Tips for APEX Application Constants

How to use Text Messages for Constants

PublishedJanuary 22, 2024

Comments (5)

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Reckson Zirsangzela Khiangte2y ago

Very insightful

Jari Laine2y ago

Hi Martin,

I have two cases that like understand does write to database happens:

If I create hidden item P0_APP_NAME to global page and set Storage to Per Request (Memory Only). Then create application computation before header for item.
I have hidden item P1_EMPNO where Storage set Per Request (Memory Only), and I use item in classic report Page Items to Submit. Then e.g. sort report.

Thanks advance.

Martin Giffy D'Souza2y ago

Jari Laine in both cases the items will be written to "APEX Session memory" in the database. Here are the reasons:

1: When you have a application computation, the processing is done in the database and therefore is saved in your APEX Session

2: When the item is set to Page Items to Submit the same occurs. It's sent via the AJAX request, stored in APEX Session then is used in the request.

Osvaldo González2y ago

Hello Martin, this post is very good. I have a doubt. ¿Can I use this with a computation instead of a application item to save the username? Because I'm using database user and not APEX user

Martin Giffy D'Souza2y ago

Text messages are stored for the entire application (i.e. they aren’t session specific). You shouldn’t use it to store session specific content. So I wouldn’t recommend for username.

Osvaldo González2y ago

Martin Giffy D'Souza thanks for your response

Jon Dixon2y ago

Nice, thanks Martin.

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Solution

To avoid the additional overhead you can use a Text Message. Text Messages are primarily intended for translation purposes however they also allow developers to have configurable application constants. Text messages are different than Application Settings in the sense that they can be referenced in APEX as a substitution string.

The following example shows how to use text messages for this purpose.

Go to Shared Components > Text Messages

Click Create Text Message and add the following:

On the login page (or this can be anywhere in the application where you want a dynamic application name) change the region title to: &APP_TEXT$APP_NAME. More information about referencing text messages as substitution strings can be found in docs.

When the page is run it shows Demo Dev as expected:

To change this in other environments it's unrealistic to set the value via the APEX application builder as most developers won't have access to Test and Prod instances. Instead it can be easily set through the API apex_lang.update_message As part of your release process after the APEX application has been update the following code should be run to set the value:

declare c_apex_app_id apex_application_translations.application_id%type := 200; l_translation_entry_id apex_application_translations.translation_entry_id%type; begin select aat.translation_entry_id into l_translation_entry_id from apex_application_translations aat where 1=1 and aat.application_id = c_apex_app_id and aat.translatable_message = 'APP_NAME' ; -- Detect if in APEX already -- Usually necessary as this should be run as a post-install script in SQLcl -- -- If you're not in an APEX application you'll get following error: -- ORA-20001: Package variable g_security_group_id must be set. -- -- May get ORA-20987: APEX - An API call has been prohibited. -- If so go to Shared Components > Security Attributes -- Check box: Runtime API Usage > Modify This Application -- if apex_application.g_flow_id is null then apex_session.create_session ( p_app_id => c_apex_app_id, p_page_id => 1, p_username => 'dummy' ); end if; -- Set text message: apex_lang.update_message ( p_id => l_translation_entry_id, -- Note: This value should come from a lookup table p_message_text => 'Dev Test' ); -- Commit is required for changes to take affect commit; end; /

After running this script the login page will show the update application name:

Closing Remarks

I've used this technique in a very high-use application that can have between 300,000 ~ 500,000 sessions a day. The application has about 10 application constants. If Application Items were used for these constants it would result in 10 x 500,000 (5 Million) unnecessary extra writes occurring every day to store values that don't change.

I also found that there were some places "regular" substitution strings did not work (using an Application Item or Page Item) but worked for Text Messages. These were extreme edge cases.

When this technique is used you need to ensure that you have a good release process. I.e. right after the APEX application is installed/updated in each environments the text messages need to be updated as they will contain the "original" text message from the application export.

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Solution

Closing Remarks