Using Enter-Query Mode Programmatically

Question

A question was raised in an earlier thread
QUERY CRITERIA MANAGER
about how to use Enter-Query mode programmatically in a way that doesn't stop
and prompt the user to enter a query after switching from Normal mode to Enter-Query mode.
Since the solution may not be widely known, I thought I'd demonstrate the technique here in a new thread.
Create a simple form with just two blocks. Using the data block wizard, create an EMP block with one
text item for ENAME. Place it on the canvas. Create the other block as a control block and name it CONTROL.
Inside the control block create the following items:
- create a text item named TXT_BOX
(The user will enter their search pattern criteria in this text box while in Normal mode.)
- create a push button item named EXECUTE_QUERY
(This button will switch to Enter-Query mode, execute the query, then return to Normal mode.)
Place both control items on the canvas.
Inside the WHEN-BUTTON-PRESSED trigger for the EXECUTE_QUERY button, enter the following code:
DECLARE
     timer_id TIMER;
BEGIN
     :GLOBAL.search_criteria := :CONTROL.TXT_BOX;
     GO_BLOCK('EMP');
     timer_id := CREATE_TIMER('ENT_QRY', 1500, NO_REPEAT);
     -- 1500 may be a little long, but provides a margin of error
     ENTER_QUERY;
END;
Next, create a WHEN-TIMER-EXPIRED trigger at the form level. Inside this trigger enter the following code:
If GET_APPLICATION_PROPERTY(TIMER_NAME) = 'ENT_QRY' THEN
     :EMP.ENAME := :GLOBAL.search_criteria;
     EXECUTE_QUERY;
     IF :SYSTEM.MODE = 'ENTER-QUERY' THEN
          EXIT_FORM; -- return to Normal mode
     END IF;
END IF;
GO_ITEM('CONTROL.TXT_BOX');
Now, when the user runs the form and logs into the SCOTT schema, he enters a search criteria
such as A% in the TXT_BOX while in Normal mode. Then clicks the EXECUTE_QUERY button.
The form will switch to Enter-Query mode, retrieve all names in ENAME that begin with the letter A,
and then return to Normal mode without pausing for the user to enter a search criteria.
If the query should happen to fail, the form displays the error:
"FRM-40301: Query caused no records to be retrieved. Re-enter."
then switches automatically back to Normal mode so the user can try entering a new criteria.

Answer 1

I'm showing how to do it when switching modes. I'm
not suggesting this is the best way to do a query.We need to look at this in the context of the original probelm in the thread linked to above. For most cases the when-timer-expired etc is just a huge detour around using the pre-query trigger but it's an interesting approach to the specific problem in the earlier thread. The OP there wanted to be able to type '>5000' into a number field in a non-database block, which we can do in a database block in enter-query mode, and use it as a query parameter in the database block. Perhaps if we enter this into a character field in the non-database block and populate the numeric field in the database block whilst in enter-query mode then we can do searches on ranges of data? Unfortunately it doesn't work - you get an ora-06502 error just like you do when using the pre-query trigger. For the situation in the original thread you would have to use a 'default where'.