Introduction
Here is a problem I am facing. An incoming JSON payload misses a piece of information, the transaction type. This piece of information can be deducted from the existing information. Actually, the really application is more more complicated. In this Mule Dev Trick, I am going to demonstrate how to add new information to the payload.
This small piece of code involves several key concept of Dataweave:
- map
- mapObject
- Condition statement
- Lamda sytax
Input Payload
[ { "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": "" } ]
The Desired Output
[ { "worker_id": "AMAGWK00002673", "position_id": "35119973", "requisition_id": "R-32353", "applicant_id": "199505", "staff_id": "199504", "type": "re-hire" }, { "worker_id": "AMAGWK00002674", "position_id": "35119943", "requisition_id": "R-32353", "applicant_id": "199505", "staff_id": "199506", "type": "re-hire" }, { "worker_id": "AMAGWK00002675", "position_id": "35119975", "requisition_id": "R-32354", "applicant_id": "199507", "staff_id": "", "type": "new-hire" } ]As you can see that the "type" attribute is introduced based on whether the staff_id is empty or not. If the staff_id attribute is not empty, I set the value of this attribute to "re-hire", otherwise, it will be "new-hire".
Solution
%dw 1.0 %output application/json --- payload map ((worker) ->{ (worker mapObject (value, key) -> { "$key" : value }), type : "new-hire" when worker.staff_id == null or worker.staff_id == '' otherwise 're-hire' })Note: the $key is used here. There is another syntax is (key). Thus, the above code can be as the following:
%dw 1.0 %output application/json --- payload map ((worker) ->{ (worker mapObject (value, key) -> { (key) : value }), type : "new-hire" when worker.staff_id == null or worker.staff_id == '' otherwise 're-hire' })
Key Learning Points
The above script seems pretty simple. It has used many key concepts of the DataWeave component. The key of the map function is to iterate a List or Array and produce a new array. And the main usage of mapObject is to iterate the attributes of an object. Both functions use Lamda expression which takes two value, $$, $. By default, $ represent the value of the current object the iterator is point to, and $$ is the index or key of the object.
Another worth noting point is that map can take single argument as well.
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