Merge fields from multiple nested arrays in JSON input into new payload array using Dataweave - anypoint-studio

Question

I am using Anypoint Studio 7.3 and Mule 4.2.
Using the JSON input below, I would like to create new payloads to write to database tables including a payload which builds a list of customers from each record entry in the array to create a list entry looking like this:
[{
recordId,
customerId
}]
and the same for a list of transactions with each list entry looking like this:
[{
recordId
customerId
transactionId
}]
but when I try to transform the data the field values show either as null or as a list instead of a single field in the object like this:
{
"customers": [{
"record": "1234",
"customerId": [
"5435e1cd-146d-4aac-9164-4a2d80d5eccd"
]
}]
}
instead of this:
{
"customers": [{
"recordId": "1234",
"customerId": "5435e1cd-146d-4aac-9164-4a2d80d5eccd"
}]
}
JSON INPUT:
{
"records": [{
"recordId": "1234",
"customers": [{
"customerId": "1234",
"transactions": [{
"transactionId": "1234",
"prices": [{
"priceId": "1234",
"price": 1.00
}]
}]
}]
}]
}
Thanks for any help

Answer 1

In order to return the list of customers from each record
%dw 2.0
output application/java
---
payload.records flatMap
((record, index) ->
record.customers map ((customer, index) ->
{
recordId: record.recordId,
customerId: customer.customerId
}
)
)
And for returning list of transactions with each list entry
%dw 2.0
output application/json
---
payload.records flatMap
((record, index) ->
record.customers flatMap ((customer, index) ->
customer.transactions map ((transaction, index) ->
{
recordId: record.recordId,
customerId: customer.customerId,
transactionId: transaction.transactionId
}
)
)
)
The key part here is using flatMap for flattening nesting levels of arrays into one.