That looks like normal, if confusing, behavior to me. XPath defines position()
as a dynamic context function, so its meaning can change during evaluation.
http://www.w3.org/TR/xpath20/#id-xp-evaluation-context-components
http://www.w3.org/TR/xpath20/#dt-dynamic-context
I think this is the most relevant bit:
> The context position is the position of the context item within the sequence
> of items currently being processed.] It changes whenever the context item
> changes. When the focus is defined, the value of the context position is an
> integer greater than zero. The context position is returned by the expression
> fn:position(). When an expression E1/E2 or E1[E2] is evaluated, the context
> position in the inner focus for an evaluation of E2 is the position of the
> context item in the sequence obtained by evaluating E1. The position of the
> first item in a sequence is always 1 (one). The context position is always
> less than or equal to the context size.
After [exists(*)] has been evaluated, [1] sees every document-node() in
collection('test')[*] as its own input sequence. Therefore every document has
position() = 1. So the behavior is confusing, but correct.
What you probably want is:
(collection(test)[*])[1]
The extra parens change the scope of the [1] predicate.
-- Mike
On 22 Jan 2013, at 08:44 , Stéphane TOUSSAINT <[email protected]>
wrote:
> Hi,
>
> I just found something wrong (I guess) with XPath predicates on ML 6.0-2.1
>
> The following query returns weird result :
>
> fn:count(for $doc in fn:collection("test")[fn:exists(*)][1]
> return $doc)
>
> Say I put 10 documents in collection "test", I guess this query return only 1
> (the first document) document from the collection. But instead it returns 10
> documents.
> I seems that after the first predicates there is 10 sequences of 1 document
> each instead of one single collection with 10 document inside.
>
> For information, this is the minimal test case I was able to write, but it is
> the same with more complexe predicates.
>
> Note that
>
> for $doc in fn:collection("test")[1]
> return $doc
>
> successfully return one single element.
>
> Any clue? thanks
>
> Stéphane
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