DSL Guide

The ETL Engine ships its own mapping language for the cases that Rabbit-in-a-Hat alone cannot express — joins, conditional chains, vocabulary lookups, multi-sized results, and so on. This guide covers the language in depth.

Pages

• Mapping Language Syntax — formal grammar and worked examples.
• Pipelines and Chaining — the => operator for explicit rule chains and named field bindings.
• Conditional Chaining — the || operator for fallbacks between rules.
• Multi-Sized Results — [] and [N] suffixes, LoopOver, and how multi-result rules fork execution paths.
• Arrays and New Mode — the ARRAY value type, new mode configuration, and array-aware rules.
• ForEach and Blocks — the | ForEach operator and block syntax.
• Virtual Fields — defining and using virtual fields on CDM tables.

Where rules live in Rabbit-in-a-Hat

The engine reads rules from four places in the Rabbit-in-a-Hat model:

1. Source-to-CDM table maps — rules placed on the arrow from a source table to a CDM table act as table-level rules.
2. CDM tables — rules placed on a CDM table itself, in the Comments field, with the prefix logic:.
3. Source-to-CDM field maps — rules on the arrow from a source field to a CDM field; default behaviour for field-to-field mappings.
4. CDM fields — rules placed on a CDM field, in the Comments field, with the prefix logic: (or field: to declare a virtual field).

The full list of rules per category is in the Rule Reference.