PG Schema Migration

Simple schema migrations for PostgreSQL, which runs pure SQL. Inspired by Sequel and Cassandra Schema.

Installation

gem install pg-schema-migration

Usage

PG::Schema uses a DSL via the PG::Schema.migration method, a migration must have an up block with the changes you want to apply to the schema, and a down block reversing the change made by up.

A basic Migration

Use execute inside up and down blocks to run the queries that will modify the schema. Here is a fairly basic PG::Schema migration.

PG:Schema.migration do
  up do
    execute <<~SQL
      CREATE TABLE products (
        name VARCHAR(30),
        price NUMERIC
      )
    SQL
    
    execute "CREATE TRIGGER..."
  end
  
  down do
    execute "DROP TABLE products"
    execute "DROP TRIGGER..."
  end
end

If there is an error while running a migration, it will rollback the previous schema changes made by the migration.

Running migrations

require 'pg/schema-migration'
require 'pg'

@db = PG.connect(ENV.fetch("DATABASE_URL"))

PG::Schema.migration {...}
PG::Schema.migration {...}

migrator = PG::Schema::Migrator.new(
  db:        @db,                   # a PG connection
  directory: 'path/to/migrations',  # default: nil
  log:       Logger.new('/dev/nul') # default: Logger.new(STDOUT)
)

Migrate to the latest version

migrator.run!

Migrate to an specific version

migrator.run!(version: 1)

Migration files

PG::Schemas::Migrator expects that each migration file will be in a specific directory. For example:

PG::Schema::Migrator.new(db: @conn, directory: 'db/migrations').run!

PG::Schema::Migrator will look in the db/migrations folder relative to the current directory, and run unapplied migrations on the database.

The migration files must be specified as follows:

version_name.rb

where version is an integer and name is a string which should be a very brief description of what the migration does. Examples:

001_create_films.rb
002_add_director_to_films.rb
...
015_foo.rb
016_bar.rb

This guide is based on https://github.com/jeremyevans/sequel/blob/master/doc/migration.rdoc

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.