Question

If say I’ve got the following XML file:

<title text=“title1">
    <comment id=“comment1">
        <data> this is part of comment one</data>
        <data> this is some more of comment one</data>
    </comment>
    <comment id=“comment2”>
        <data> this is part of comment two</data>
        <data> this is some more of comment two</data>
        <data> this is even some more of comment two</data>
    </comment>
</title>

And I’m given the following XPath query:

/title/comment/@id

What would be the best way to get the subtree to which the expression belongs.

So for instance, the above expression would return:

• id="comment1"
• id="comment2"

To which, comment1 belongs to subtree:

    <comment id="comment1">
        <data> this is part of comment one</data>
        <data> this is some more of comment one</data>
    </comment>

And, comment2 belongs to subtree:

    <comment id=“comment2">
        <data> this is part of comment two</data>
        <data> this is some more of comment two</data>
        <data> this is even some more of comment two</data>
    </comment>

The reason I want this is so that I can recursively make a call on the sub-tree where the Xpath expression is resolved to.

I am coding this in Java using DOM.

Answer 1

It sounds like the XPath expression is unknown until run time.
And you want to obtain the parent of each node selected by the XPath expression… is that right? The <comment> element is the parent of each comment/@id attribute. Obtaining the <comment> element is equivalent to obtaining its subtree (descendants), because you can extract its descendants using further XPath expressions or DOM functions, or you can copy the <comment> element with its descendants.

One way to answer your question then is to simply append “/..” to the end of the XPath expression. E.g.

"/title/comment/@id"

would become

"/title/comment/@id/.."

which is equivalent to @Dan’s answer, but can be easily derived from whatever the XPath expression may be.