Backend-specific Features

Some database features are not portable across backends. Rango exposes them via backend-specific traits rather than hiding or faking portability.

Philosophy

If a feature doesn't exist on a backend, it's simply not available — no silent fallbacks, no emulation that changes semantics.

#![allow(unused)]
fn main() {
// This compiles and runs only with the postgres feature
use rango::PgQueryExt;

Post::filter(&pool)
    .json_contains("metadata", json!({"status": "published"}))
    .all()
    .await?
}

If you migrate from Postgres to SQLite, the compiler tells you exactly where backend-specific code is used.

PgQueryExt (Postgres)

Method	SQL	Description
`.fts(col, query)`	`to_tsvector(...) @@ plainto_tsquery(...)`	Full-text search
`.fts_lang(col, query, lang)`	Same with custom language	FTS with language config
`.json_contains(col, val)`	`col @> val::jsonb`	JSONB containment
`.json_has_key(col, key)`	`col ? key`	JSONB key existence
`.json_field_eq(col, key, val)`	`col->>'key' = val`	JSONB field equality
`.array_contains(col, vals)`	`col @> ARRAY[...]`	Array containment

SqliteQueryExt (SQLite)

Method	SQL	Description
`.json_extract_eq(col, path, val)`	`json_extract(col, path) = ?`	JSON field equality
`.json_extract_like(col, path, pat)`	`json_extract(col, path) LIKE ?`	JSON field LIKE
`.json_extract_exists(col, path)`	`json_extract(col, path) IS NOT NULL`	JSON key existence
`.fts5(table, query)`	`rowid IN (SELECT rowid FROM fts WHERE fts MATCH ?)`	FTS5 search

Adding to the prelude

Each trait is available via use rango::prelude::* when its backend is enabled, whichever backend supplies the prelude's ops (see "Several backends at once" in Installation).

Future extensions

Planned backend-specific features:

PgQueryExt: window functions, DISTINCT ON, advisory locks
SqliteQueryExt: json_each(), json_group_array()
MySqlQueryExt: MySQL / MariaDB JSON functions