migrate_sql.rake

# Generates SQL from migrations
#
# Usage:
#   rake db:[migrate,rollback]:with_sql
#
# The previous rake task will run migrations and create a file in `db/migrate_sql`
# Depending on migrate or rollback a file will be created with the respective
# sufix.
#
# Drawbacks:
#   - There is no way to automatically generate migrate and rollback SQL at once
#   If we need to generate a SQL from migrations its necessary to rollback:with_sql
#   to the desired version and then migrate:with_sql
#
namespace :db do
  %i(migrate rollback).each do |n|
    namespace n do |migration_task|
      desc 'Run migration, and generated SQL'
      task with_sql: :environment do
        # Fetch action, migrate or rollback
        parent_task = Rake.application.top_level_tasks.first.scan(/\w*\:(\w*)\:/).flatten.first

        migrate_sql_path = Pathname "#{Rails.root}/db/migrate_sql"
        MIGRATE_SQL_FILE_PATH = Pathname "#{migrate_sql_path}/#{Time.now.strftime('%Y%m%d%H%M')}_#{parent_task}.sql"

        Dir.mkdir migrate_sql_path unless migrate_sql_path.exist?

        ActiveRecord::Base.connection.class.class_eval do
          alias :original_execute :execute

          # Define our own execute
          def execute(sql, name = nil)
            # Check for some DDL and DML statements in order to avoid AR check
            # queries like SHOW statements
            if /^(create|alter|drop|insert|delete|update)/i.match sql
              File.open(MIGRATE_SQL_FILE_PATH, 'a') { |f| f.puts "#{sql};\n" }
            end

            original_execute sql, name
          end
        end

        migrations = ActiveRecord::Migrator.migrations("#{Rails.root}/db/migrate").map(&:name)
        current_position = migrations.index ActiveRecord::Migrator.last_migration.name

        # Add migration metainformation
        File.open(MIGRATE_SQL_FILE_PATH, 'w') do |f|
          f.puts "-- Script created @ #{Time.now}"
          f.puts "-- Included Migrations: #{migrations[current_position..-1].to_sentence}"
        end

        # Invoke the normal migration procedure now
        Rake::Task["db:#{parent_task}"].invoke

        puts "Ran #{parent_task} and wrote sql to #{MIGRATE_SQL_FILE_PATH}"
      end
    end
  end
end