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XPages bug - computewithform option for data sources with some formula language commands

By Andrew Pollack on 03/01/2012 at 01:07 PM EST

Bug Specifics:

The document you are attempting to save from your XPage may fail to save when the following conditions are all met:

1. You are using the XPage in a web browser (the issue does not seem to happen in the Notes client)

2. You have selected to computeWithForm "On Save" or "On Both" for the bound document ("On Load" does not seem to manifest the bug)

3. There is a computed field on the form which uses the "@UserAccess" function as part of its formula

Note: You can work around this by testing for @isError() on the result of your @UserAccess call to avoid the formula itself producing an error, however this is not necessary in any other context for the use of the @UserAccess function and so would not be something existing code will be testing for.

I found this after way too much effort. Being fairly new to actually trying to do useful things with XPages, I hadn't added a "Display Errors" design control to my page. Big mistake. I'd have saved a lot of trouble for myself if I'd just done that. Once I did, I saw that the attempt to compute the value at save time was generating the error "@Function may not be used in this context". This error is accurate in that it does represent the cause of the error, however it is inaccurate in that the function should work fine within the web browser context, and always has in the past. For this reason, I consider it a Regression Bug.

Impact on development:

The whole point of having the "ComputeWithForm" option is so that you can quickly take advantage of existing functionality while still using XPages to create a new way of accessing existing applications. This regression bug means that the existing application must be modified in order for the new XPages interface to be successfully used -- or else the entirety of the business logic for the page must be re-created on the XPage itself. Recreating the business logic is time consuming and is prone to creating differences in the result when the XPage is used vs. the traditional application.

In addition, this impacted me directly as I had to spend a couple of days chasing down a problem while trying to get used to working in XPages, instead of actually doing productive work.

There are  - loading -  comments....

re: XPages bug - computewithform option for data sources with some formula language commandsBy Karsten Lehmann on 03/01/2012 at 05:22 PM EST
I never understood the computeWithForm command, even in pure backend Java
coding. Our Notes forms don't have many formulas for field computation, almost
all logic is extracted into Lotusscript libraries. And computeWithForm does
only work with formula language AFAIK. Are there many developers out there
still using formula code that much and no Lotusscript? From my experience, even
if you start small with a few lines of formula language, things soon get more
complicated and the code grows until everything is really messed up (like
calculating calendar weeks in formula). Same with XSLT. Nice for small things,
but with growing requirements you either produce a big mess or throw away
everything and start from scratch in Java or Lotusscript.
re: XPages bug - computewithform option for data sources with some formula language commandsBy Andrew Pollack on 03/01/2012 at 05:31 PM EST
I would say the opposite is true.

When I see an app that has a bunch of fields with no formula and all the
business logic is in referenced lotuscript files, I know I"m dealing with
someone who was somewhat late to the Notes game and is applying classical
programming style or even application scripting like from excel to the problem.

Formula language is extremely powerful, very fast, and in many cases makes much
more sense to use than all abstracted logic. We could spend time talking
about this in and of itself, but essentially its the difference between
creating a Notes application, and creating a Lotuscript application that
happens to use Notes to store data. The two are very different.

In any case, the vast majority of apps out there contain computed fields --
often hidden computed fields -- that contain control logic for workflow and
security and whatnot. The purpose of the computewithform functionality was
to allow an xpage to be created without losing all that logic.
re: XPages bug - computewithform option for data sources with some formula language commandsBy Nathan T. Freeman on 03/02/2012 at 09:11 AM EST
Thanks for finding and reporting the exact formula that triggers this failure,
Andrew. I've heard of others running into the same problem, and the only
response has been "don't use computeWithForm." It will be helpful to now point
to a specific function to look for in the future. (Until IBM fixes the obvious
bug, at least.)
re: XPages bug - computewithform option for data sources with some formula language commandsBy Andrew Pollack on 03/02/2012 at 09:47 AM EST
Sure thing.

To me, the ability to use ComputeWithForm as part of retrofitting existing apps
with xpages functionality is too valuable to just ignore the feature.

I suspect there will be other formula functions that cause the same failure in
the same way, though.

Once you have the "Display Errors" control on the page, it makes finding them a
matter of figuring out which field is causing the error and then which function
in that field it is. That's something ANY domino developer has (unfortunately)
been through many times.

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