Schema Language (ASL)

Axel Schema Language (ASL)

ASL is a declarative schema language for defining PostgreSQL types. You write .asl files; Axel compiles them into migration SQL that you apply with axel diff and axel up.

schema.asl

A schema can also be split across several files with a glob such as schema/*.asl.

How ASL is organized

An ASL file is a set of top-level declarations. The reference is split by feature:

• Schema — concrete and abstract types, inheritance (extends), indexes, and composite constraints.
• Data Types — built-in scalars, named scalar aliases, typed JSON, and enums.
• Fields — properties, defaults, rewrites, field constraints, links, and computed fields.
• Functions — top-level Postgres functions with AQL or raw-SQL bodies.
• Triggers — row/statement triggers attached to a type.
• Splitting a Schema — spread declarations across several .asl files.

Complete example

A schema that touches most features:

scalar type EmailStr extends str;

enum Role { Admin, Member, Guest }

abstract type Base {
  required id: uuid {
    default := gen_uuid();
    constraint pk;
  };
  required created_at: datetime { default := datetime_current(); };
  required updated_at: datetime {
    default := datetime_current();
    rewrite update := datetime_current();
  };
}

type User extends Base {
  required email: EmailStr {
    constraint exclusive;
  };
  name: str;
  required age: int32;
  active: bool { default := true };
  required role: Role;

  computed display_name := .name ?? .email;

  index on (.email);
}

type Post extends Base {
  required title: str;
  required content: str;
  required link author: User;
  multi link likes: User;
}

type Comment extends Base {
  required link post: Post;
  required link author: User;
  required content: str;
}