[jboss-jira] [JBoss JIRA] Resolved: (BPEL-272) allow xpath expression/query to create more than one occurrence of an element

[Alejandro Guizar (JIRA)]

     [ http://jira.jboss.com/jira/browse/BPEL-272?page=all ]

Alejandro Guizar resolved BPEL-272.
-----------------------------------

    Resolution: Partially Completed

The "last plus one" predicate proposal is already implemented and works for the time being. I will mark this issue as partially completed and revisit the extension assign operation proposal in a future release.

> allow xpath expression/query to create more than one occurrence of an element
> -----------------------------------------------------------------------------
>
>                 Key: BPEL-272
>                 URL: http://jira.jboss.com/jira/browse/BPEL-272
>             Project: JBoss jBPM BPEL
>          Issue Type: Feature Request
>      Security Level: Public(Everyone can see) 
>          Components: Engine
>    Affects Versions: jBPM BPEL 1.1 beta 3
>            Reporter: Alejandro Guizar
>         Assigned To: Alejandro Guizar
>            Priority: Critical
>             Fix For: jBPM BPEL 1.1 GA
>
>
> PROBLEM The current XPath sublanguage implementation automatically creates nodes missing from location paths during assignment. This facility has a number of conceptual limitations. One of them is the inability to append a child element to an existing element if the latter already has a child element with the same name. There is no XPath syntax to express that a new element is required!
> It is tempting to think of a numeric XPath predicate as an array index, leading to the next snippet:
> <copy>
>  <from><literal>haha</literal></from>
>  <to variable='laughter' xmlns:ex='http://jbpm.org/bpel/examples'>
>   <query>ex:laugh[last() + 1]</query>
>  </to>
> </copy>
> However, such an interpretation of a predicate is wrong. Consider the following extract from XPath 1.0 specification on predicates:
> "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."
> The description of the last() function reads:
> "The last function returns a number equal to the context size from the expression evaluation context."
> Noticed the problem? The context position is never greater than the context size. Therefore the predicate [last() + 1] does not represent the position "one past the context size" but the boolean value false. Unfortunately, no other predicate seems appropriate. 
> PROPOSAL Introduce a minor deviation from the XPath 1.0 specification. Interpret the result of a numeric predicate that equals the context size plus one as a  request to create a new occurrence of the node.

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