MediumArticle: Implementing rake db:* tasks in Non-Rails script (postgres, activerecord) https://medium.com/@AlexKalininHedin/rake-db-tasks-in-non-rails-application-95aa65509448

init_db.rb

#!/usr/bin/env ruby

require 'bundler'
Bundler.require(:default)
require 'active_support'
require 'active_record'
require 'pry'

@root_path = File.expand_path File.dirname(__FILE__)
@config = YAML.load_file(File.join(@root_path, 'config.yml'))

def drop_database
  cfg = @config['db']
  db_name = cfg['database']
  cfg['database'] = 'postgres'
  ActiveRecord::Base.establish_connection(cfg)

  sql_drop_connections_to_dp = <<-SQL
    SELECT pg_terminate_backend(pid)
    FROM pg_stat_activity
    WHERE datname = '#{ db_name }';
  SQL

  sql_dropdb = <<-SQL
    DROP DATABASE "#{ db_name }";
  SQL

  ActiveRecord::Base.connection.select_all sql_drop_connections_to_dp
  ActiveRecord::Base.connection.select_all sql_dropdb
  puts "Dropped database: #{ db_name }"
end

def create_database
  cfg = @config['db']
  db_name = cfg['database']
  cfg['database'] = 'postgres'
  ActiveRecord::Base.establish_connection(cfg)

  sql_createdb = <<-SQL
    CREATE DATABASE "#{ db_name }";
  SQL

  ActiveRecord::Base.connection.select_all sql_createdb
  puts "Created database #{db_name}"
end

def migrate_database
  cfg = @config['db']
  db_name = cfg['database']
  ActiveRecord::Base.establish_connection(cfg)

  puts "Migrating database #{db_name} ..."
  ActiveRecord::Migration.verbose = true
  ActiveRecord::Tasks::DatabaseTasks.migrate

  File.open('db/schema.rb', "w:utf-8") do |file|
    ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
  end
end

def rollback_database
  raise "Environment variable VERSION is required" if !ENV["VERSION"] || ENV["VERSION"].empty?

  cfg = @config['db']
  db_name = cfg['database']
  puts "Rolling back migration #{ ENV["VERSION"] } for database: #{db_name}..."
  ActiveRecord::Base.establish_connection(cfg)

  ActiveRecord::Tasks::DatabaseTasks.check_target_version

  ActiveRecord::Base.connection.migration_context.run(
      :down,
      ActiveRecord::Tasks::DatabaseTasks.target_version
  )
end

ALLOWED_ACTIONS = %w(drop create migrate recreate rollback).freeze
action = ALLOWED_ACTIONS.find {|e| e == ARGV[0]}
unless action
  help_msg = <<-TXT
    This is db helper. 
    
    USAGE:
    
      ruby init_db.rb <action>

        or

      VERSION=202004281342 ruby init_db.rb rollback
    
    OPTIONS:  
      possible <action>-s:
        drop - drop existing database
        crate - create new database
        migrate - migrate database
        recreate - drop,create,migrate
  
        rollback - rollback migration

    EXAMPLES: 
      ruby init_db.rb drop
      ruby init_db.rb create
      ruby init_db.rb migrate
      VERSION=202004281342 ruby init_db.rb rollback

  TXT

  puts help_msg.gsub('    ', '')
  abort
end

if action == 'drop'
  drop_database
elsif action == 'create'
  create_database
elsif action == 'migrate'
  migrate_database
elsif action == 'rollback'
  rollback_database
elsif action == 'recreate'
  drop_database
  create_database
  migrate_database
end