Hi,
I have some questions concerning ordered relations in JDO:
1. Suppose that you have two classes: Point (e.g. a town) and Path,
where the later represents a walk touching some Points.
The relation is many to many, in the sense that a Path touches many
points and a Point could be touched by many Paths.
The relation is also ordered (on Points) in the sense that you want to
know the order in which the points are visited.
I expect to have a class Path with an ordered sturcture (e.g. a Vector)
where each the i-th entry is the Point vistited at i-th step.
In the database, I think I have to store these informations in three
tables (points, paths, paths_points_r), where
paths_points_r has columns path_id (foreing key for id in paths table),
point_id (FK for id in points) an integer column used to describe the
order, e.g.:
PATH_ID POINT_ID STEP
1008 999 1
1008 800 2
1008 801 3
...
the question is: is it possible to map such a database structure in JDO
so that the ordered collection used in the class Path satifies
the requirement exposed above ?
2. generally speaking is it possible to have an ordered relation
(implemented in some other way) in JDO ?
3. is it possible to add an "ORDER BY" clause to the SQL statement
produced by JDO to load objects ?
best regards, alessandro.
--
Alessandro Dimauro
Research and Technologies Area
SODALIA s.p.a.
v. Valentina Zambra,1 38100 TRENTO ITALY
phone: +39 0461 316110 fax: +39 0461 316401
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