Tutorials Support > Tutorials? > ProcessingOrder

In developing advanced ZAP forms, it is important to keep in mind the processing order. When a form is submitted, all POST values are appended to the end of the field array *after* the SESSION values. So in the two code examples below, you get different and perhaps unexpected results.

(:zapform:)
(:input text buddieslist "+{$AuthId}" size=30:)
(:zap savedata="buddieslist":)
(:input submit value="Add Me":)
(:zapend:)

Normally you would expect this to execute the list command (which adds the user to the existing list) then save the full list. However "buddieslist" is a POST value so it appears in the field array after the savedata field--which is a SESSION value. In the above snippet, ZAP hits savedata first, saves "+Member" and then the "buddieslist" you want is created after--too late! This form could be fixed by doing something like the following

(:zapform:)
(:input text postbuddieslist "+{$AuthId}" size=30:)
(:zap buddieslist="{postbuddieslist}":)
(:zap savedata="buddieslist":)
(:input submit value="Add Me":)
(:zapend:)

Here, "buddieslist" is executed first, drawing its value from the post value "friends", creating the "buddies" item, and then saving the two fields. Just what you want!

Recap
To recap, here's a summary of the processing order used by the ZAP engine:

1. ZAP input fields are processed, in order
2. POST values are processed, in order

Several times I have forgotten this processing order rule and it has caused me many headaches! Hopefully this tutorial will save you one or two of your own...