MuleSoft DataWeave Transformations: Complete Guide with Examples

%dw 2.0
output application/json
 
// Basic transformation structure
{
    // Header section defines output format
    // Body section contains transformation logic
}

%dw 2.0
output application/json
 
var inputData = {
    "stringNum": "123",
    "dateString": "2025-01-15",
    "boolString": "true",
    "nullValue": null
}
 
---
{
    // Type coercion examples
    asNumber: inputData.stringNum as Number,
    asDate: inputData.dateString as Date {format: "yyyy-MM-dd"},
    asBoolean: inputData.boolString as Boolean,
 
    // Default values for null handling
    withDefault: inputData.nullValue default "N/A",
 
    // Conditional coercion
    safeNumber: if (inputData.stringNum is String)
                    inputData.stringNum as Number
                else
                    0
}

%dw 2.0
output application/xml
ns soap http://schemas.xmlsoap.org/soap/envelope/
ns ord http://example.com/orders
 
var orderJson = {
    "orderId": "ORD-12345",
    "customer": {
        "id": "CUST-001",
        "name": "Acme Corp",
        "email": "orders@acme.com"
    },
    "items": [
        {"sku": "PROD-A", "quantity": 10, "price": 25.99},
        {"sku": "PROD-B", "quantity": 5, "price": 49.99}
    ],
    "total": 509.85
}
---
{
    soap#Envelope: {
        soap#Header: {},
        soap#Body: {
            ord#CreateOrder: {
                ord#OrderHeader: {
                    ord#OrderId: orderJson.orderId,
                    ord#OrderDate: now() as String {format: "yyyy-MM-dd'T'HH:mm:ss"},
                    ord#Customer: {
                        ord#CustomerId: orderJson.customer.id,
                        ord#CustomerName: orderJson.customer.name,
                        ord#Email: orderJson.customer.email
                    }
                },
                ord#OrderLines: {
                    (orderJson.items map (item, index) -> {
                        ord#OrderLine: {
                            ord#LineNumber: index + 1,
                            ord#SKU: item.sku,
                            ord#Quantity: item.quantity,
                            ord#UnitPrice: item.price,
                            ord#LineTotal: item.quantity * item.price
                        }
                    })
                },
                ord#OrderTotal: orderJson.total
            }
        }
    }
}

%dw 2.0
output application/json
 
var xmlInput = read('<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
    <soap:Body>
        <GetCustomerResponse xmlns="http://example.com/customer">
            <Customer id="CUST-001" status="active">
                <Name>Acme Corporation</Name>
                <Addresses>
                    <Address type="billing" primary="true">
                        <Street>123 Main St</Street>
                        <City>New York</City>
                        <Country>USA</Country>
                    </Address>
                    <Address type="shipping">
                        <Street>456 Warehouse Blvd</Street>
                        <City>Newark</City>
                        <Country>USA</Country>
                    </Address>
                </Addresses>
                <Contacts>
                    <Contact role="primary">John Doe</Contact>
                    <Contact role="billing">Jane Smith</Contact>
                </Contacts>
            </Customer>
        </GetCustomerResponse>
    </soap:Body>
</soap:Envelope>', "application/xml")
 
---
{
    customer: {
        // Access attributes with @
        id: xmlInput.Envelope.Body.GetCustomerResponse.Customer.@id,
        status: xmlInput.Envelope.Body.GetCustomerResponse.Customer.@status,
        name: xmlInput.Envelope.Body.GetCustomerResponse.Customer.Name,
 
        // Transform addresses array
        addresses: xmlInput.Envelope.Body.GetCustomerResponse.Customer.Addresses.*Address map (addr) -> {
            addressType: addr.@type,
            isPrimary: addr.@primary default "false" == "true",
            street: addr.Street,
            city: addr.City,
            country: addr.Country
        },
 
        // Transform contacts with role mapping
        contacts: xmlInput.Envelope.Body.GetCustomerResponse.Customer.Contacts.*Contact map (contact) -> {
            role: contact.@role,
            name: contact
        }
    }
}

