Message Element Setter mediation primitive

Introduction

You can use the Message Element Setter mediation primitive to provide a simple mechanism for setting message content, it does not change the type of the message. You can change, add or delete message elements by setting the mediation primitive properties.

If you want multiple message changes you can set multiple targets. Multiple target elements are set sequentially, in the order in which they are specified; this means that elements can build on each other.

You can set target elements to a constant value, or to a value copied from somewhere in the input service message object (SMO). If a target element you specify does not exist, it is created in the SMO. You can also delete message elements, if they are optional or repeating elements.

Target elements are specified as XPath expressions using the Target property. If you set a target element to a constant value, the target XPath must resolve to a single leaf in an SMO node. If you set a target element from a source element, both the source and target XPaths must resolve to a single element (a single leaf or subtree). You can use the Value property to specify either a constant value or a source XPath expression.

The Message Element Setter mediation primitive has one input terminal (in), one output terminal (out) and a fail terminal (fail). The in terminal is wired to accept a message and the other terminals are wired to propagate a message. If the mediation is successful, the out terminal propagates the modified message. If an exception occurs during the transformation, the fail terminal propagates the original message, together with any exception information contained in the failInfo element.

Usage

Because the operations you define occur sequentially, a later operation can depend on an earlier operation. For example, you could define a copy operation to copy a new element into the SMO, and a later operation to set a value in the newly copied element.

It is often useful to combine the Message Element Setter mediation primitive with other mediation primitives. For example, you can use the Message Element Setter mediation primitive if you need to manipulate data, before or after the Database Lookup mediation primitive is invoked.

You can also use the Message Element Setter mediation primitive to change messages after filtering them, using the Message Filter mediation primitive. You might want to update or delete certain message elements after filtering.