Beware of single character variables in form triggers that log changes

I'm going to describe something which isn't a bug in the strict sense of the word, but will cause Priority to act in a way that we don't want and is unexpected.

There is code in almost every screen to record changes; frequently, there are fields in the screen for which changes are not logged and so we have to add them to our own screen triggers, using the same mechanism for storing the changes. There is a table called GEN_CHANGE_LOG which holds data about changes for most screens and there is a standard procedure for entering data into this table (#INCLUDE TRANSORDER_p/BUF2-CH).

Now down to specifics: I added code a few years ago to the PARTPARAM screen to record changes in the default warehouse of the part using the above procedure. The original value of the field being checked is stored in a variable called OLDVALUE and the new value is stored in - you guessed it - NEWVALUE. As the name of the trigger came after the standard POST-UPDATE-CH trigger, my code executed after the standard code. This shouldn't be a problem as the order of checking should make no difference.

But unfortunately it does. I noticed in the changes log for a few parts that the default warehouse had been changed from 'M' to 'M'. How could this be, when the warehouse names are something like M271 or M504? Why was the trigger storing only one character when the field itself has four characters? I looked at the standard trigger and noted that it was saving the value of a field that could be either Y or empty. Priority handles single character strings in a different manner from longer strings; this gave me the clue that somehow the standard trigger was defining the length of OLDVALUE and NEWVALUE to be single character strings, so that when my trigger executed, only the first character of the value would be stored.

There's no way of redefining the length of a string (AFAIK) in Priority, so I had to look at the problem with some lateral thinking. The solution was to change the name of my trigger so that it executed before the standard trigger. I implemented this and checked: lo and behold! Now warehouse names are being stored in their entirety and are not truncated.

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I wrote the above a few years ago. Today I ran into a similar case: changing the process of a part to Issue in the PART form caused the error log to show that the new process is 'I'. The previous change in the log was changing the type from O to I - that's where the 'single character variable' comes from.

Edit: this bug appears to have been fixed in later versions of Priority; it's certainly fixed in version 21.