Mule Dev Tricks: DataWeave Using Reduction

Introduction

In this post, I am going to demonstrate how to convert an array of JSON payload to a single JSON payload.

Input

[
  {
    "worker_id": "AMAGWK00002673",
    "position_id": "35119973",
    "requisition_id": "R-32353",
    "applicant_id": "199505",
    "staff_id": "199504"
  },
  {
    "worker_id": "AMAGWK00002674",
    "position_id": "35119943",
    "requisition_id": "R-32353",
    "applicant_id": "199505",
    "staff_id": "199506"
  },
  {
    "worker_id": "AMAGWK00002675",
    "position_id": "35119975",
    "requisition_id": "R-32354",
    "applicant_id": "199507",
    "staff_id": "199508"
  }
]

Desired Output

{
  "AMAGWK00002673": "199504",
  "AMAGWK00002674": "199506",
  "AMAGWK00002675": "199508"
}

Solution

The first step is to use dataweave to extrace the worker_id. This is very straight forward. The only trick about this piece of script is to use value as key in the transformed JSON result. This is achieved by using ($.key) : $.otherKey. here key = worker_id and the otherKey is staff_id.

payload map ((value, index) -> {
     (value.worker_id): value.staff_id 
}) 

The above dataweave script will produce the following result:

[
  {
    "AMAGWK00002673": "199504"
  },
  {
    "AMAGWK00002674": "199506"
  },
  {
    "AMAGWK00002675": "199508"
  }
]

In order to produce the final result, we need to use reduction reduce($$ + $).

payload map ((value, index) -> {
     (value.worker_id): value.staff_id 
}) reduce($$ ++ $)

Note: You have to use reduce ($$ ++$). The round bracket is important! The MuleSoft documentation missed that which causes many confusions.