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Define a Custom Addition Function

This DataWeave example takes in a set of item prices and stock amounts and uses several functions to calculate subtotals, deduct discounts and add taxes. Before you begin, note that DataWeave version 2 (%dw 2.0) is for Mule 4 apps. For a Mule 3 app, refer to DataWeave version 1 (%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.

It makes use of the following:

  • map function to go through all the items in the input.

  • basic math operations like *, + and -.

  • String concatenation with ++.

  • as to force string values into numbers.

  • Fixed values in the header to set tax and discount amounts.

  • A custom function in the header, to define once and use multiple times in the code.

  • reduce function to aggregate the various items into a total.

DataWeave Script:
%dw 2.0
output application/json
var tax = 0.085
var discount = 0.05
fun getSubtotal (items) = items reduce ((item, accumulator = 0) ->
        accumulator + (item.unit_price * item.quantity * (1 - discount)))
---
invoice: {
    header: payload.invoice.header,
    items: { (payload.invoice.items map {
        item : {
            description: $.description,
            quantity: $.quantity,
            unit_price: $.unit_price,
            discount: (discount * 100) as Number ++ "%",
            subtotal: $.unit_price * $.quantity * (1 - discount)
        }
    }) },
    totals:
    {
        subtotal: getSubtotal(payload.invoice.items ),
        tax: (tax * 100) as Number ++ "%",
        total: getSubtotal(payload.invoice.items ) * (1 + tax)
    }
}
Input JSON Payload:
{
  "invoice": {
    "header": {
      "customer_name": "ACME, Inc.",
      "customer_state": "CA"
    },
    "items": [
      {
        "description": "Product 1",
        "quantity": "2",
        "unit_price": "10"
      },
      {
        "description": "Product 2",
        "quantity": "1",
        "unit_price": "30"
      }
    ]
  }
}
Output
{
  "invoice": {
    "header": {
      "customer_name": "ACME, Inc.",
      "customer_state": "CA"
    },
    "items": {
      "item": {
        "description": "Product 1",
        "quantity": "2",
        "unit_price": "10",
        "discount": "5%",
        "subtotal": 19.00
      },
      "item": {
        "description": "Product 2",
        "quantity": "1",
        "unit_price": "30",
        "discount": "5%",
        "subtotal": 28.50
      }
    },
    "totals": {
      "subtotal": 47.50,
      "tax": "8.500%",
      "total": 51.53750
    }
  }
}

See Also