Hi Eddie
Thanks for that. I guess thats my question; should the 'root' be the context
node on which the XPath expression evaluates or should 'root' always be the
document? (Lets not worry about document fragments for this discussion)
I always thought it should be the document, otherwise the use of "/" at the
start of an expression adds no extra value. Lets take an example.
<foo c="123">
<bar>
<x>
<y>hello</y>
</x>
</bar>
</foo>
Lets say we get access to the <bar> element. (Using dom4j code for a
second).
Node bar = document.selectSingleNode( "/foo/bar" );
Now typically if I wanted to navigate relative to the <bar> element I'd just
use a relative XPath expression which does not start with "/".
Node y = bar.selectSingleNode( "x/y" );
There's no need for me to start the expression with "/" since the XPath
expression will start from <bar> anyway as its relative.
However if I wanted to get access to the c attribute, I could do
Node c = bar.selectSingleNode( "/@c" );
Couldn't I?
i.e. the addition of "/" to the front of the XPath expression means use the
document as the root, not the node I happen to be evaluating the expression
on, which is <bar>. If the "/" means use the evaluation context as the root
then there is no difference between "/@c" and "@c" which would seem pretty
pointless to me.
Is my understanding correct here? There does seem to be a bit of confusion
on this topic.
James
----- Original Message -----
From: "Eddie" <[EMAIL PROTECTED]>
To: "James Strachan" <[EMAIL PROTECTED]>
Sent: Tuesday, November 20, 2001 10:02 AM
Subject: Re: [Jaxen] Paths beginning with / should start from document?
> James,
> if an XPath starts with a "/" then it is an absolute path and is taken as
> meaning the root node. The "root" is usually the Document node but doesn't
> necessarily need to be. It could be just the root of a particular branch.
> The root is defined by the context that you set before evaluation using
the
> method Context.setNodeSet(List nodeSet). I'm not sure what is supposed to
> happen if you have no root but several top level nodes. You probably get
an
> exception or an empty result set.
> Hope this helps
> Eddie
>
>
> ----- Original Message -----
> From: "James Strachan" <[EMAIL PROTECTED]>
> To: "Jaxen-Interest" <[EMAIL PROTECTED]>
> Sent: Tuesday, November 20, 2001 9:26 AM
> Subject: [Jaxen] Paths beginning with / should start from document?
>
>
> > Just a quick clarifcation that I wanted to double check with the list.
Any
> > XPath expression that starts with "/" should always start from the
> document
> > of the node on which the XPath is evaluated, shouldn't it?
> >
> > i.e. the behaviour is like a file system where whatever directory (node)
> you
> > evaluate a path expression, anything starting with "/" starts from the
> root
> > directory (the document).
> >
> > This is true isn't it?
> >
> > James
> >
> >
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