Question

如何从这家书店归还第三本书？

declare context item := document{
<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>
};

let $date := current-date()
for $ctx in context
return $ctx/bookstore/book[3]

到目前为止，我只是得到一个空白的结果：

PS C：\ Users \ thufir \ Desktop \ basex> PS C：\ Users \ thufir \ Desktop \ basex> basex contextDoc.xq PS C：\ Users \ thufir \ Desktop \ basex>

Answer 1

您需要调整 for 子句，并使用点表示法引用上下文，如下所示：

XQuery

declare context item := document {
<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>
};

for $ctx in ./bookstore/book[3]
return $ctx

输出

<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>

Answer 2

您的问题标题说的是“使用FLWOR表达式”，但是FLWOR表达式对于这样一个简单的查询来说是过大的。

@YitzhakKhabinsky提供了正确的答案：

for $ctx in ./bookstore/book[3] return $ctx

但是表达式for $X in Y return $X只是Y的冗长表达，因此简化为

./bookstore/book[3]

或更简单

bookstore/book[3]

Answer 3

当您从for循环中进行迭代时，您会在$ ctx变量中获得元素书店。您可以通过写名称（$ ctx）进行检查。因此，您无需再次将bookstore元素写为$ ctx / bookstore / book [3]。只需从代码中删除书店，然后将查询写为$ ctx / book [3]。

Answer 4

只是改变

for $ctx in context

到

for $ctx in .

请参见https://xqueryfiddle.liberty-development.net/b4GWVn

如何在XQuery中使用FLOWR从这家书店归还第三本书？

4 个答案: