Here is what happens when a page gets submitted.
First the computations in the page process or middle block of the page gets executed. (After all the computations executed without any errors), then it goes do validations block
If the validations gets executed based on conditions, and if the validations raises an error then the further processing of the page is stopped.
(All the validations are executed first and if none of them raises any errors then it goes to page processes. If any one of the validations raises error or all of them or some of them raises error then it stops further processing of the page.
Once page is submitted here are the sequence or flow of actions and lets make it simple and all are after page submit
If validations are successful then => Page Processes
Branching (If any)
Well that is good to know. But then the question becomes: why does my page give me "Current version of data in database has changed since user initiated update process" when I try to change a field in a detail row? There is no other user updating the same row. I can get out of that invoice detail page altogether. Re-retrieve the invoice number and try the same update and get the same error message. What could possibly cause this error? I am at wits end! I was hoping that it was calculations that I was doing in the processes section and the commit was causing the problem. What about calculations done before ApplyMRU process? Could a calculation before the process be the culprit?
If you apply any dml to the same table that is defined in your multi-row-process BEFORE it executes then you will run into the checksum error. A checksum is generated during page render based on the current values of the fields of the fetched row. When the page submits and it comes to the MRP it will then create a checksum again, based on the current values of the row in the database. If that value matches the one that was generated at page render then the engine knows no changes will be lost or overwritten and it will process the submitted values. Obviously, if you alter values on the row in the database before the process fires, then the checksum it will generate will differ from the submitted one, causing a checksum error.
Yes, I have reviewed where I am doing the calculations and it is AFTER the ApplyMRU and ApplyMRD processes. This is so frustrating! But the calculations update totals in the Invoice Table. My Master/Detail is based on the Invoice as the Master and then Invoice_Details as the detail portion of the page. If I execute the page process after the APPLYMRU and then want to process something on the same page again, I get the error. It could be that the invoice data is now different because it was not typed in from the form but updated through a background process?