Migrating the Enricher to a Target Variable

The Message Enricher and its functionality in Mule 3 is replaced by the target parameter in Mule 4. The Enricher provided a way to execute a group of message processors and redirect their output to a variable without side effects to the current message. In Mule 4, all non-void operations (for example, <flow-ref>, <http:request>, <db:select>, and so on) include target and targetValue parameters, which allow redirecting each operation’s output into a variable (such as myVar). Other components in a Mule flow can then access that data through a DataWeave selector (for example, vars.myVar).

Example

Consider a message coming from an HTTP request, which we want to redirect to a third system, only that adding a state query param which is to be extracted using a secondary flow called stateLookup. Because you don’t want to lose the original payload or headers, you need to extract this value without affecting the original message. The Enricher calls out to the enrichment resource with the current message (containing the zip code), then enriches the current message with the result.

Mule 3 example

<flow name="orderProcessingFlow">
   <http:listener .../>
   <enricher target="#[variable:state]">
       <flow-ref name="stateLookup"/>
   </enricher>
  <http:request config-ref="config" path="state" method="POST">
    <http:request-builder>
        <http:query-param paramName="state" value="#[flowVars.state]" />
    </http:request-builder>
  </http:request>
</flow>

In Mule 4, you can simply use the target parameter in the <flow-ref> operation:

Mule 4 example

<flow name="orderProcessingFlow">
  <http:listener .../>
  <flow-ref name="stateLookup" target="state" />
  <http:request config-ref="config" path="state" method="POST">
    <http:query-params>
      #[{'state' : vars.state}]
    </http:query-params>
  </http:request>
</flow>

Migrate Multiple Enrichers

In Mule 4, you can set only one target variable per operation. If you have more than one enricher configured in your Mule 3 application, you can achieve the same behavior in Mule 4 by using the Set Variable component: