Order by clause require dynamic value

Question

Hi
I want to bind parameters to orderby clause. In where clause with bind parameter works fine. But in orderby clause ive done similar steps to have a dynamic sort which will be passed from the previous page in a session variable. Although it didnt show any error at the backend where i can see data getting binded, but no sorting is taking place.
Can u help me to solve this.
regards
Jayashri

Answer 1

Jayashri,
I have tested this and you are right. And there does occur an error at the backend, only you wont see it unless you run with BC4J debug mode turned on. You can do this by providing -Djbo.debugoutput=console to the JVM. When running inside JDeveloper, you can accomplish this by going to Project Properties => PRofiles => Development => "Runner", and fill this in at the "Java Options" field.
Doing that will show the reason of the problem. When a view object is queried, BC4J actually performs 2 queries. One to obtain the 'estimated row count', and then one to obtain the action rows.
Now suppose your query looks like this:
SELECT <somefields> FROM <table>
WHERE <field> = :1 ORDER BY :2
Bc4j will construct the following query to obtain the estimated rowcount:
SELECT count(1) FROM (SELECT <somefields> FROM <table> WHERE <field> = :1)
As you can see, it does NOT include the ORDER BY of the original query in this statement, probably for performance reasons (why order the set if you are only interested in the count). Unfortunately, it WILL try to bind both :1 AND :2 to this query, but because there is only one bind variable in this query, this throws an java.sql.SQLException which is unfortunately trapped somewhere in BC4J code, and not shown in the regular log file.
I am pretty confident that this is actually a BC4J bug (or known restriction). You could post this problem at the JDeveloper Forum to determine this (without mentioning JHeadstart, because this would also happen if you wrote your own code for binding these parameters).
As for a workaround, you could try the following:
1.) Remove the (bind parameter from) the order by clause on the ViewObject
2.) Remove that same bind parameter from the "Query Bind Parameters" property.
You should now have gone back to a scenario where there are only bind parameters on the where clause. You would need to set the OrderBy clause programatically now. To do this, extend the JhsDataAction for this page, and override the method 'applyIterBindParams()'. Before calling super, try something like:
ViewObject vo = ib.getRowSetIterator().getRowSet().getViewObject();
vo.setOrderByClause(<your dynamic orderby>);
Kind regards,
Peter Ebell
JHeadstart Team