[英]BaseX XQuery No context item defined to evaluate 'root()'
我正在BaseX
上尝试此XQuery
:
xquery //Bookstore/Book/Title
Error:
Stopped at ., 1/2:
[XPDY0002] No context item defined to evaluate 'root()'.
Compiling:
- simplifying descendant-or-self step(s)
Query:
//Bookstore/Book/Title
Optimized Query:
root()/descendant::Bookstore/Book/Title
Query plan:
<QueryPlan>
<CachedPath>
<Root/>
<IterStep axis="descendant" test="Bookstore"/>
<IterStep axis="child" test="Book"/>
<IterStep axis="child" test="Title"/>
</CachedPath>
</QueryPlan>
我已经上网搜索了,但我真的不知道该怎么办。 为什么会发生这种情况,因为我在命令中有root element
,即Bookstore
。 我正在尝试查询此:
<Bookstore>
<Book ISBN="ISBN-0-13-713526-2" Price="85" Edition="3rd">
<Title>A First Course in Database Systems</Title>
<Authors>
<Author>
<First_Name>Jeffrey</First_Name>
<Last_Name>Ullman</Last_Name>
</Author>
<Author>
<First_Name>Jennifer</First_Name>
<Last_Name>Widom</Last_Name>
</Author>
</Authors>
</Book>
<Book ISBN="ISBN-0-13-815504-6" Price="100">
<Title>Database Systems: The Complete Book</Title>
<Authors>
<Author>
<First_Name>Hector</First_Name>
<Last_Name>Garcia-Molina</Last_Name>
</Author>
<Author>
<First_Name>Jeffrey</First_Name>
<Last_Name>Ullman</Last_Name>
</Author>
<Author>
<First_Name>Jennifer</First_Name>
<Last_Name>Widom</Last_Name>
</Author>
</Authors>
<Remark>
Buy this book bundled with "A First Course" - a great deal!</Remark>
</Book>
<Book ISBN = "ISBN-0-11-222222-3" Price="50">
<Title>Jennifer's Economical Database Hints</Title>
<Authors>
<Author>
<First_Name>Jennifer</First_Name>
<Last_Name>Widom</Last_Name>
</Author>
</Authors>
</Book>
<Magazine Month="January" Year="2009">
<Title>National Geographic</Title>
</Magazine>
<Magazine Month="February" Year="2009">
<Title>National Geographic</Title>
</Magazine>
<Magazine Month="February" Year="2009">
<Title>Newsweek</Title>
</Magazine>
</Bookstore>
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