Ordering related collections

Question

Hi,
I have a one-many relation between two classes whereby the child class's
primary key consists of two fields: the parent class's oid and an entry
date.
Is there a mechanism that can be used to get an "ORDER BY" clause included
in the SQL that is issued when my program follows my relationship?
I always want my collection of children to be ordered by the entry date,
but instead, there appears to be no ordering as two subsequent references
to the same collection often results in a different ordering of the
collection elements.
Thanks,
Bill

Answer 1

William-
It seems like you want to use the jdbc-ordered extension. See:
http://docs.solarmetric.com/manual.html#jdbc-ordered
Note that Kodo will require that you have an additional column that
holds the order for the collection.
In article <[email protected]>, William Korb wrote:
In re-reading my original post, I decided it wasn't very clear. Perhaps an
example of what I'm asking for might make this a bit more clear.
Customer {
int customerId;
// other stuff
Order {
int customerId; // fkey to Customer table
Date orderDate;
// other stuff
OK, so when I want to get all of the orders for a customer, I use the
mapping keyed by the customerId field in the Order.
Customer c = getCustomerFromSomewhere();
Iterator ordersIterator = c.orders.iterator();
Let's say that I have a customer with two orders, one dated June 1 and one
dated June 2. When I step through the ordersIterator, sometimes the June 1
order will be first, and sometimes the June 2 order will be first. I would
very much like this ordering to be consistent. If I manually select my
orders with a JDOQL query where customerId == something, I can then
specify an order by clause, but this defeats the purpose of the ability to
traverse the relationships between JDO objects.
I realize that I can simply sort the returned orders, but there are
performance reasons for preferring that the database do this for me (e.g.,
result set is large, relationship is being referenced from within a JSTL
forEach tag, etc.). Also, this is a pre-existing schema, so I cannot add
an integer order column to define the natural ordering of the results.
Is there an easy answer?
Thanks,
Bill
William Korb wrote:
Hi,
I have a one-many relation between two classes whereby the child class's
primary key consists of two fields: the parent class's oid and an entry
date.
Is there a mechanism that can be used to get an "ORDER BY" clause included
in the SQL that is issued when my program follows my relationship?
I always want my collection of children to be ordered by the entry date,
but instead, there appears to be no ordering as two subsequent references
to the same collection often results in a different ordering of the
collection elements.
Thanks,
Bill
Marc Prud'hommeaux
SolarMetric Inc.