%dw 2.0
output application/json
 
var csvData = "employee_id|first_name|last_name|department|salary|hire_date
E001|John|Doe|Engineering|85000|2020-03-15
E002|Jane|Smith|Marketing|72000|2019-08-22
E003|Bob|Johnson|Engineering|92000|2018-01-10
E004|Alice|Williams|Sales|78000|2021-05-01"
 
var parsedCsv = read(csvData, "application/csv", {
    separator: "|",
    header: true
})
---
{
    totalEmployees: sizeOf(parsedCsv),
 
    // Group by department
    byDepartment: parsedCsv groupBy $.department mapObject ((employees, dept) -> {
        (dept): {
            count: sizeOf(employees),
            totalSalary: sum(employees.salary map ($ as Number)),
            avgSalary: avg(employees.salary map ($ as Number)),
            employees: employees map {
                id: $.employee_id,
                name: $.first_name ++ " " ++ $.last_name,
                salary: $.salary as Number
            }
        }
    }),
 
    // Find highest paid
    highestPaid: (parsedCsv orderBy -(($.salary) as Number))[0] then {
        name: $.first_name ++ " " ++ $.last_name,
        salary: $.salary as Number,
        department: $.department
    }
}

%dw 2.0
output application/csv separator=",", header=true, quoteValues=true
 
var jsonOrders = [
    {orderId: "O001", customer: "Acme", product: "Widget A", qty: 10, price: 25.99},
    {orderId: "O002", customer: "Beta Inc", product: "Widget B", qty: 5, price: 49.99},
    {orderId: "O003", customer: "Acme", product: "Widget C", qty: 20, price: 15.50}
]
---
jsonOrders map {
    "Order ID": $.orderId,
    "Customer Name": $.customer,
    "Product": $.product,
    "Quantity": $.qty,
    "Unit Price": $.price,
    "Line Total": $.qty * $.price,
    "Order Date": now() as String {format: "yyyy-MM-dd"}
}

%dw 2.0
output application/json
 
var salesData = [
    {region: "North", product: "A", q1: 100, q2: 150, q3: 120, q4: 180},
    {region: "North", product: "B", q1: 80, q2: 90, q3: 110, q4: 95},
    {region: "South", product: "A", q1: 200, q2: 180, q3: 220, q4: 250},
    {region: "South", product: "B", q1: 150, q2: 160, q3: 140, q4: 170},
    {region: "East", product: "A", q1: 90, q2: 100, q3: 95, q4: 110},
    {region: "West", product: "A", q1: 120, q2: 130, q3: 125, q4: 140}
]
 
// Helper function for annual total
fun annualTotal(record) = record.q1 + record.q2 + record.q3 + record.q4
---
{
    // Flatten quarterly data to rows
    flattenedData: salesData flatMap (record) -> [
        {region: record.region, product: record.product, quarter: "Q1", sales: record.q1},
        {region: record.region, product: record.product, quarter: "Q2", sales: record.q2},
        {region: record.region, product: record.product, quarter: "Q3", sales: record.q3},
        {region: record.region, product: record.product, quarter: "Q4", sales: record.q4}
    ],
 
    // Pivot: Region totals by quarter
    regionQuarterPivot: salesData groupBy $.region mapObject ((records, region) -> {
        (region): {
            Q1: sum(records.q1),
            Q2: sum(records.q2),
            Q3: sum(records.q3),
            Q4: sum(records.q4),
            Annual: sum(records map annualTotal($))
        }
    }),
 
    // Product performance ranking
    productRanking: (salesData groupBy $.product mapObject ((records, product) -> {
        (product): sum(records map annualTotal($))
    }) pluck ((value, key) -> {product: key, totalSales: value}))
        orderBy -$.totalSales,
 
    // Find best quarter per region
    bestQuarterByRegion: salesData groupBy $.region mapObject ((records, region) -> {
        (region): do {
            var totals = {
                Q1: sum(records.q1),
                Q2: sum(records.q2),
                Q3: sum(records.q3),
                Q4: sum(records.q4)
            }
            var maxVal = max(totals pluck $)
            ---
            (totals filterObject ((v, k) -> v == maxVal) pluck $$)[0]
        }
    }),
 
