Introduction

HFF keeps query syntax and common compilation separate from backend building. Compile checks language semantics and selected capabilities; a backend then checks whether it can implement the compiled operations. Unsupported behavior must fail explicitly rather than being silently omitted.

• Local backend: build reusable filters, match validated values, configure local limits, and register local extension evaluators.
• PostgreSQL backend: build parameterized predicates, inspect backend guarantees, and register PostgreSQL method translators. Start with the PostgreSQL binding tutorial to connect a logical HFF record to relational rows. PostgreSQL-specific guides cover JSON/JSONB and native composite bindings, flattened structs, and correlated relations.

These builders do not own database execution. The application owns connections, transactions, and database timeouts. Consult the backend support matrices before relying on a particular operation.