How to show a database trigger error message as a notification on a page

Question

I have a database with database triggers to ensure data integrity.
If an insert or update does not comply to all the business rules, a database triggers raises an exception. When using Apex this exception is caught in the Error Screen, a separate screen, where the whole error stack is displayed.
Does anyone know a way to display only the error in RAISE_APPLICATION_ERROR as a notification in the screen from which the transaction was initiated?
Dik Dral

Answer 1

Well, having had so little response, i had to figure it out myself ;-)
Using Patrick Wolff's ideas from ApexLib I 'invented' a solution for my problem, that I would like to contribute to the community. I hope that it will come out a bit nicely formatted:
Apex: Show Database Error Message in calling form
The purpose is to show a neat error message in the notification area of the calling form.
Default Apex show the whole error stack raised by a DB trigger in a separate error page.
With acknowledgement to Patrick Wolf, I lent parts of his ApexLIB code to create this solution.
<br./>
Assumptions
<ul><li>The error message is raised from a DB trigger using RAISE_APPLICATION_ERROR(-20000,’errormessagetext’).</li>
<li>The relevant part of the error stack is contained within the strings ‘ORA-20000’ and the next ‘ORA-‘-string, i.e. if the error stack is ‘ORA-20000 Value should not be null ORA-6502 …’, than the relevant string is ‘Value should not be null’ .</li>
<li>Cookies are enabled on the browser of the user </li>
</ul>
Explanation
The solution relies heavily on the use of Javascript. On the template of the error page Javascript is added to identify the error stack and to extract the relevant error message. This message is written to a cookie, and then the control is passed back to the calling page (equal to pushing the Back button).
In the calling page a Javascript onLoad process is added. This process determines whether an error message has been written to a cookie. If so the error message is formatted as an error and written to the notification area.
Implementation
The solution redefines two template pages, the two level tab (default page template) and the one level tab (error page template).
Javascript is added to implement the solution. This Javascript is contained in a small library errorHandling.js:
<pre>
var vIndicator = "ApexErrorStack=";
function writeMessage(vMessage)
{       document.cookie = vIndicator+vMessage+';';
function readMessage()
{ var vCookieList = document.cookie;
var vErrorStack = null;
var vStart = null;
var vEnd = null;
var vPos = null;
vPos = vCookieList.indexOf(vIndicator);
// No cookie found?
if (vPos == -1) return("empty");
vStart = vPos + vIndicator.length;
vEnd = vCookieList.indexOf(";", vStart);
if (vEnd == -1) vEnd = vCookieList.length;
vErrorStack = vCookieList.substring(vStart, vEnd);
vErrorStack = decodeURIComponent(vErrorStack);
// remove the cookie
document.cookie = vIndicator+"; max-age=0";
return(vErrorStack);
function getElementsByClass2(searchClass,node,tag)
var classElements = new Array();
if ( node == null )
node = document;
if ( tag == null )
tag = '*';
var els = node.getElementsByTagName(tag);
var elsLen = els.length;
var pattern = newRegExp('(^|\\s)'+searchClass+'(\\s|$)');
for (i = 0, j = 0; i < elsLen; i++) {
if ( pattern.test(els.className) ) {
classElements[j] = els[i];
j++;
return classElements;
function processErrorText()
var errorElements = new Array();
errorElements = getElementsByClass2("ErrorPageMessage",document,"div");
if (errorElements.length > 0 )
{ errorText = errorElements[0].innerHTML;
errorText = errorText.substr(errorText.indexOf("ORA-20000")+ 11);
errorText = errorText.substr(0,errorText.indexOf("ORA")-1);
// errorElements[0].innerHTML = errorText;
writeMessage(errorText);
function show_message()
{ var vCookieList = document.cookie;
var vErrorStack = null;
var vErrorName = null;
var vErrorMessage = null;
var vStart = null;
var vEnd = null;
var vPos = null;
// get errorStack
vErrorStack = readMessage();
if (vErrorStack == -1) return;
// search for our message section (eg. t7Messages)
var notificationArea = document.getElementById("notification");
if (notificationArea != null)
{ notificationArea.innerHTML = '<div class="t12notification">1 error has occurred<ul class="htmldbUlErr"><li>' + vErrorStack + '</li></ul>'; }
else
{ alert(vErrorStack); }
</pre>
This code is loaded as a static file in Application Express (no application associated).
In both templates a reference to this code is added in the Definition Header section:
<pre>
<script src="#WORKSPACE_IMAGES#errorHandling.js" type="text/javascript"></script>
</pre>
