Micrate is a database migration tool written in Crystal.
It is inspired by goose. Some code was ported from there too, so check it out.
Micrate currently supports migrations for Postgres, Mysql and SQLite3, but it should be easy to add support for any other database engine with an existing crystal-db API driver.
To install the standalone binary tool check out the releases page, or use homebrew:
$ brew tap amberframework/micrate $ brew install micrate
micrate help for usage instructions. Micrate will connect to the database specified by the
DATABASE_URL environment variable.
To create a new migration use the
scaffold subcommand. For example,
micrate scaffold add_users_table will create a new SQL migration file with a name such as
db/migrations/20160524162446_add_users_table.sql that looks like this:
-- +micrate Up -- SQL in section 'Up' is executed when this migration is applied -- +micrate Down -- SQL section 'Down' is executed when this migration is rolled back
Comments that start with
+micrate are interpreted by micrate when running your migrations. In this case, the
Down directives are used to indicate which SQL statements must be run when applying or reverting a migration. You can now go along and write your migration like this:
-- +micrate Up CREATE TABLE users(id INT PRIMARY KEY, email VARCHAR NOT NULL); -- +micrate Down DROP TABLE users;
Now run it using
micrate up. This command will execute all pending migrations:
$ micrate up Migrating db, current version: 0, target: 20160524162947 OK 20160524162446_add_users_table.sql $ micrate dbversion # at any time you can find out the current version of the database 20160524162446
If you ever need to roll back the last migration, you can do so by executing
micrate down. There's also
micrate redo which rolls back the last migration and applies it again. Last but not least: use
micrate status to find out the state of each migration:
$ micrate status Applied At Migration ======================================= 2016-05-24 16:31:07 UTC -- 20160524162446_add_users_table.sql Pending -- 20160524163425_add_address_to_users.sql
If using complex statements that might contain semicolons, you must give micrate a hint on how to split the script into separate statements. You can do this with
StatementEnd directives: (thanks goose for this!)
-- +micrate Up -- +micrate StatementBegin CREATE OR REPLACE FUNCTION histories_partition_creation( DATE, DATE ) returns void AS $$ DECLARE create_query text; BEGIN FOR create_query IN SELECT 'CREATE TABLE IF NOT EXISTS histories_' || TO_CHAR( d, 'YYYY_MM' ) || ' ( CHECK( created_at >= timestamp ''' || TO_CHAR( d, 'YYYY-MM-DD 00:00:00' ) || ''' AND created_at < timestamp ''' || TO_CHAR( d + INTERVAL '1 month', 'YYYY-MM-DD 00:00:00' ) || ''' ) ) inherits ( histories );' FROM generate_series( $1, $2, '1 month' ) AS d LOOP EXECUTE create_query; END LOOP; -- LOOP END END; -- FUNCTION END $$ language plpgsql; -- +micrate StatementEnd
To use the Crystal API, add this to your application's
dependencies: micrate: github: amberframework/micrate
This allows you to programatically use micrate's features. You'll see the
Micrate module has an equivalent for every CLI command. If you need to use micrate's CLI without installing the tool (which could be convenient in a CI environment), you can write a runner script as follows:
#! /usr/bin/env crystal # # To build a standalone command line client, require the # driver you wish to use and use `Micrate::Cli`. # require "micrate" require "pg" Micrate::DB.connection_url = "postgresql://..." Micrate::Cli.run