There are two ways to extend a pipeline defined for a PipelineManager. One is to copy the entire XML file into your CONFIG layer and make the necessary changes. The other way is to use XML combination. Using XML combination is the preferred approach. The example below demonstrates of how to use XML combination to modify a pipeline chain.

The XML below is a section of the processOrder pipeline chain as it appears out of the box.

<pipelinechain name="processOrder" transaction="TX_REQUIRED"
           headlink="executeValidateForCheckoutChain">
  <pipelinelink name="executeValidateForCheckoutChain" transaction="TX_MANDATORY">
     <processor
            jndi="/atg/commerce/order/processor/ExecuteValidateForCheckoutChain"/>
     <transition returnvalue="1" link="checkForExpiredPromotions"/>
  </pipelinelink>
  <pipelinelink name="checkForExpiredPromotions" transaction="TX_MANDATORY">
     <processor jndi="/atg/commerce/order/processor/CheckForExpiredPromotions"/>
     <transition returnvalue="1" link="removeEmptyShippingGroups"/>
</pipelinelink>

The following example demonstrates how to add a new processor called purgeExcessOrderData between the executeValidateForCheckoutChain and checkForExpiredPromotions processors in the processOrder pipeline chain. The following XML code should be added to your config layer.

The important sections of this code are the additions of the xml-combine attributes in the pipelinechain and pipelinelink tags. The pipelinechain tag indicates what is being appended to its contents. The pipelinelink tag for executeValidateForCheckoutChain indicates what is replacing its contents.

<pipelinemanager>
 <pipelinechain name="processOrder" transaction="TX_REQUIRED"
            headlink="executeValidateForCheckoutChain" xml-combine="append">
   <pipelinelink name="executeValidateForCheckoutChain" transaction="TX_MANDATORY"
         xml-combine="replace">
     <processor
           jndi="/atg/commerce/order/processor/ExecuteValidateForCheckoutChain"/>
     <transition returnvalue="1" link="purgeExcessOrderData"/>
   </pipelinelink>
   <pipelinelink name="purgeExcessOrderData" transaction="TX_MANDATORY">
     <processor jndi="/atg/commerce/order/processor/PurgeExcessOrderData"/>
     <transition returnvalue="1" link="checkForExpiredPromotions"/>
   </pipelinelink>
 </pipelinechain>
</pipelinemanager>

The purgeExcessOrderData processor’s transition is what the executeValidateForCheckoutChain transition is in the base file within the Core Platform.