tomferon / morph

Small migrator for PostgreSQL in Haskell

What is it?

Morph is a simple tool to migrate databases on PostgreSQL. It supports rollbacking from other versions without requiring the migration files from the previous version. Hence, to migrate to a new version, you only need the migration files from this particular version.

Migration files

Each migration file should be prefixed with a numerical identifier. These identifiers determine the order in which the migrations are going to be ran. Thus, a good way to avoid conflict with other commiters is to prefix it with a timestamp formatted as YYYYMMDDHHMM.

Each migration has two SQL files: one ending with .up.sql and the other by .down.sql, respectively the request to migrate and the one to rollback. Failing to have a .down.sql file will result in an error when attempting to rollback but will not prevent the initial migration.

For example, you could have the following files:

migrations/201603291434_create_users.up.sql

CREATE TABLE users (
       id       serial  PRIMARY KEY,
       username varchar NOT NULL UNIQUE CHECK (username <> ''),
       password varchar NOT NULL CHECK (password <> '')
);

migrations/201603291434_create_users.down.sql

DROP TABLE users;

migrations/201604011203_add_email_to_user.up.sql

ALTER TABLE users ADD COLUMN email varchar;

migrations/201604011203_add_email_to_user.down.sql

ALTER TABLE users DROP COLUMN email;

Options

See morph --help for details about command-line options.