    // Distinct regions and products
    distinctRegions: salesData.region distinctBy $,
    distinctProducts: salesData.product distinctBy $,
 
    // Cross join for all combinations
    allCombinations: (salesData.region distinctBy $) flatMap ((region) ->
        (salesData.product distinctBy $) map ((product) -> {
            region: region,
            product: product
        })
    )
}

%dw 2.0
output application/json
 
var dynamicData = {
    "field_001": "value1",
    "field_002": "value2",
    "custom_abc": "valueA",
    "custom_xyz": "valueB",
    "metadata_created": "2025-01-15",
    "metadata_updated": "2025-01-20"
}
 
var keyMapping = {
    "field_001": "primaryField",
    "field_002": "secondaryField"
}
---
{
    // Rename keys dynamically
    renamedFields: dynamicData mapObject ((value, key) -> {
        ((keyMapping[key as String] default key)): value
    }),
 
    // Group by key prefix
    groupedByPrefix: dynamicData
        pluck ((value, key) -> {key: key, value: value})
        groupBy ((item) -> (item.key as String) splitBy "_")[0]
        mapObject ((items, prefix) -> {
            (prefix): items reduce ((item, acc = {}) -> acc ++ {
                (((item.key as String) splitBy "_")[1 to -1] joinBy "_"): item.value
            })
        }),
 
    // Filter keys by pattern
    customFieldsOnly: dynamicData filterObject ((v, k) ->
        (k as String) startsWith "custom_"
    ),
 
    // Dynamic key construction
    constructedObject: ["alpha", "beta", "gamma"] reduce ((item, acc = {}) ->
        acc ++ {("dynamic_" ++ item): upper(item)}
    )
}

%dw 2.0
output application/json
 
var inputPayload = {
    "orders": [
        {"id": "O1", "amount": "100.50", "currency": "USD", "date": "2025-01-15"},
        {"id": "O2", "amount": "invalid", "currency": "EUR", "date": "2025-01-16"},
        {"id": "O3", "amount": "200.00", "currency": null, "date": "bad-date"},
        {"id": null, "amount": "150.00", "currency": "GBP", "date": "2025-01-17"}
    ]
}
 
// Validation function
fun validateOrder(order) = {
    isValid: (order.id != null) and
             (order.amount is String and (order.amount matches /^\d+(\.\d{2})?$/)) and
             (order.currency != null) and
             (order.date is String and (order.date matches /^\d{4}-\d{2}-\d{2}$/)),
    errors: (
        (if (order.id == null) ["Missing order ID"] else []) ++
        (if (!(order.amount is String and (order.amount matches /^\d+(\.\d{2})?$/))) ["Invalid amount format"] else []) ++
        (if (order.currency == null) ["Missing currency"] else []) ++
        (if (!(order.date is String and (order.date matches /^\d{4}-\d{2}-\d{2}$/))) ["Invalid date format"] else [])
    )
}
 
// Safe type conversion
fun safeToNumber(val) =
    if (val is String and (val matches /^-?\d+(\.\d+)?$/))
        val as Number
    else
        null
 
fun safeToDate(val, format) =
    try (() -> val as Date {format: format})
    orElse null
---
{
    // Validate all orders
    validationResults: inputPayload.orders map ((order, index) -> {
        orderIndex: index,
        order: order,
        validation: validateOrder(order)
    }),
 
    // Separate valid and invalid
    validOrders: inputPayload.orders filter ((order) -> validateOrder(order).isValid),
 
    invalidOrders: inputPayload.orders
        map ((order, index) -> {order: order, index: index, validation: validateOrder(order)})
        filter ((item) -> !item.validation.isValid)
        map {
            orderIndex: $.index,
            originalData: $.order,
            errors: $.validation.errors
        },
 
    // Transform with safe conversions
    processedOrders: inputPayload.orders map ((order) -> {
        id: order.id default "UNKNOWN",
        amount: safeToNumber(order.amount) default 0,
        currency: order.currency default "USD",
        date: safeToDate(order.date, "yyyy-MM-dd"),
        processed: true
    }),
 
