nested looping within Xquery results in a mismatch? and idioms

问题

I'm playing with the bookstore XML from w3schools:

<bookstore>

<book category="cooking">
  <title lang="en">Everyday Italian</title>
  <author>Giada De Laurentiis</author>
  <year>2005</year>
  <price>30.00</price>
</book>

<book category="children">
  <title lang="en">Harry Potter</title>
  <author>J K. Rowling</author>
  <year>2005</year>
  <price>29.99</price>
</book>

<book category="web">
  <title lang="en">XQuery Kick Start</title>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
  <year>2003</year>
  <price>49.99</price>
</book>

<book category="web" cover="paperback">
  <title lang="en">Learning XML</title>
  <author>Erik T. Ray</author>
  <year>2003</year>
  <price>39.95</price>
</book>

</bookstore>

which I query of using XQuery 3.1:

xquery version "3.1";

declare option output:method 'xml';

for $doc in db:open("bookstore")
let $books := $doc/bookstore/book
return(
    for $book in $books
    let $authors := $book/author
    let $title := data($book/title)
    return
    <b>{
    (<t>{$title}</t>,$authors)
    }</b>
)

The output, so far as it goes, is the desired result.

the nested for loop of the query is comprehensible, but perhaps not "Xquery"-ish?

That a book has, at least for this example, a single title and yet multiple authors, creates, perhaps a bit of a mismatch insofar as the loop here is being used or misused.

output:

<b>
  <t>Everyday Italian</t>
  <author>Giada De Laurentiis</author>
</b>
<b>
  <t>Harry Potter</t>
  <author>J K. Rowling</author>
</b>
<b>
  <t>XQuery Kick Start</t>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
</b>
<b>
  <t>Learning XML</t>
  <author>Erik T. Ray</author>
</b>

This question is not meant to be a code-review per se, more looking for alternate or more standard approaches. A not entirely unrelated tangent for context:

https://martinfowler.com/bliki/OrmHate.html

回答1:

I'm not sure what your question is, to be honest, but your XQuery can be simplified quite a bit

for $book in db:open("bookstore")/bookstore/book
return <b>
  <t>{string($book/title)}</t>
  {$book/author}
</b>

which results in the same nodes being created

<b>
  <t>Everyday Italian</t>
  <author>Giada De Laurentiis</author>
</b>
<b>
  <t>Harry Potter</t>
  <author>J K. Rowling</author>
</b>
<b>
  <t>XQuery Kick Start</t>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
</b>
<b>
  <t>Learning XML</t>
  <author>Erik T. Ray</author>
</b>

来源：https://stackoverflow.com/questions/65275437/nested-looping-within-xquery-results-in-a-mismatch-and-idioms

标签

xml

xpath

xquery

nested-loops

flwor