Temporary Fields

Fields prefixed with a single underscore _ are treated as temporary fields. They are valuable for intermediate calculations but are excluded from the final output.

How they work

When a field name starts with _, its value is still computed and available in the derived context for subsequent transforms, but it gets stripped from the final result.

Example

Input

{
  "price": 100,
  "quantity": 3
}

Output

{ "total": 330 }

Transforms

[
  { "_subtotal": "input.price * input.quantity" },
  { "_tax": "derived._subtotal * 0.1" },
  { "total": "derived._subtotal + derived._tax" }
]

The _subtotal (300) and _tax (30) fields are computed and available via derived during execution, but they do not appear in the final output — only total (330) is returned.

Use cases

• Multi-step calculations — Break complex logic into intermediate steps
• Conditional logic — Compute conditions without exposing them
• Derived data reuse — Avoid repeating the same sub-expression

Note

Temporary fields are only stripped at the top level and within transformed objects. If a temporary field's value is used in a sub-transformation's derived state, it must be manually referenced if needed.