Tuesday, 5 January 2010

Passing parameters to an XSLT in BPEL

Yesterday for me it became handy to be able to pass parameters to an XSLT in BPEL. I've seen the need earlier, but solved it a different way. By setting the target element with a default and then over writing that default in a later assign-copy step.

But yesterday I had to transform a document a variable number of times, for a list of elements. In my case I had a document with a list of recipients and I had to transform that to another document for each recipient. Each recipient had a number of elements with personal and address information that had to be transformed to the target. So simply defaulting and overwriting would not work, or was a lot of work.

To pass parameters as arguments to a XSLT is quite easy and neatly described in several blogs, amongst others in Sudheer Dhurjati's Blog.

In my case I had to pass an index to be able to select the particular recipient that I need to transform. And another parameter that holds a number of documents that is determined from another source:
<?xml version="1.0" encoding="UTF-8" ?>
<parameters xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://schemas.oracle.com/service/bpel/common /S:/DEV/Sources/BPEL/Processes/CRMI_COM_VersturenBerichtContactMgt/1.0/src/xsltparameters.xsd"

In Sudheer's blog (and in other examples) the parameters are initialized by copying an XML fragment with the particular parameters. If you have to change one of the parameters this could be done by doing an indexed xpath-expression in the <to> of the assign step:
with [http://schemas.oracle.com/service/bpel/common] as [prm]
<value xmlns="http://schemas.oracle.com/service/bpel/common">1</value>

But for flexibilities sake, I would propose a slightly different approach. And for that I need an adapted version of the XSD:
<?xml version="1.0" encoding="windows-1252" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
<xsd:element name="parameters">
<xsd:element ref="bplcmn:item" minOccurs="1" maxOccurs="unbounded"/>
<xsd:element name="item" type="bplcmn:itemType"/>
<xsd:complexType name="itemType">
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="value" type="xsd:string"/>

In this XSD I created 'item' as a seperate element based on a seperated (named) complex-type. I'm actually not so fond of nested complex-types, because it prevents you from using elements lower in the hierarchy for seperate variables.
Using this XSD, you can create a seperate item-variable, based on the item-element.
This is item-variable can be filled with a name and value, just by copying to the particular elements.
The item variable has then to be added to the parameters node using the addChildNode function:
The first argument of the addChildNode function denotes the element under which you want to add a child. In the expression above this is the 'parameters' element in the XsltParams variable. The second argument is the node you want to add as a child, in this case the 'item'-variable. Of course this expression is the <from>-expression in the copy-rule of the assignment step. The <to> will be most of the times the parent element used in the addChildNode expression:
<to variable="XsltParams" query="/bplcmn:parameters"/>
I found the description of the addChildNode function in the expression builder not so clear. So this might also be helpfull for other situations where you have to build up a node structure dynamically.

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