[TAP5-587] Ajax update of volatile Loop in Zone in Form causes issues on Form submit

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Invalid
• Affects Version/s: 5.1.0.0, 5.1.0.1, 5.1.0.2
• Component/s: tapestry-core
• Labels: tapestry5-review-for-closing
• Assignee: Unassigned
• Reporter: Joost Schouten
• Created: 20/Mar/09 05:14
• Updated: 19/Oct/11 16:59
• Resolved: 19/Oct/11 16:59

Description

When a volatile Loop in a form gets updated through Ajax and results in having less source items than on initial page render, a java.util.NoSuchElementException (see below) because the Loop seems to think there are more source items then there are. The whole volatile setting on a loop is kind of unclear to me but I suspect it is intended for a Loop in a form that holds Form Input. In my usecase the Form is just to display non-form data. If my assumption is correct, I miss a parameter on the form like noFormDataLoop, to tell the loop to ignore the complete Loop for state saving.

When I add if(iterator.hasNext()) to the advanceVolatile() method like below, my usecase works again. I am unsure however if this would interfere with other usecases. All unit tests still work which gives me hope this simple solution might be included.

private void advanceVolatile()

{ if(iterator.hasNext()) value = iterator.next(); startHeartbeat(); }

I would love to get some input on if my assumptions are right and if my proposed solutions might work. If so, I'll go ahead and build a patch.

Cheers,
Joost

--------- the exception on Form submit with volatile=true on Loop and Loop item substraction through AJAX --------------

Caused by: java.util.NoSuchElementException
at java.util.AbstractList$Itr.next(AbstractList.java:427)
at org.apache.tapestry5.corelib.components.Loop.advanceVolatile(Loop.java:335)
at org.apache.tapestry5.corelib.components.Loop.access$200(Loop.java:41)
at org.apache.tapestry5.corelib.components.Loop$3.execute(Loop.java:92)
at org.apache.tapestry5.corelib.components.Loop$3.execute(Loop.java:96)
at org.apache.tapestry5.corelib.components.Form.executeStoredActions(Form.java:471)
... 81 more