LEFT OUTER JOIN SQL syntax

Question

Haven't seen a solution to this on the forum or in the docs. My last post timed out with no responses, but I still don't know if I have a possible solution.
I've got 2 objects, Task and Role, that are linked in a M-M relationship.
My tables are:
T_TASKS
T_TASKSROLES
T_ROLES
I am querying T_TASKS and joining on T_TASKSROLES and T_ROLES, but I need to use an outer join because not all Tasks have a Role in T_TASKSROLES.
In SQL Server, my FROM clause SHOULD look like this:
FROM (T_TASKSROLES t2 LEFT OUTER JOIN T_TASKS t1 ON t1.ID = t2.TASKID) LEFT OUTER JOIN T_ROLES t0 ON t0.ID = t2.ROLEID
however, if I use eb.anyOfAllowingNone(_roles) in my ExpressionBuilder. TopLink creates a LEFT OUTER JOIN clause that looks like this:
FROM T_ROLES t0 LEFT OUTER JOIN T_TASKS t1 ON((t0.ID = T_TASKSROLES.ROLEID) AND (t1.ID = T_TASKSROLES.TASKID))
I can see the logic in how it builds this clause. But, it doesn't parse in SQL Server.
Is there a way to effect how TopLink generates the FROM clause for outer joins? I mean, I understand how to use the XXXPlatform.java source files and can change whether to use OuterJoin in the WHERE clause or not. But, I can't see anything in the platform class that would allow me to figure this out.
I realize I could write SQL manually, but is there a way to do this so that the same code would work on SQL Server, Oracle, and Sybase (assuming the DatabaseLogin is configured appropriately)?
It just seems like LEFT OUTER JOIN when joining M-M relationships isn't generating proper SQL. Is the TopLink SQL SQL92-compliant?
I should add that I have tried to change SQLServerPlatform to have shouldPrintOuterJoinInWhereClause() return "true". This embeds a "=*" in the join conditions in the WHERE clause.
SQL Server 2000 still supports this syntax, but the "=*" isn't ALWAYS the correct operator. It is important to put the "*" on the correct side of the expression. TopLink always prints "=*", but the operators are not always in the correct order. So, it tries to create a "left join" on the wrong table.
So my other question, is it possible to force TopLink to remember to put the outer join table in the RIGHT SIDE?
Nate

Answer 1

The workaround is actually more complicated than that, and it can't be fixed by changing only the operator.
In the queries you listed, the only difference is which side of the "AND" the expressions appear on.
Change "(t2.rightid (+)= t1.rightid)" to "(t1.rightid (+)= t2.rightid)" and I'm guessing (although not sure because I am testing with SQL Server at the moment), that you'll get a similar query error as I did.
The bug here is that the default M-M selection criteria creates "reltable = table1 AND table2 = reltable". There is no operator that can satisfy this expression.
So, the fix that I made, for all of my M-M Mappings was to set the SelectionCriteria manually using the following Expression (returned from this method):
// This puts M-M relationship tables on the same side of expressions so that OUTER JOINS can be supported.
private Expression getSameSideExpression() {
          // target side
          Expression selectionCriteria = null;
Enumeration e2 = getTargetKeyFields().elements();
Enumeration e = getTargetRelationKeyFields().elements();
ExpressionBuilder eb = new ExpressionBuilder();
Expression relTableExp = null;
while(e2.hasMoreElements()) {
DatabaseField df = (DatabaseField) e.nextElement();
DatabaseField df2 = (DatabaseField) e2.nextElement();
if(relTableExp == null){
relTableExp = eb.getTable(df.getTable());
Expression targetFieldExp = eb.getField(df2);
Expression relFieldExp = relTableExp.getField(df);
Expression joinExp = relFieldExp.equal(targetFieldExp);
if(selectionCriteria == null)
selectionCriteria = joinExp;
else
selectionCriteria = joinExp.and(selectionCriteria);
          // source side
e = getSourceRelationKeyFields().elements();
          e2 = getSourceKeyFields().elements();
while(e.hasMoreElements()) {
DatabaseField df = (DatabaseField) e.nextElement();
DatabaseField df2 = (DatabaseField) e2.nextElement();
Expression relFieldExp = relTableExp.getField(df);
Expression sourceFieldExp = eb.getParameter(df2);
Expression joinExp = relFieldExp.equal(sourceFieldExp);
if(selectionCriteria == null)
                    selectionCriteria = joinExp;
else
selectionCriteria = joinExp.and(selectionCriteria);
          return selectionCriteria;
This changes the M-M Selection Criteria to "table1 = reltable AND table2 = reltable". Now that this is consistent, using the WHERE clause for my joins in SQL Server is possible.
If you can think of any other problems this change may have, please let me know.
Thanks for the help.
Nate