On Dec 25, 2008, at 6:45 AM, Wichert Akkerman wrote:
>
> I have a reasonably standard hierarchical datastructure which I'm
> trying
> to store in SQL. The basic model looks like this:
>
> class Page(BaseObject):
> __tablename__ = "page"
> id = schema.Column(types.Integer(), primary_key=True,
> autoincrement=True)
> path = schema.Column(types.Unicode(128), nullable=False,
> index=True)
> children = orm.relation("Page", cascade="all",
> collection_class=attribute_mapped_collection("path"))
>
> This works fine. As shown in the basic_tree example you can configure
> the children relation with eager loading and a join_depth to load
> entire
> tree structure efficiently.
this can't work as stated above. You have a relation() from Page to
itself but no notion of foreign key between the "page" table and
itself is specified. You'll get an error.
> I want to do the reverse: build a relation which returns a list of all
> parents of an object. I figured this would work:
>
> parents = orm.relation("Page", remote_side=[id],
> lazy=False, join_depth=5)
>
> That only returns the first parent, not a list of successive
> parents. Is
> it possible to build that parent list like that?
>
if this is a standard adjacency list relation, Page.parent is a many
to one. Joining up five levels will give you a Parent referencing
its Parent referencing its Parent, etc. To roll those up into a
single set of result columns in a single SQL statement would be very
involved - a recursive iterator would be way easier, i.e.
@property
def parents_iterator(self):
s = self.parent
while s:
yield s
s = s.parent
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