This library is called from the two level tab to show the error message (if any) in het onLoad event of the body tag.
<body onLoad="javascript:show_message();">#FORM_OPEN#
This code checks whether a message has been written to a cookie and if found displays the message in the notification area.
In the error template page the Error section has the content:
<script language="javascript">
processErrorText();
window.history.go(-1);
</script>
Back
The call to processErrorText() looks for the error message, extracts the relevant part of it (between ‘ORA-20000’ and the next ‘ORA-‘), writes it to a cookie and returns to the previous screen.
The link to the previous page is added should an error in the Javascript occur. It provides the user with a path back to the application.
With these actions taken, the error messages issued from triggers are shown in the notification area of the form the user has entered his data in.
The need for database driven messaging
In some cases the need exists to process error messages in the database before presenting them to the user. This is the case, when the triggers return message codes, associated to error messages in a message table.
This can be done by using a special Error Message Processing page in Apex.
The error message page extracts the error message, redirecting to the Error Message Processing page with the error message as a parameter. In the EMP page a PL/SQL function can be called with the message as a parameter. This function returns the right message, which is written to a cookie using dynamically generated Javascript from PL/SQL. Than the contol is given back to the calling form.
The redirect is implemented by location.replace, so that the error message page does not exist within the browsing history. The normal history(-1) will return to the calling page.
Implementation of database driven messaging
The solution redefines two template pages, the two level tab (default page template) and the one level tab (error page template).
Javascript is added to implement the solution. This Javascript is contained in a small library errorHandling.js already listed in a previous paragraph.
In both templates a reference to this code is added in the Definition Header section:
<script src="#WORKSPACE_IMAGES#errorHandling.js" type="text/javascript"></script>
This library is called from the two level tab to show the error message (if any) in het onLoad event of the body tag.
<body onLoad="javascript:show_message();">#FORM_OPEN#
This code checks whether a message has been written to a cookie and if found displays the message in the notification area.
In the error template page the Error section has the content:
<script language="Javascript">
var errorText = null;
function redirect2oracle()
{ window.location.replace("f?p=&APP_ID:500:&APP_SESSION.::::P500_MESSAGE:"+errorText); }
function getError()
{ errorText = processErrorText(); }
getError();
redirect2oracle();
</script>
Go to Error Message Porcessing Page
Back to form
The call to processErrorText() looks for the error message, extracts the relevant part of it (between ‘ORA-20000’ and the next ‘ORA-‘), writes it to a cookie.
Then the EPM-page (500) is called with the extracted message as parameter.
The link to the EPM page and the previous page is added should an error in the Javascript occur. It provides the user with a path back to the application.
We need to create an Error Message Porcessing Page.
Create a new page 500 with a empty HTML-region “Parameters”
Create an text-area P500_MESSAGE in this region
Create a PL/SQL region “Process Messages” with source:
convert_message(:P500_MESSAGE);
Create a PL/SQL procedure convert_message like this example, that reads messages from a message table. If not found, the actual input message is returned.
CREATE OR REPLACE procedure convert_message(i_message in varchar2) is
v_id number := null;
v_message varchar2(4000) := null;
function get_message (i_message in varchar2) return varchar2 is
v_return varchar2(4000) := null;
begin
select msg_text into v_return
from messages
where msg_code = upper(i_message);
return(v_return);
exception
when no_data_found then
return(i_message);
end;
begin
v_message := get_message(i_message);
// write the message for logging/debugging
htp.p('Boodschap='||v_message);
// write cookie and redirect to calling page
htp.p('<script language="Javascript">');
htp.p('document.cookie="ApexErrorStack='||v_message||';";');
htp.p('window.history.go(-1);');
htp.p('</script>');
// enter return link just in case
htp.p('Ga terug');
end;
Note: The way the message is converted is just an example
With these actions taken, the error messages issued from triggers are shown in the notification area of the form the user has entered his data in.
Message was edited by:
dickdral
null