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

[Felipe (JIRA)]

    [ http://jira.jboss.com/jira/browse/BPEL-272?page=comments#action_12371292 ] 
            
Felipe commented on BPEL-272:
-----------------------------

WORKAROUND UNTIL THIS IS FIXED:

Following the oracle approach (cf. supra.), a web service can be used to provide an operation that returns an array of the right size. Operations to add items can be done too. Z.B. creating a lista of size four:

ESQUEMA:
   <complexType name="ListaString">
     <sequence>
       <element name="item" type="xsd:string" minOccurs="1" maxOccurs="unbounded"></element>
     </sequence>
   </complexType>
WSDL:
   <wsdl:message name="obtenerListaStringRequest">
   	<wsdl:part name="obtenerListaStringRequest" type="xsd:int"></wsdl:part>
   </wsdl:message>
   <wsdl:message name="obtenerListaStringResponse">
   	<wsdl:part name="obtenerListaStringReturn"
   		type="tns1:ListaString">
   	</wsdl:part>
   </wsdl:message>
      <wsdl:operation name="obtenerListaString">
      	<wsdl:documentation>Este método fue añadido para corregir las deficiencias del bpel en la creación de secuencias. Cf. http://jira.jboss.com/jira/browse/BPEL-272</wsdl:documentation>
      	<wsdl:input message="impl:obtenerListaStringRequest" name="listaStringPedir"></wsdl:input>
      	<wsdl:output message="impl:obtenerListaStringResponse" name="listaStringDevolver"></wsdl:output>
      </wsdl:operation>
BPEL:
<variable name="listacadenas" messageType="BAncha:obtenerListaStringResponse" />
    <variable name="entero" messageType="BAncha:obtenerListaStringRequest"/>
<assign>
  	<copy>
  		<from expression="4"/>
  		<to variable="entero" part="obtenerListaStringRequest"/>
  	</copy>
  </assign>
    <invoke partnerLink="BaPartnerLink" portType="BA:Bara"
              operation="obtenerListaString" inputVariable="entero"
              outputVariable="listacadenas"/>

  Haleeee

> 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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