Dynamically add new element to json payload in WSO2 EI by using enrich mediator - json

Question

I need to enrich existing json payload with new elements which is dynamically passed to existing payload instead of static value. Can anyone please help me?
Existing payload:
{
"Type":"CAR",
"Identifier":"2db23c39-9d3f-4e61-b3c5-e8725a2f1b90",
"ListingType":"New",
"SaleStatus":"For Sale"
}
Expected :
{
"Type":"CAR",
"Identifier":"2db23c39-9d3f-4e61-b3c5-e8725a2f1b90",
"ListingType":"New",
"SaleStatus":"For Sale",
"messageId":"urn:uuid:ccdafb72-c4"
}
Here messageId is ESB generated MessageID automatically.
<!-- ************API Request set to incomingRequest property************ -->
<property description="incomingRequest" expression="json-eval($.)" name="incomingRequest"
scope="default" type="STRING"/>
<payloadFactory media-type="json">
<format>$1</format>
<args>
<arg evaluator="xml" expression="get-property('incomingRequest')"/>
</args>
</payloadFactory>
<enrich description="">
<source type="inline" clone="true">
<messageId xmlns="">evaluate(get-property('operation','messageId'))
</messageId>
</source>
<target action="child" xpath="//jsonObject" />
</enrich>
<enrich>
<source clone="true" xpath="//jsonObject" />
<target type="body" />
</enrich>
<log level="full"/>
**Getting Wrong output**
{
"Type":"CAR",
"Identifier":"2db23c39-9d3f-4e61-b3c5-e8725a2f1b90",
"ListingType":"New",
"SaleStatus":"For Sale",
"messageId": "evaluate(get-property('operation','messageId'))"
}
Note:
I have followed this

Answer 1

Inline content on the enrich mediator is not evaluated. (considered as string)
So, we can use the property mediator to evaluate the expression.
<property name="prop1" expression="get-property('operation','messageId')"/>
Then we can use the above property in enrich mediator.
<enrich description="">
<source type="property" property="prop1"></source>
<target action="child" xpath="//jsonObject" />
</enrich>
BTW, In latest product versions, the Enrich mediator has the native JSON support.
More details in Here

Answer 2

I had similar scenario where i wanted to append some elements to a received json response:
First i got the response received into a property:
property expression="json-eval($)" name="RESPONSE" scope="default"
type="STRING"
Then i created a payload and added the new properties:
<payloadFactory media-type="json">
<format>
{"details": $1,
"timestamp":"$2",
"value":"$3"}
</format>
<args>
<arg evaluator="xml"
expression="get-property('RESPONSE')" />
<arg evaluator="xml"
expression="get-property('REQUEST_TIMESTAMP')" />
<arg evaluator="xml"
expression="get-property('VALUE')" />
</args>
</payloadFactory>
Then I returned the response using loopback. Note that REQUEST_TIMESTAMP and VALUE are defined as properties.