mulesoft-dataweave

name: mulesoft-dataweave description: "DataWeave 2.0 transformation expert for MuleSoft. Covers syntax (types, variables, functions), common patterns (object map, filter, reduce, groupBy), format handling (JSON/XML/CSV/Java/Form), field mapping between systems (NS ↔ SF ↔ DB), watermark logic, date/time manipulation, and error-safe defaults. Use when writing any ee:transform, debugging a DataWeave script, or mapping fields between source and target systems."

Skill: DataWeave 2.0 Transformations

Purpose

Write correct, readable, error-safe DataWeave 2.0 transforms for MuleSoft flows. Covers the 80% of patterns used in real integrations: field mapping, filtering, format conversion, date handling, defaults, null-safety.

When to Use

• Mapping fields between source and target systems (NS → SF, SF → DB, etc.)
• Converting between JSON, XML, CSV, Java, and Form formats
• Filtering, grouping, or reshaping collections
• Computing watermarks or derived fields
• Handling null-safety and defaults

When NOT to Use

• Flow structure, triggers, or routing — use /mulesoft-flow
• Connector config — use /mulesoft-connector
• Deploying — use /mulesoft-platform

Non-Negotiable Rules

1. Always declare output at the top — e.g. output application/json
2. Always handle nulls — use default operator or ? safe navigation
3. Never hardcode magic values — declare as var at top
4. Never silent-coerce types — explicit as String, as Number, as Date where ambiguous
5. Always separate variables (var) and functions (fun) at the top, mapping logic at the bottom
6. Always comment non-obvious transforms — future you will forget what "1 day before settlement" logic meant

Standard DataWeave Structure

%dw 2.0
output application/json

// Variables
var onStopTriggers = ["CUSTOMER-ACCOUNT ON STOP", "CUSTOMER-SUSPENDED"]

// Functions
fun isOnStop(status) = status in onStopTriggers

// Transformation (after ---)
---
payload map (customer) -> {
  id: customer.internalId,
  onStop: isOnStop(customer.entityStatus.name) default false
}

Modes

Core Operators

Output Formats

output application/json              // JSON
output application/xml               // XML
output application/csv               // CSV
output application/java              // Java objects (for DB inserts)
output application/x-www-form-urlencoded  // Form data
output application/dw                // DataWeave (debugging)

Templates

Proactive Triggers

• DataWeave script without output declaration → flag as broken
• Field access without default on optional fields → flag as null-risk
• Magic strings hardcoded in mapping → flag, suggest extract to var
• Date handling without explicit timezone → flag as timezone-ambiguous
• Collection operations on potentially-null payload → flag for null-check

Anti-Patterns (do NOT do these)

• Writing transforms without output — won't compile
• Accessing nested fields without null-safety (payload.address.city crashes if address is null — use payload.address?.city default "")
• Hardcoding trigger values in the mapping instead of a named var
• Using string concat for building SQL or URLs — use placeholders
• Swallowing DataWeave errors with try blocks around entire script — surface them

Related Skills

• Use /mulesoft-flow for the flow that wraps the transform
• Use /mulesoft-connector for understanding source/target data shapes
• Use /mulesoft-bdr for BDR-specific field name mappings