rebase migrations

migration.rake

namespace :migrations do
  DB_PATH = ActiveRecord::Migrator.migrations_path
  SEPARATOR = " --- "
  UPTO = ENV['upto']

  def run_command(command)
    %x(#{command}).tap do |result|
      status = $?
      unless status.success?
        raise "Command Error -- (#{status.exitstatus}): [#{command}]"
      end
      result
    end
  end

  def generate_schema_dump
    Rake::Task["db:schema:dump"].invoke
  end

  def run_migrations
    Rake::Task["db:migrate"].invoke
  end

  def ordinal_position_of_migration
    output = run_command("ls #{DB_PATH} | awk '{ print NR \"#{SEPARATOR}\" $0 }'")
    output.split("\n").
           map { |migration| migration.split(SEPARATOR) }.
           select { |migration| migration[1] =~ Regexp.new(UPTO) }.flatten.first
  end

  def remove_list_of_migrations
    upto = ordinal_position_of_migration
    run_command("ls #{DB_PATH}/* | head -n#{upto} | xargs rm -v")
  end

  def timestamp_of_migration
    File.basename(UPTO.split("_").first, ".rb")
  end

  def extract_schema_dump
    dump = StringIO.new
    ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, dump)

    dump.string.
         split("\n").
         reject { |line| line =~ /^ActiveRecord::Schema.define/ }.
         join("\n")
  end

  def indented_schema_dump(times)
    extract_schema_dump.split("\n").
                        map { |line| line.insert(0, " " * times) }.
                        join("\n")
  end

  def create_migration_file
    template = <<-EOS
class RebaseOldMigrations < ActiveRecord::Migration
  def change
#{indented_schema_dump(2)}
end
EOS

    file = timestamp_of_migration + "_rebase_old_migrations.rb"
    migration_file = File.join(DB_PATH, file)
    File.open(migration_file, 'w') { |mf| mf.write(template) }
  end

  desc "Squash/Rebase all migrations upto a certain point"
  task :squash do
    puts "* Generating schema dump..."
    generate_schema_dump

    puts "* Removing old migrations..."
    remove_list_of_migrations

    puts "* Creating squashed migration file..."
    create_migration_file

    puts "* Running the migrations as a sanity check..."
    run_migrations

    puts "* Done. See #{DB_PATH}."
  end

  task :rebase => :squash
end

upto="20120702125614_add_vetted_to_people.rb" rake migrations:rebase

upto="20120702125614_add_vetted_to_people.rb" rake migrations:squash

upto="20120702125614_add_vetted_to_people" rake migrations:rebase

upto="20120702125614" rake migrations:squash