Problem with outer joins and the class indicator/discriminator

Question

Hello,
I am having a problem defining a query in toplink (10.1.3.3).
In the workbench, I have created a parent and 2 child descriptors. The parent is "AbstractValue", the children are "DefaultValue", classified by the discriminator 'DEF', and "OverrideValue", classified by 'OVR', both located in the same table.
Another descriptor (containing a one-on-one mapping to both a "DefaultValue", and a "OverrideValue") needs to be queried for its 'value'.
The way the query should act is: If an override value (row) exists, this one applies for that object. If an override doesn't exist, return the default value.
The query then comes down to (as I have it now):
builder.getAllowingNull("OverrideValue").getAllowingNull("value").ifNull(builder.get("DefaultValue").get("value")).equal(builder.getParameter(VALUE_PARAM));
The problem is that toplink adds the distinction for the different kind of "values" in the where clause WITHOUT checking for null values e.g. it performs an outer join, but then still checks for the discriminator value thus
....t1.ovr_id = t2.id(+) AND t2.discriminator = 'OVR' AND ...
instead of
... LEFT JOIN values t2 ON (t1.ovr_id = t2.id AND t2.discriminator = 'OVR') ...
This leads to the behaviour that the query returns ONLY the objects that have override and default values.
An overview of the queries (simplified)
Toplink, at the moment, returns only results if both override and default values exists:
SELECT t1.id
t1.def_id,
t1.ovr_id
FROM values t2,
parameter t1,
values t0
WHERE nvl(t2.value, t0.value) = 15 AND
t1.ovr_id = t2.id(+) AND t2.discriminator = 'OVR' AND
t1.def_id = t0.id AND t0.discriminator = 'DEF'
Situation Wanted:
SELECT t1.id
t1.def_id,
t1.ovr_id
FROM parameter t1
LEFT JOIN values t2 ON (t1.ovr_id = t2.id AND t2.discriminator = 'OVR')
JOIN values t0 ON (t1.def_id = t0.id AND t0.discriminator = 'DEF')
WHERE nvl(t2.value, t0.value) = 15
Anyone know if there is some statement I am missing to allow an actual outer join on descriptors containing class indicators/discriminators? A possible rewrite?
Thanks in advance,
Rudy

Answer 1

This is a bug in TopLink's outer join support for Oracle. Currently the outer join is put in the where clause, instead of the from clause, as we do on other platforms. You might be able to fix it by changing your OraclePlatform to return false for shouldPrintOuterJoinInWhereClause().
Please log this bug on EclipseLink, or through Oracle technial support.
There is a workaround using,
descriptor.getInhertiancePolicy().setAlwaysUseOuterJoinForClassType(true);
James : http://www.eclipselink.org