itll probably work better with a backreference; that way the two-way
relationship of "parent" and "child" is better managed (its also more
succinct syntactically).
the docs should probably be changed to illustrate this example since
its more common than the "root" example it shows.
in the SA distribution theres an "examples" directory which has three
self-referential example scripts. both the "examples/adjacencytree/
basic_tree.py" and the "examples/backref/backref_tree.py" examples
have the "parent"/"childlist" two-way relationship managed by a
backref (these two examples are actually somewhat redundant and
should be grouped together).
so you would do it like this:
mapper(Project, projects,
properties={
'child_projects':relation(
Project,
primaryjoin=projects.c.id==projects.c.parent_project_id,
foreignkey=projects.c.parent_project_id,
backref=backref('parent_project', foreignkey=projects.c.id)
)
}
)
the "byroot_tree" example is much more intricate example than the
previous two, and is more like the one in the documentation; if you
ask why the "byroot_tree" example doesnt use a backref, its because
the node doesnt have a "parent" attribute, it has a "root" attribute
instead which indicates the rootmost node in the node's subtree, and
which is managed by some explicit code in the TreeNode class itself
as well as a mapper extension. so dont worry about that one.
On Jun 6, 2006, at 11:23 PM, Randall Smith wrote:
> I have a table with a foreign key to itself. The foreign key
> references
> it's parent record. I would like the table mapped to an object
> that has
> both a parent and children attribute. I've been going by the treenode
> example in the docs. I can get either children to work or parent to
> work, but not both. In other words, if I say parent.append(child),
> child.parent is NULL. If I say child.parent = parent, parent.children
> is an empty list.
>
> My table def and mapper:
>
> projects = Table('projects', metadata,
> Column('id', INTEGER, primary_key=True),
> Column('title', VARCHAR(200), nullable=False),
> Column('county_code', INTEGER, nullable=False),
> Column('pws_id', INTEGER),
> Column('project_type', VARCHAR(100), PassiveDefault('Standard'),
> nullable=False),
> Column('description', TEXT),
> Column('reviewer_id', INTEGER, nullable=False),
> Column('reviewer_name', VARCHAR(100), nullable=False),
> Column('pro_engineer_id', INTEGER),
> Column('pro_engineer_name', VARCHAR(100)),
> Column('notes', TEXT),
> Column('parent_project_id', INTEGER,
> ForeignKey("%s.projects.id" % schemaname)),
> Column('input_time', TIMESTAMP, timestamp_default,
> nullable=False),
> schema=schemaname
> )
>
> mapper(Project, projects,
> properties={
> 'parent_project':relation(Project,
> primaryjoin=projects.c.id==projects.c.parent_project_id,
> foreignkey=projects.c.id),
> 'child_projects':relation(Project,
> primaryjoin=projects.c.id==projects.c.parent_project_id,
> foreignkey=projects.c.parent_project_id)
> }
> )
>
> Any pointers appreciated.
>
> Randall
>
>
>
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