Monday, November 8, 2010

Refresh Report Region and Pagination

When using the refresh action to refresh reports in Oracle APEX 4.0, you inevitably will encounter the problem of lost pagination. The refresh action does really refresh, regardless of which page of the report the user was currently watching.

It Just Won't Tell Me
APEX knows the current pagination of a report. If you go to another page and back, or just press F5, you will see that APEX knows which page of your report you were on. Where can I get that user data? I have looked at the documented API's, and the closest thing I can see, is the apex_application.g_flow_current_min_row. The problem is that this is only available at render time and maps to pg_min_row request value. Otherwise, I only get the value 1 (first row).

It knows, but won't tell me!

The Dirty Approach
If there is a will, there is a way. I looked into the APEX tables, and especially wwv_flow_data. If you look, you will see a record containing the user session instance and report region id. Item value will be a colon separated value starting with the current min row, followed by current max rows (probably). That looks useful, but you need to keep your head about this. The value column is a CLOB data type, and a pretty special format, so if you attempt to use that data, be prepared to do a rewrite next time you patch your APEX installation.

If you notice in your pagination scheme, the pagination link executes a javascript called $a_report_Split (basically a wrapper for old (but rewritten) $a_report). So if I could use wwv_flow_data to get the second parameter of $a_report_Split right (<pMin>_<pMax>_<pFetched>), then I would be good to go..? For a while, anyway. $a_report_Split is not a documented API javascript function, and may also be subject to change in the upcoming releases

The Dirty Solution
Access to wwv_flow_data directly is not something you want to do in a normal APEX installation. Creating a very single minded function in a privileged schema (granted select on wwv_flow_data) and granting access to the function to my application schema was the best I could come up with.
create or replace function <privileged schema user>.get_current_pagination (    
         p_region_id    in       number
      ) return varchar2 is

         l_ret          varchar2(255);
         l_session_id   number := v('SESSION'); -- setting directly prevents unauthorized use
         l_value_tab    apex_application_global.vc_arr2;

         cursor c_region (
            b_session_id      in       number
         ,  b_region_id       in       number
         ) is 
            select item_value
              from apex_040000.wwv_flow_data
            where  flow_instance = b_session_id
              and  item_id = b_region_id;
         for r in c_region(l_session_id,p_region_id)
            l_value_tab := apex_util.string_to_table(r.item_value,':');
         end loop;

         if l_value_tab.exists(1)
            l_ret := l_value_tab(1) || '_' || l_value_tab(2) || '_' || l_value_tab(2);
         end if;
         return l_ret;

      grant execute on <privileged schema user>.get_current_pagination to <application schema user>;
That taken care of, the next thing is to get that value and use it in a call to $a_report_Split.

Follow these steps in your APEX builder:
  • Create two hidden page items called P1_REPORT_REGION_ID and P1_REPORT_SPLIT_PARAMS
  • Create a dynamic action to be called when you would like your report to be refreshed
  • Create three true actions:
  • First action to set P_REPORT_REGION_ID with the id of the report region:
    Action: SetValue, Type: Javascript Expression, Javascript Expression: $('#<report region static id>').closest('div').attr('id').replace(/[^0-9]/g,'').
    (If you set this item value as a computation before header in APEX, you can skip this action)

  • Second action is to set P1_REPORT_SPLIT_PARAMS with values corresponding to the current report page:
    Action: SetValue, Type: PL/SQL Function Body, PL/SQL Function Body: return <privileged schema user>.get_current_pagination(:p1_report_region_id);

  • Third action is to call the $a_report_Split javascript function:
    Action: Execute Javascript Code, Code: $a_report_Split($v('P1_REPORT_REGION_ID'),$v('P1_REPORT_SPLIT_PARAMS'));

    That should be it.

    Naturally, I have cannot create a demo page on for this, as access to wwv_flow_data is somewhat scarce in that environment (and rightfully so).

    Why Didn't He Just...
    If you know of a better way to do this (and better than refreshing the whole page :-)), then please let me know! And if it is possible through documented API's, that would be grand.

    If this is the closest I get, and any of the APEX team is reading this, then please consider this an enhancement request :-P

    For future reference: Oracle Application Express


    1. Hi HÅVARD

      Funnily enough, I encountered the the same issue recently myself.

      I made an enhancement request at the time to the APEX Development team to expose this information via a PL/SQL package, or alternatively expose reset pagination via a package.
      It's being considered for a 4.02+ release.

      The current workaround is to reset pagination using an unconditional page process to Reset Pagination for the Current Page at the process point On Load - Before Regions.

      This forces users to rely on PPR refreshes for pagination.


    2. Here's a simpler solution :)