XPath expression to select a node if attribute matches, or a node without this attribute otherwise

Question

Considering the following XML

<xml>
  <tag/>
  <tag version="2.1"/>
</xml>

I want an XPath 1.0 expression that returns <tag version="2.1"/> if I search for version 2.1, and <tag/> if I search for version 2.2.

So far, I've tried

/xml/tag[@version = '%version%' or not(@version)]

where %version% is a string that can be either 2.1 or 2.2, but if %version% is 2.1, it returns both nodes.

Searching on 2.1 returns both, because in your xpath you do or not(@version) and that will result in the tag without the attribute. So it does not matter what you pass into %version%, because always <tag/> will be returned because of the or statement... What you are trying to achieve is not possible in one XPath statement. Should be solved in code — Mark Veenstra
– Mark Veenstra, Commented Oct 4, 2013 at 12:31

paul trmbrth · Accepted Answer · 2013-10-04 12:55:00Z

3

You can use something like this, using | (or)

    /xml[not(tag[@version="2.1"])]/tag[not(@version)] |
    /xml[tag[@version="2.1"]]/tag[@version="2.1"]

either xml doesn't have tags with version="2.1", then return tags with no version attribute
or, if xml does contain tags with version="2.1", return these

So that would be in your case

    /xml[not(tag[@version='%version%'])]
        /tag[not(@version)]
    |
    /xml[tag[@version='%version%']]
        /tag[@version='%version%']

answered Oct 4, 2013 at 12:55

paul trmbrth

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Comments

Jirka Š. · Accepted Answer · 2013-10-04 13:08:06Z

3

As xpath 2.0 (if relevant) alternative to very nice @paul answer you could use

if (/xml/tag[@version = '2.1']) then /xml/tag[@version = '2.1'] else /xml/tag[not(@version)]

resp.

if (/xml/tag[@version = '%version%']) then /xml/tag[@version = '%version'] else /xml/tag[not(@version)]

answered Oct 4, 2013 at 13:08

Jirka Š.

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That's indeed a very nice alternative, unfortunately I can't use xpath 2.0. I've updated my question accordingly.