Error “undefined variable at noteLine” in FLWOR expression when returning multiple nodes

问题

I have a very strange problem with a FLWOR loop, that works one way but not another. The goal is to take a string of any length, and break it into XML nodes that can only hold 80 chars each. So, first whack, this works great:

    for $noteLine in $noteLineArr
    where $noteLine != ''

    return
    if (fn:string-length(fn:normalize-space($noteLine)) < 80) then (
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 1, 80)}</Descr>
    </NTE>  
    ) else if (fn:string-length(fn:normalize-space($noteLine)) > 80 and fn:string-length(fn:normalize-space($noteLine)) <= 160) then (
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 1, 80)}</Descr>
    </NTE>,
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 81, 80)}</Descr>
    </NTE>
    ) else if (fn:string-length(fn:normalize-space($noteLine)) > 160 and fn:string-length(fn:normalize-space($noteLine)) <= 240) then (
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 1, 80)}</Descr>
    </NTE>,
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 81, 80)}</Descr>
    </NTE>,
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 161, 80)}</Descr>
    </NTE>
    ) else()            

So, I get it in my head that this isn't very elegant. I try to clean it up by moving the first element out of the if, since it should always get used, right? Less code that way? So here is what I tried:

for $noteLine in $noteLineArr
where $noteLine != ''

return

    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 1, 80)}</Descr>
    </NTE>, 
    if (fn:string-length(fn:normalize-space($noteLine)) > 80 and fn:string-length(fn:normalize-space($noteLine)) <= 160) then (
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 81, 80)}</Descr>
    </NTE>
    ) else if (fn:string-length(fn:normalize-space($noteLine)) > 160 and fn:string-length(fn:normalize-space($noteLine)) <= 240) then (
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 81, 80)}</Descr>
    </NTE>,
    <NTE>
        <NoteRefCd>WHI</NoteRefCd>
        <Descr>{fn:substring(fn:normalize-space($noteLine), 161, 80)}</Descr>
    </NTE>
    ) else()    

And the parser is now telling me "undefined variable at noteLine" pointing to the first "if" line. What am I missing here? (note that yes, I do have other ideas of how to clean this up even more, but this was the first simple step and when it failed miserably, I panicked).

Solution (thanks to Jens Erat) The return block needs to be wrapped in parentheses in order to force it to evaluate fully on each iteration of the flwor loop. Thusly:

for $noteLine in $noteLineArr
where $noteLine != ''

return
    (
        <NTE>
            <NoteRefCd>WHI</NoteRefCd>
            <Descr>{fn:substring(fn:normalize-space($noteLine), 1, 80)}</Descr>
        </NTE>, 
        if (fn:string-length(fn:normalize-space($noteLine)) > 80 and fn:string-length(fn:normalize-space($noteLine)) <= 160) then (
        <NTE>
            <NoteRefCd>WHI</NoteRefCd>
            <Descr>{fn:substring(fn:normalize-space($noteLine), 81, 80)}</Descr>
        </NTE>
        ) else if (fn:string-length(fn:normalize-space($noteLine)) > 160 and fn:string-length(fn:normalize-space($noteLine)) <= 240) then (
        <NTE>
            <NoteRefCd>WHI</NoteRefCd>
            <Descr>{fn:substring(fn:normalize-space($noteLine), 81, 80)}</Descr>
        </NTE>,
        <NTE>
            <NoteRefCd>WHI</NoteRefCd>
            <Descr>{fn:substring(fn:normalize-space($noteLine), 161, 80)}</Descr>
        </NTE>
        ) else()
    )

回答1:

This is a minor syntax issue. You have to put parenthesis around the elements created in the return clause. To further explain the issue, I'm providing a similar, but simplified example:

for $i in 1 to 3
return
    <foo />,
    <bar />

You'd expect to get following result (the two elements repeated three times):

<foo/>
<bar/>
<foo/>
<bar/>
<foo/>
<bar/>

But instead, you get

<foo/>
<foo/>
<foo/>
<bar/>

This is because the query is actually evaluated as

(
  for $i in 1 to 3
  return
      <foo />
),
<bar />

In your code, you don't get unexpected output, but an error message. This is because $noteLine is not defined after the first comma ,. You would get a similar error message for following query:

for $i in 1 to 3
return
    <foo>{ $i }</foo>,
    <bar>{ $i }</foo>

Here, $i is not bound for the <bar/> element, as the query is evaluated as

(
  for $i in 1 to 3
  return
      <foo>{ $i }</foo>
),
<bar>{ $i }</foo> (: obivously, $i is not defined here :)

来源：https://stackoverflow.com/questions/34935080/error-undefined-variable-at-noteline-in-flwor-expression-when-returning-multip