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Rename JSON Keys

This DataWeave example renames some keys in a JSON object, while retaining the names of all others in the output. Before you begin, note that DataWeave 2.0 (%dw 2.0) is for Mule 4 apps. For a Mule 3 app, refer to DataWeave 1.0 (%dw 1.0) examples, within the Mule 3.9 documentation set. For other Mule versions, you can use the Mule Runtime version selector in the table of contents.

The example uses these functions:

  • mapObject to go through the key:value pairs in a JSON object.

  • if by itself to determine when to change the name of a key.

  • if with and to retain the name of all keys except the two with new names.

  • as to coerce the type of the keys into a String.

DataWeave Script:
%dw 2.0
output application/json
---
payload.flights map (flight) -> {
    (flight mapObject (value, key) -> {
        (emptySeats: value) if(key as String == 'availableSeats'),
        (airline: value) if(key as String == 'airlineName'),
        ((key):value) if(key as String !='availableSeats' and key as String != 'airlineName')
    })
}
Input JSON Payload:
{
  "flights":[
  {
  "availableSeats":45,
  "airlineName":"Ryan Air",
  "aircraftBrand":"Boeing",
  "aircraftType":"737",
  "departureDate":"12/14/2017",
  "origin":"BCN",
  "destination":"FCO"
  },
  {
  "availableSeats":15,
  "airlineName":"Ryan Air",
  "aircraftBrand":"Boeing",
  "aircraftType":"747",
  "departureDate":"08/03/2017",
  "origin":"FCO",
  "destination":"DFW"
  }]
}
Output JSON:
[
  {
    "emptySeats": 45,
    "airline": "Ryan Air",
    "aircraftBrand": "Boeing",
    "aircraftType": "737",
    "departureDate": "12/14/2017",
    "origin": "BCN",
    "destination": "FCO"
  },
  {
    "emptySeats": 15,
    "airline": "Ryan Air",
    "aircraftBrand": "Boeing",
    "aircraftType": "747",
    "departureDate": "08/03/2017",
    "origin": "FCO",
    "destination": "DFW"
  }
]

A more maintainable way to produce the same output uses DataWeave pattern matching.

The example uses the following functions and statements:

  • mapObject to go through the key:value pairs in a JSON object.

  • match on each key in the input.

  • case statements to change the name of matching keys in the input.

  • else statement to retain the name of keys that do not require a name change.

DataWeave Script:
%dw 2.0
output application/json
fun renameKey(key: Key) = key match {
    case "availableSeats" -> "emptySeats"
    case "airlineName" -> "airline"
    else -> (key)
}
---
payload.flights map (flight) ->
flight mapObject (value, key) -> {
    (renameKey(key)) : value
}
Input JSON Payload:
{
  "flights":[
  {
  "availableSeats":45,
  "airlineName":"Ryan Air",
  "aircraftBrand":"Boeing",
  "aircraftType":"737",
  "departureDate":"12/14/2017",
  "origin":"BCN",
  "destination":"FCO"
  },
  {
  "availableSeats":15,
  "airlineName":"Ryan Air",
  "aircraftBrand":"Boeing",
  "aircraftType":"747",
  "departureDate":"08/03/2017",
  "origin":"FCO",
  "destination":"DFW"
  }]
}
Output JSON:
[
  {
    "emptySeats": 45,
    "airline": "Ryan Air",
    "aircraftBrand": "Boeing",
    "aircraftType": "737",
    "departureDate": "12/14/2017",
    "origin": "BCN",
    "destination": "FCO"
  },
  {
    "emptySeats": 15,
    "airline": "Ryan Air",
    "aircraftBrand": "Boeing",
    "aircraftType": "747",
    "departureDate": "08/03/2017",
    "origin": "FCO",
    "destination": "DFW"
  }
]

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