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https://issues.apache.org/jira/browse/JXPATH-163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13886230#comment-13886230
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Michele Vivoda edited comment on JXPATH-163 at 1/30/14 4:02 AM:
----------------------------------------------------------------
Hi,
>From XPath specification:
http://www.w3.org/TR/xpath/#NT-PredicateExpr
[8] Predicate ::= '[' PredicateExpr ']'
[9] PredicateExpr ::= Expr
A predicate filters a node-set with respect to an axis to produce a new
node-set. For each node in the node-set to be filtered, the PredicateExpr is
evaluated with that node as the context node, with the number of nodes in the
node-set as the context size, and with the proximity position of the node in
the node-set with respect to the axis as the context position; if PredicateExpr
evaluates to true for that node, the node is included in the new node-set;
otherwise, it is not included.
A PredicateExpr is evaluated by evaluating the Expr and converting the result
to a boolean. If the result is a number, the result will be converted to true
if the number is equal to the context position and will be converted to false
otherwise; if the result is not a number, then the result will be converted as
if by a call to the boolean function. Thus a location path para[3] is
equivalent to para[position()=3].
--------------
I read that if the Expr is a string, it is converted to true if the string is
not empty, meaning 'any node' and so the first node is selected, if it were a
"node set" selection instead of a "single node" then all nodes would have been
selected. JXPath seems to comply with the spec.
You may probably consider to use number() to force conversion to a number that
then is checked against the position.
/se:someArray[number($var)]
or also in this way:
/se:someArray[position() = $var]
was (Author: vivodamich...@hotmail.com):
Hi,
>From XPath specification:
http://www.w3.org/TR/xpath/#NT-PredicateExpr
[8] Predicate ::= '[' PredicateExpr ']'
[9] PredicateExpr ::= Expr
A predicate filters a node-set with respect to an axis to produce a new
node-set. For each node in the node-set to be filtered, the PredicateExpr is
evaluated with that node as the context node, with the number of nodes in the
node-set as the context size, and with the proximity position of the node in
the node-set with respect to the axis as the context position; if PredicateExpr
evaluates to true for that node, the node is included in the new node-set;
otherwise, it is not included.
A PredicateExpr is evaluated by evaluating the Expr and converting the result
to a boolean. If the result is a number, the result will be converted to true
if the number is equal to the context position and will be converted to false
otherwise; if the result is not a number, then the result will be converted as
if by a call to the boolean function. Thus a location path para[3] is
equivalent to para[position()=3].
--------------
I read that if the Expr is a string, it is converted to true if the string is
not empty, meaning 'any node' and so the first node is selected, if it were a
"node set" selection instead of a "single node" then all nodes would have been
selected. JXPath seems to comply with the spec.
You may probably consider to use number() to force conversion to a number that
then is checked against the position.
/se:someArray[number($var)]
> String variables cannot be used as indices
> ------------------------------------------
>
> Key: JXPATH-163
> URL: https://issues.apache.org/jira/browse/JXPATH-163
> Project: Commons JXPath
> Issue Type: Bug
> Affects Versions: 1.3
> Reporter: Alexander Koledzhikov
> Priority: Minor
> Attachments: commons-jxpath.patch
>
>
> If I have a string variable, I cannot use it as an index in an xpath query.
> For example, if var = "5", this query will return the 1st element, not the
> fifth:
> /se:someArray[$var]
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