[SOLVED] Mule 3 vs Mule 4 - is payload immutable?

Mule 3 vs Mule 4 - is payload immutable?

We are migrating a Mule 3 api to Mule 4 and am observing some behaviour which am not able to make sense of in Mule 3 .....

We have an incoming payload from an HTTP endpoint

{
   empId: 10,
   empAge: 23,
   empName: "Xyz",
   bonus: "N",
   performance: "Good",
   reward: "N" 
}

which we are storing in a variable:

<set-variable variableName="originalPayload" value="#[payload]" doc:name="Store original payload"/>

We then have a Groovy component that is performing some logic for bonus:

<scripting:script engine="Groovy"><![CDATA[
if (flowVars.originalPayload.empAge > 20) {
    flowVars.originalPayload.put("bonus", "Y")
}
return payload]]>
</scripting:script>
</scripting:component>

Here I can see that 'bonus' is now set to 'Y' in both the originalPayload ( expected ) and also in the payload ( not expected )

The above happens after the execution of Groovy component.

Further into the flow - we are using an expression component:

<expression-component doc:name="Set reward">
<![CDATA[if (payload.performance == "Good")  { payload.reward = "Y" }]]>
</expression-component>

after code executes the above expression as well reward is now reflecting as 'Y' in both payload ( expected ) and also iin flowVars.originalPayload ( Not expected )

In Mule 4 am replacing Groovy and expression with Dataweave transform component and the changes done for bonus reflect only in originalPayload ( expected ) but not in payload . Similarly reward in Mule 4 is now reflecting as 'Y' ONLY in payload ( expected ) and NOT in vars.originalPayload

so in short Mule 4 behaviour makes sense but not the Mule 3 behaviour .

Can someone please explain why we see this behaviour in Mule 3 ?

Solution

Same as Java -Mule is developed in Java- the variables and payload the payload and flow variables are object references, because they are Java objects. Thus when you are assigning the payload to a variable both will be reference to the same object instance. Your payload seems to be a Map. If you change the value of a key using either reference they are accessing the same object.

DataWeave -in both Mule versions- always generates a new output object, so the references will be different.