=True),
> Column('name', Integer)
> )
>
> child = Table('child', meta,
> Column('id', Integer, primary_key=True),
> Column('current_id', Integer),
> Column('parent_id', Integer),
> ForeignKeyConstraint(['parent_id'],['parent.id'],
> ondelete="CASCADE"),
> ForeignKeyConstraint(['current_id'],['child.id']), )
>
> class Parent(object):
> pass
>
> class Child(object):
> pass
>
> mapper(Parent, parent);
>
> mapper(Child, child,
> properties = { 'parent' : relation(Parent,
> primaryjoin =
> (child.c.parent_id == parent.c.id) &
> (child.c.current_id ==
> child.c.id),
> backref = "child"),
> 'current' : relation(Child,
> primaryjoin = child.c.current_id ==
> child.c.id)
> })
>
> meta.create_all()
>
> s = create_session()
> c = Child()
> c.parent = Parent()
> s.save(c)
> s.flush()
> s.clear()
>
> running that resulted in
>
> Traceback (most recent call last):
> File "C:\powerforce\test_fk_relation.py", line 39, in <module>
> s.flush()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\session.py", line 320, in flush
> self.uow.flush(self, objects)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 210, in flush
> flush_context.execute()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 400, in execute
> UOWExecutor().execute(self, head)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 1018, in execute
> self.execute_save_steps(trans, task)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 1035, in
> execute_save_steps
> self.execute_dependencies(trans, task, False)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 1048, in
> execute_dependencies
> self.execute_dependency(trans, dep, False)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 1029, in
> execute_dependency
> dep.execute(trans, isdelete)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\unitofwork.py", line 984, in execute
> self.processor.process_dependencies(self.targettask, [elem.obj for
> elem in self.targettask.polymorphic_tosave_elements if elem.obj is not
> None], trans, delete=False)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\dependency.py", line 275, in
> process_dependencies
> self._synchronize(obj, child, None, False, uowcommit)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\dependency.py", line 310, in _synchronize
> self.syncrules.execute(source, dest, obj, child, clearkeys)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\sync.py", line 92, in execute
> rule.execute(source, dest, obj, child, clearkeys)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\sync.py", line 135, in execute
> value = self.source_mapper.get_attr_by_column(source,
> self.source_column)
> File "C:\Python25\lib\site-packages\SQLAlchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\mapper.py", line 1017, in get_attr_by_column
> prop = self._getpropbycolumn(column, raiseerror)
> File "C:\Python25\lib\site-packages\SQLAlchemy-0.3.11dev_r3181-
> py2.5.egg\sqlalchemy\orm\mapper.py", line 1007, in _getpropbycolumn
> raise exceptions.InvalidRequestError("Column '%s.%s' is not
> available, due to conflicting property '%s':%s" % (column.table.name,
> column.name, column.key, repr(prop)))
> sqlalchemy.exceptions.InvalidRequestError: Column 'child.id' is not
> available, d
> ue to conflicting property
> 'id':<sqlalchemy.orm.properties.ColumnProperty object at 0x016FB730>
>
> If I had renamed the id column on child to '_id', I ended up with a
> different error no child.id column configured on the maper Parent|
> parent|
>
> any clues?
>
> Thanks in advance
>
> Lei
>
>
> >
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