Skip to main content

Changed rendering (and evaluation) behaviour in APEX 4.2

By
Today we ran into a problem in our recently upgraded APEX environment. In one of the pages we had a report defined on a pipelined table function. This function also changed a package global variable. The value of that global variable is used as a source for a page item that shows up in the same region just below the report. This ran fine in 4.1, it runs fine when we set the "Compatibility Mode" to 4.1 as well. But if we set that mode to 4.2...the page item shows...nothing !!!

What happened? According to the help on that Compatibility Mode property, items (and regions) in a display point are evaluated before rendering that display point. This is done to find out whether items / regions are displayed or not - to support the grid layout. To dig a little deeper (thanks to Patrick Wolf, who was helping us with this issue): As soon as the region grid is calculated, the same is done for the page item grid in the region which gets painted next. This calculation also has to determine the page item values, because they could be used in a condition of one of the following page items. This is all done before the region source is actually executed.

So, in our case, the value of the page item - what was based on the result of the pipelined table function - was evaluated before that pipelined table function was actually executed...and therefore returned null. We could easily spot that in the debug output: When we compared the order of evaluations of the region and the items we saw a (huge) difference in 4.1 and 4.2 mode.

So now we know what caused the issue. But how to solve it?
We created a PL/SQL sub region to the reports region and moved the page item to that subregion. That was not enough to evaluate the page item value after running the report. So we removed the PL/SQL source of that page item and moved it to the source of it's PL/SQL region. Even that didn't work out. But when we set the Item Display Position to "Below Content", we - finally - saw that the item was evaluated and rendered in the right position of the complete page flow....

So when you notice - similar -  strange behaviour when running your upgraded pages in 4.2, it is worthwhile to check the difference in evaluation and rendering order is the cause of that!

Comments

SydOracle said…
Wonder if that was the same issue that hit the plsqlchallenge website when they upgraded.

http://plsql-challenge.blogspot.com.au/2012/11/upgraded-to-apex-42-andgoodbye-website.html
10:37 am
Roel said…
Might be...I don't kow. It seems they applied some kind of patch.
10:43 am
Post a Comment

Popular posts from this blog

How to create neatly formatted Excel documents using PL/SQL?

By
If there is a requirement to produce output from an application into Excel, you would probably create a CSV (Comma Separated File) with the data and start Excel to show the data - at least that's what I did...until now. The drawback of this solution is that you could only produce data and no nice layout. But Excel is also capable of opening HTML-files and using this you could create Excel files with data and magnificent layout! Let me give an example: 1. Create a procedure to show the data in formatted in an HTML table. CREATE OR REPLACE PROCEDURE display_emp_list IS v_emp_count NUMBER(5); v_empno NUMBER(8); v_ename VARCHAR2(50); v_job emp.job%TYPE; v_sal emp.sal%TYPE; v_bg_color VARCHAR2(10) := ''; CURSOR c_emp IS SELECT empno, initcap(ename), job, sal FROM emp ORDER BY ename; BEGIN SELECT COUNT(*) INTO v_emp_count FROM emp; owa_util.mime_header('application/ms-excel', FALSE); htp.p('Content...
21 comments
Read more

Refresh selected row(s) in an Interactive Grid

By
In my previous post I blogged about pushing changed rows from the dabatase into an Interactive Grid . The use case I'll cover right here is probably more common - and therefore more useful! Until we had the IG, we showed the data in a report (Interactive or Classic). Changes to the data where made by popping up a form page, making changes, saving and refreshing the report upon closing the dialog. Or by clicking an icon / button / link in your report that makes some changes to the data (like changing a status) and ... refresh the report.  That all works fine, but the downsides are: The whole dataset is returned from the server to the client - again and again. And if your pagination size is large, that does lead to more and more network traffic, more interpretation by the browser and more waiting time for the end user. The "current record" might be out of focus after the refresh, especially by larger pagination sizes, as the first rows will be shown. Or (even wors...
Post a Comment
Read more

APEX ReadOnly Pages - The easy way

By
If your Oracle APEX Application requires different types of access - full access or readonly - for different types of users, you can specify a Read Only Condition on Page level (or Region, Item, Button, etc.).  You can set an Authorization Scheme on Application level, so it'll be applied to all pages. So if you have an Authorization Scheme named 'User Can Access Page' defined by a PL/SQL function like this: return apex_authorization.user_can_access_page ( p_app_id  => :APP_ID , p_page_id => :APP_PAGE_ID , p_user    => :APP_USER );  then you can code all the logic in the database using the APEX Repository, your own tables or a combination to define whether a user has access to that page or not. But alas it is not possible to define something similar Application wide for a Read Only condition. You can specify an Authorization Scheme 'User has Read Only Access' using a similar signature as the one above and use that on each and e...
Post a Comment
Read more