How to combine 2 json payloads in wso2?

Question

I am making use of XSLT mediator to form the following JSON payload:

{
    "products": [
        {
          
            "product_id": 1,
            "product_name" : "abc"
           
        },
        {
            
            "product_id": 2,
           "product_name" : "xyz"
            
        }
    ]
}

Based on the response I get from the api using the above payload, I need to create another json payload(below) and append it to make another api call.

{
"amount": {
    "total_amount": 0.46,
    "total_tax": 0
  }
 }

I want the final payload to look like

 {
    "products": [
        {
          
            "product_id": 1,
            "product_name" : "abc"
           
        },
        {
            
            "product_id": 2,
           "product_name" : "xyz"
            
        }
    ],
    
    "amount": {
    "total_amount": 0.46,
    "total_tax": 0
  }
}

How can I achieve this on WSO2 Integration studio?

Answer 1

I think XSLT is an overkill for this and I don't think Datamapper is a viable option here, given we are dealing with multiple inputs. You can simply use the Enrich Mediator for this. Here is an example for your payloads. I tried to provide an example as close to your requirement, I have hardcoded the payloads, and the Payload Factory depicts your backend call response and the original PL.

<?xml version="1.0" encoding="UTF-8"?>
<api context="/json" name="TestAPI" xmlns="http://ws.apache.org/ns/synapse">
    <resource methods="GET">
        <inSequence>
            <payloadFactory description="Build JSON" media-type="json">
                <format>
                    {
                        "products": [
                            {
                                "product_id": 1,
                                "product_name" : "abc"   
                            },
                            {  
                               "product_id": 2,
                               "product_name" : "xyz"                               
                            }
                        ]
                    }
                    </format>
                <args/>
            </payloadFactory>
            <enrich description="First save the Original PL to a property" >
                <source clone="true" type="body"/>
                <target property="ORIGINAL_PL" type="property"/>
            </enrich>
            <payloadFactory description="Build JSON second PL" media-type="json">
                <format>
                    {
                        "amount": {
                            "total_amount": 0.46,
                            "total_tax": 0
                          }
                    }
                    </format>
                <args/>
            </payloadFactory>
            <enrich description="Save the PL from the second request to another property">
                <source clone="true" type="body"/>
                <target property="SECOND_PL" type="property"/>
            </enrich>
            <enrich description="Restore original payload">
                <source clone="false" property="ORIGINAL_PL" type="property"/>
                <target type="body"/>
            </enrich>
            <enrich description="Now add the second PL as a Child to the original" >
                <source clone="true" property="SECOND_PL" type="property"/>
                <target action="child" xpath="json-eval($)"/>
            </enrich>
            <log level="full"/>
            <respond/>
        </inSequence>
        <outSequence/>
        <faultSequence/>
    </resource>
</api>

This is the result of the above.

{
  "products": [
    {
      "product_id": 1,
      "product_name": "abc"
    },
    {
      "product_id": 2,
      "product_name": "xyz"
    }
  ],
  "amount": {
    "total_amount": 0.46,
    "total_tax": 0
  }
}