    // Summary
    summary: {
        total: sizeOf(inputPayload.orders),
        valid: sizeOf(inputPayload.orders filter ((o) -> validateOrder(o).isValid)),
        invalid: sizeOf(inputPayload.orders filter ((o) -> !validateOrder(o).isValid))
    }
}

// File: src/main/resources/dw/CommonFunctions.dwl
%dw 2.0
 
// String utilities
fun capitalize(str: String): String =
    upper(str[0]) ++ lower(str[1 to -1])
 
fun toTitleCase(str: String): String =
    str splitBy " " map capitalize($) joinBy " "
 
fun truncate(str: String, maxLen: Number): String =
    if (sizeOf(str) > maxLen)
        str[0 to maxLen - 4] ++ "..."
    else
        str
 
// Date utilities
fun formatDateISO(date: Date): String =
    date as String {format: "yyyy-MM-dd'T'HH:mm:ss'Z'"}
 
fun daysBetween(date1: Date, date2: Date): Number =
    (date2 - date1) as Number {unit: "days"}
 
fun isBusinessDay(date: Date): Boolean = do {
    var dayOfWeek = date as String {format: "E"}
    ---
    !(dayOfWeek == "Sat" or dayOfWeek == "Sun")
}
 
// Currency formatting
fun formatCurrency(amount: Number, currency: String): String = do {
    var symbols = {
        "USD": "\$",
        "EUR": "€",
        "GBP": "£"
    }
    ---
    (symbols[currency] default currency ++ " ") ++
    (amount as String {format: "#,##0.00"})
}
 
// UUID generation (simplified)
fun generateId(prefix: String): String =
    prefix ++ "-" ++ uuid() splitBy "-" joinBy ""
 
// Null-safe navigation
fun safeGet(obj: Object, path: String): Any =
    path splitBy "." reduce ((key, acc = obj) ->
        if (acc is Object) acc[key] else null
    )

%dw 2.0
output application/json
 
// Import custom module
import * from dw::CommonFunctions
 
var customerData = {
    name: "john doe",
    email: "JOHN.DOE@EXAMPLE.COM",
    description: "This is a very long description that should be truncated for display purposes in the UI",
    orderDate: "2025-01-15" as Date,
    orderTotal: 1234.56
}
---
{
    displayName: toTitleCase(customerData.name),
    email: lower(customerData.email),
    shortDescription: truncate(customerData.description, 50),
    orderDateFormatted: formatDateISO(customerData.orderDate),
    daysSinceOrder: daysBetween(customerData.orderDate, now()),
    totalFormatted: formatCurrency(customerData.orderTotal, "USD"),
    transactionId: generateId("TXN")
}

%dw 2.0
output application/json
 
// Use streaming for large files
// output application/json streaming=true
 
var largeDataset = (1 to 10000) as Array map {
    id: $,
    value: random() * 1000,
    category: ["A", "B", "C", "D"][mod($, 4)]
}
 
---
{
    // GOOD: Use reduce instead of multiple iterations
    optimizedAggregation: largeDataset reduce ((item, acc = {
        count: 0,
        sum: 0,
        categories: {}
    }) -> {
        count: acc.count + 1,
        sum: acc.sum + item.value,
        categories: acc.categories ++ {
            (item.category): (acc.categories[item.category] default 0) + 1
        }
    }),
 
    // GOOD: Filter early, transform later
    filteredFirst: largeDataset
        filter ($.value > 500)  // Reduce dataset size first
        map {                    // Then transform
            id: $.id,
            roundedValue: round($.value)
        },
 
    // GOOD: Use distinctBy with specific field
    uniqueCategories: largeDataset.category distinctBy $,
 
    // Limit output for previews
    preview: largeDataset[0 to 9]
}
 
/*
Performance Tips:
1. Use streaming for files > 10MB
2. Filter before mapping
3. Avoid nested loops - use groupBy and reduce
4. Use lazy evaluation with defer
5. Minimize type coercions in loops
*/