XPath select based on child value(s)

Question

Here's some xml:

<books>
    <book>
        <author>Tom</author>
        <genres>
            <genre>Science</genre>
            <genre>Romance</genre>
        </genres>
    </book>
    <book>
        <author>Mike</author>
        <genres>
            <genre>Politics</genre>
            <genre>Romance</genre>
        </genres>
    </book>
</books>

How can I define an xpath such that it pulls all Romance books? Or maybe all Romance and Politics books?

Rubens Farias · Accepted Answer · 2016-12-08T13:45:57.107

13

You can go with //book[./genres/genre = 'Romance'] and //book[./genres/genre = 'Romance' and ./genres/genre = 'Politics'], respectively

edited Dec 08 '16 at 13:45

answered Dec 07 '16 at 20:52

Rubens Farias

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I actually tried this exactly but it didn't return results. I am probably missing something somewhere. I'll play some more. – Jon Glazer Dec 08 '16 at 13:25
2

@jglazer Does your actual XML document look exactly like the one you show above, or did you perhaps omit something or simplify it? Rubens, `./` in the predicates is not necessary, `child::` is implicitly assumed as the context. – Mathias Müller Dec 08 '16 at 13:38
2

@jglazer: This answer is correct (+1), only slightly more verbose than necessary (as Mathias mentioned). I've added some [**XPath troubleshooting steps**](http://stackoverflow.com/a/41030788/290085) to my answer -- hopefully those will help. – kjhughes Dec 08 '16 at 13:41
Thanks kjhughes etc.... I Won't be able to play with it until next week but I'll give it more effort. – Jon Glazer Dec 10 '16 at 16:49

kjhughes · Answer 2 · 2020-06-30T11:50:14.047

All books in Romance genre:

//book[genres/genre = 'Romance']

All books in Romance and Politics genre:

//book[genres/genre = 'Romance' and genres/genre = 'Politics']

All books in Romance that are also in Politics genre (same as and above):

//book[genres/genre = 'Romance'][genres/genre = 'Politics']

All books in Romance or Politics genre:

//book[genres/genre = 'Romance' or genres/genre = 'Politics']

All books in Romance or Politics genre (XPath 2.0 only):

//book[genres/genre = ('Romance', 'Politics')]

Notes:

//book finds all book elements anywhere beneath the root element; /books/book finds all book children of the books root element. For the given XML, they select the same elements.
You can append /author to any of the above XPaths to select the author elements of the books of the specified criteria.

Having trouble making it work?

First, establish that a basic XPath works: //book should return two elements.

If it does not:

Check spelling carefully of both the XPath expression and the XML.
Check case. XML and XPath are case sensitive.
Check that no namespaces are in play. Namespaces are effectively a part of the names of elements and attributes and must be accounted for. See How does XPath deal with XML namespaces?

Then, incrementally add XPath steps from there:

//book[genres] should select book elements with any genres child element.
//book[genres/genre] should select book elements with any genres child element, only if it in turn has a genre child element.
//book[genres/genre = 'Romance'] should select all books in Romance genre, as requested. Note that 'Romance' must be quoted; otherwise, the expression would be testing against the string value of a Romance child element of book and will certainly fail.

XPath select based on child value(s)

2 Answers2

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