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Single-value selector

Context

Section titled “Context”

In DataWeave, selectors are the main way to navigate a payload and pull data out of it. The most basic one is the single-value selector (.), which reads a property of an object by name.

Syntax

Section titled “Syntax”
payload.propertyName

It works like reading a key from a JSON object. If the payload is:

{
  "nombre": "Matías",
  "edad": 28,
  "ciudad": "Buenos Aires"
}

then payload.nombre returns "Matías".

Exercise

Section titled “Exercise”

Given the following input payload:

{
  "producto": {
    "id": "PROD-001",
    "nombre": "API Gateway",
    "precio": 150.00,
    "moneda": "USD",
    "activo": true
  }
}

Write a DataWeave transformation that produces this output:

{
  "nombreProducto": "API Gateway",
  "precioFinal": 150.00
}

Hints

Section titled “Hints”
  • Use the single-value selector (.) to reach the properties of the producto object.
  • Selectors can be chained: payload.producto.nombre.
🔒🔓Show solution

The DataWeave transformation would be:

%dw 2.0
output application/json
---
nombreProducto: payload.producto.nombre,
precioFinal: payload.producto.precio

Explanation:

  1. payload.producto reaches the nested producto object.
  2. .nombre and .precio are single-value selectors that read each property.
  3. A new object is built with the keys nombreProducto and precioFinal.

Check yourself

Section titled “Check yourself”

Answer these questions to confirm what you learned:

1. Which operator is the single-value selector in DataWeave?

2. Given a payload with a nested object, what does payload.a.b return if b is 42?

3. What happens if you use a single-value selector on a key that doesn't exist?

Result