How to deal with empty node in xquery?

Question

I want to print a TSV output like this. But when $x/span does not find anything, there will be only two columns printed. How to insert an empty field in the 2nd column when $x/span finds nothing? Thanks.

for $x in //td/b/a[@title]/parent::b/parent::td
return join(
    (
        $x/b/a/@title
        , $x/span
        , $x/p
    )
    , x:cps(9)
)

Please share two things: (1) your input XML, and (2) desired output. — Yitzhak Khabinsky, Jul 26 '20 at 01:35
What does the join() function do? It's not a standard XQuery function. — Michael Kay, Jul 26 '20 at 08:43
@MichaelKay http://www.benibela.de/documentation/internettools/xpath-functions.html#x-join — Reino, Jul 26 '20 at 09:50
@user1424739 An XPath expression would be enough in this case. You could simplify it to: `-e '//td[b/a[@title]]/join((b/a/@title,(span,"")[1],p),x:cps(9))'`. — Reino, Jul 26 '20 at 12:13
@Reino OK. This is even better. Could you post it as an answer so that I can accept it? — user1424739, Jul 26 '20 at 13:57

score 2 · Accepted Answer · answered Jul 26 '20 at 18:40

2

XPath:

//td[b/a[@title]]/join(
  (
    b/a/@title,
    (span,"")[1],
    p
  ),
  x:cps(9)
)

XQuery:

for $x in //td[b/a[@title]] return
$x/join(
  (
    b/a/@title,
    (span,"")[1],
    p
  ),
  "&#9;"
)

answered Jul 26 '20 at 18:40

Reino

3,203
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score 1 · Answer 2 · answered Jul 26 '20 at 02:29

1

You can use if/else statement to control what to do in case of the missing span tag.

if (empty($x/span)) then  
    (: do what you need here :)
else  
    $x/span

answered Jul 26 '20 at 02:29

Yitzhak Khabinsky

18,471
2
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21

I don’t want to rewrite the whole join statement. Is there a way to assign the middle column value to a variable depending on whether $x/span is empty or not? – user1424739 Jul 26 '20 at 04:14
@user1424739, you don't need to rewrite the entire `join` statement. Just replace the `$x/span` with the expression I showed. – Yitzhak Khabinsky Jul 26 '20 at 04:21

score 1 · Answer 3 · answered Jul 26 '20 at 08:45

1

A common idiom for this is

($x/span, "default")[1]

But this might not be right for you if $x/span can select multiple items.

answered Jul 26 '20 at 08:45

Michael Kay

156,231
11
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164

For my case, $x/span can return either 0 or 1 element. So this works for my case. And this solution is more succinct than the solution by @YitzhakKhabinsky. So I'd consider this solution is better. – user1424739 Jul 26 '20 at 11:06

How to deal with empty node in xquery?

3 Answers3