Extensions — ASL

Extensions

use extension '<name>'; enables a Postgres extension. It lowers to CREATE EXTENSION IF NOT EXISTS, emitted before tables and functions in a migration (and dropped last on the way down), so anything that depends on it — a function, a default, a column type — is created after it exists.

use extension 'unaccent';
use extension 'uuid-ossp';   # quoted, so hyphenated names work

CREATE EXTENSION IF NOT EXISTS "unaccent";
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

Extensions are tracked in the migration snapshot: declaring one adds a CREATE EXTENSION, removing the declaration adds a DROP EXTENSION to the next migration, and an unchanged declaration produces no diff.

Nothing is enabled automatically. In particular, gen_uuid() defaults compile to gen_random_uuid(), which requires pgcrypto — so declare it explicitly:

use extension 'pgcrypto';

A common pairing is an extension plus a function that uses it:

use extension 'unaccent';

@language plpgsql
@immutable
function slugify(value: text) -> text {
  return lower(public.unaccent(value));
};

Custom Extension Types

Extensions like PostGIS (postgis), pgvector (vector), and citext introduce custom PostgreSQL data types. You can declare scalars that map directly to these extension types using extends sql "<type>", and define client-side typing with as:

use extension 'postgis';
use extension 'vector';
use extension 'citext';

# 1. Structured record representation with deserialize and serialize receiver functions
scalar type Point extends sql "geography(Point, 4326)" as {
  latitude:   float32;
  longitude:  float32;
};

function (p Point) deserialize() Point {
  return Point{ latitude: ST_Y(p::geometry), longitude: ST_X(p::geometry) };
};

function (p Point) serialize() {
  return ST_SetSRID(ST_MakePoint(p.longitude, p.latitude), 4326);
};

# 2. Multi-dimensional array representation (codegen emits number[] / []float32)
scalar type Embedding extends sql "vector(1536)" as multi float32;

# 3. Primitive scalar alias (codegen emits string)
scalar type Citext extends sql "citext" as str;

# 4. Opaque custom SQL type (defaults to 'str' in host codegen)
scalar type Geometry extends sql "geometry";

type Venue {
  required id: uuid { constraint pk; };
  name:        Citext;
  location:    Point;
  feature_vec: Embedding;
  geom:        Geometry;
}

Benefits:

• Exact DDL: Generated migration SQL produces columns with the precise PostgreSQL type (e.g. geography(Point, 4326), vector(1536)).
• Client Typing: SDK generators produce typed interfaces/structs (Point as { latitude: number, longitude: number }, Embedding as number[]).
• AQL Dot-Access & Sub-shapes: Structured fields can be traversed directly in AQL expressions (.location.latitude) and projected with sub-shapes (select Venue { location: { latitude, longitude } }).
• Zero-Overhead SQL Inlining: Queries automatically inline PostGIS conversions (json_build_object on reads, ST_SetSRID on writes).

See Functions for the full function syntax and Aliases & Extended Types for more on custom scalar types.