Thanks for your answer first.
Root is a singleton, its class is not mapped to a table.
What I mean is I could add a table "roots" to the database with a
sigle row and add areas a foreign key "root_id" and create a
relationship as from subareas with parent area and get what I'm
talking about.
This relationship, between root and area, as long as areas and
subareas would come in handy for example to traverse the tree for
extracting an xml simply, or to make recursive calculations.
Before sqlalchemy I was used to add all areas, subareas, items, parent
attributes to classes by myself but now I'm in the situation that 80%
of the work is done by sqlalchemy automatically and I'm not sure how
to fill the remaining, possibly having both areas and subareas behave
at the same way to avoid confusion (just as an example, lazy loading).
Thanks for your support
neurino
On Nov 15, 3:49 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
> On Nov 15, 2010, at 8:06 AM, neurino wrote:
>
> > So no advice?
>
> > Are relationships and backref something more than attributes I can
> > setup with a query?
>
> > Thank you for your support.
>
> what's not stated clearly here is what "Root" is. If that's not a class
> mapped to a table, then you'd just need to use regular Python attributes and
> descriptors to establish the in-python behavior you're looking for. Seems
> like its essentially some kind of query object, so your query.all()/.parent =
> some_root approach is what you'd go with, though it would appear that Root is
> a singleton anyway, meaning this could be established on Area at the class
> level instead of assigning to each instance.
>
> Its not clear what other behavior of "relationship()" would apply here, since
> Root has no database identity.
>
>
>
>
>
> > On Nov 11, 9:45 am, neurino <neur...@gmail.com> wrote:
> >> I have a tree structure
>
> >> Root
> >> |
> >> +--Area
> >> | |
> >> | +--SubArea
> >> | | |
> >> | | +--Item
> >> | | |
> >> | | +--Item
> >> | |
> >> | +--SubArea
> >> | |
> >> | +--Item
> >> | |
> >> | +--Item
> >> |
> >> +--Area
> >> |
> >> +--SubArea
> >> | |
> >> | +--Item
> >> | |
> >> | +--Item
> >> |
> >> +--SubArea
> >> |
> >> +--Item
> >> |
> >> +--Item
>
> >> The tree structure corresponds to slqalchemy db tables `areas`,
> >> `subareas` and `items`.
>
> >> Something like this:
>
> >> mapper(Area, areas_table, properties={
> >> 'subareas': relationship(SubArea, backref='parent'),
> >> })
> >> mapper(SubArea, subareas__table, properties={
> >> 'items': relationship(Item, backref='parent'),
> >> })
> >> mapper(Item, items_table)
>
> >> so each Area instance will have a `subareas` list and each SubArea
> >> will have a `items` list,
>
> >> also I easyly get a backref `parent` from Item to parent SubArea and
> >> from
> >> SubArea to parent Area.
>
> >> But this won't be for Root: it will not have a `areas` list in Root
> >> nor its areas will have a parent reference to Root.
>
> >> The quick-and-dirty solution is to do this in Root:
>
> >> self.areas = query(Area).all()
> >> for area in self.areas:
> >> area.parent = self
>
> >> But it won't be the same thing as sqlalchemy `relationship` attributes
> >> so:
> >> are there alternative solutions more sqlalchemy-like?
>
> >> Any tip appreciated!
>
> >> Thank you for your support
>
> >> Greetings
> >> neurino
>
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