Why not payloadFactory Mediator ?
If you are familiar with WSO2 ESB you may know that if we want to change the entire payload into a different payload or build a new payload by extracting properties using the existing payload, we can use payloadFactory mediator. But for this requirement that I'm going to describe, payload factory mediator will not be the ideal mediator due to different reasons. One major reason is, if the current payload is bit lengthy one, you will have to build the other parts of the payload even though you don't need to change them at all.
If not payloadFactory then what?
It will be very convenient to get this requirement done using Enrich Mediator. Enrich Mediator will take your desired OMElement (xml element) using the configuration that you state in the source section and then will insert it to the target location you state.
I will explain the configuration using a sample usecase. Say I receive some request into ESB and depending on some properties in the payload I want to set some element in the payload. For an example assume I need to insert a new element into the payload if the received payload is not a valid payload.
In the above example I have set the incoming request to ESB in to a property (INCOMING_REQUEST) during a previous mediation. And hence using the first enrich mediator I am replacing the body of the current payload using that property.
So the second mediator is the one actually does the job.
It will take the OMElement given under source which is
and will insert as a child element of /BookingRequest/Booking xpath location in the INCOMING_REQUEST xml.
After enrich mediator
In this example I have modified the payload by adding only one xml element. Even if you need to add more elements also you can follow the same approach.
Many thanks to Rajith from WSO2 for the tip.