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APEX (Multi) Application Settings

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Most applications need some sort of "configuration" table. A simple key-value store where you can put values that might change on a different environment, like URLs, minimal password length, API keys, etc. And very conveniently APEX has this implemented as "Application Settings": A simple table containing a key and a value - and a few other properties like "valid values". In your code you can reference these values using either the apex_application_settings view - that contains all Application Settings in your Workspace - or the apex_app_setting API - that you can use to get or set a value based on the Application Settings Name.

That's all great. Until I ran into this situation: Our "application" consists of 2 APEX applications, one Internal (INT), backoffice kind of application and one external (EXT) facing one. And now I needed to set the Application Setting of the EXT application from the INT application. While I can see the current values of the EXT Application Settings - as the apex_application_settings view shows me all settings in my Workspace, I cannot simply set it using the apex_app_setting API as "This procedure changes the application setting value in the current application". So how can I use that to set that API to set the value in another application?
My first idea was to create a Form Page with a Process calling that API in the EXT app and just link to that Form Page from my INT app. That could have worked if both applications would have used the same Authentication cookie. Which of course they didn't!

So as the API can only set a value in the current application .... I had to switch the current application during a Form process that does the update. And there the apex_session package comes to the rescue!
So upon update, when the Application Setting is not a setting of the current application, I have to detach from the current (APEX) session and create a new session for the other (EXT) application. Then I can set the value using the apex_app_setting API. Once done, I can delete that APEX session and attach back to my original session. So the next processes in my APEX page (like "Close Dialog") will still work. 

begin 
  if :P235_APPLICATION_ID = :APP_ID then         
    apex_app_setting.set_value( :P235_NAME, :P235_VALUE );
  else
    -- Switch to other / new session in the other App
    apex_session.detach;
    apex_session.create_session (p_app_id => :P235_APPLICATION_ID, p_page_id => 0, p_username => :APP_USER);
    apex_app_setting.set_value( p_name => :P235_NAME, p_value => :P235_VALUE );
    apex_session.delete_session;
    -- Return to the original session
    apex_session.attach( p_app_id => :APP_ID, p_page_id => :APP_PAGE_ID, p_session_id => :APP_SESSiON );
  end if;  
end;

Simple. Elegant. And just using the APEX API's! 

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