module ActiveRecord
class IrreversibleMigration < ActiveRecordError#:nodoc:
end
class DuplicateMigrationVersionError < ActiveRecordError#:nodoc:
def initialize(version)
super("Multiple migrations have the version number #{version}")
end
end
class UnknownMigrationVersionError < ActiveRecordError #:nodoc:
def initialize(version)
super("No migration with version number #{version}")
end
end
class IllegalMigrationNameError < ActiveRecordError#:nodoc:
def initialize(name)
super("Illegal name for migration file: #{name}\n\t(only lower case letters, numbers, and '_' allowed)")
end
end
# Migrations can manage the evolution of a schema used by several physical databases. It's a solution
# to the common problem of adding a field to make a new feature work in your local database, but being unsure of how to
# push that change to other developers and to the production server. With migrations, you can describe the transformations
# in self-contained classes that can be checked into version control systems and executed against another database that
# might be one, two, or five versions behind.
#
# Example of a simple migration:
#
# class AddSsl < ActiveRecord::Migration
# def self.up
# add_column :accounts, :ssl_enabled, :boolean, :default => 1
# end
#
# def self.down
# remove_column :accounts, :ssl_enabled
# end
# end
#
# This migration will add a boolean flag to the accounts table and remove it if you're backing out of the migration.
# It shows how all migrations have two class methods +up+ and +down+ that describes the transformations required to implement
# or remove the migration. These methods can consist of both the migration specific methods like add_column and remove_column,
# but may also contain regular Ruby code for generating data needed for the transformations.
#
# Example of a more complex migration that also needs to initialize data:
#
# class AddSystemSettings < ActiveRecord::Migration
# def self.up
# create_table :system_settings do |t|
# t.string :name
# t.string :label
# t.text :value
# t.string :type
# t.integer :position
# end
#
# SystemSetting.create :name => "notice", :label => "Use notice?", :value => 1
# end
#
# def self.down
# drop_table :system_settings
# end
# end
#
# This migration first adds the system_settings table, then creates the very first row in it using the Active Record model
# that relies on the table. It also uses the more advanced create_table syntax where you can specify a complete table schema
# in one block call.
#
# == Available transformations
#
# * <tt>create_table(name, options)</tt> Creates a table called +name+ and makes the table object available to a block
# that can then add columns to it, following the same format as add_column. See example above. The options hash is for
# fragments like "DEFAULT CHARSET=UTF-8" that are appended to the create table definition.
# * <tt>drop_table(name)</tt>: Drops the table called +name+.
# * <tt>rename_table(old_name, new_name)</tt>: Renames the table called +old_name+ to +new_name+.
# * <tt>add_column(table_name, column_name, type, options)</tt>: Adds a new column to the table called +table_name+
# named +column_name+ specified to be one of the following types:
# :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time,
# :date, :binary, :boolean. A default value can be specified by passing an
# +options+ hash like { :default => 11 }. Other options include :limit and :null (e.g. { :limit => 50, :null => false })
# -- see ActiveRecord::ConnectionAdapters::TableDefinition#column for details.
# * <tt>rename_column(table_name, column_name, new_column_name)</tt>: Renames a column but keeps the type and content.
# * <tt>change_column(table_name, column_name, type, options)</tt>: Changes the column to a different type using the same
# parameters as add_column.
# * <tt>remove_column(table_name, column_name)</tt>: Removes the column named +column_name+ from the table called +table_name+.
# * <tt>add_index(table_name, column_names, options)</tt>: Adds a new index with the name of the column. Other options include
# :name and :unique (e.g. { :name => "users_name_index", :unique => true }).
# * <tt>remove_index(table_name, index_name)</tt>: Removes the index specified by +index_name+.
#
# == Irreversible transformations
#
# Some transformations are destructive in a manner that cannot be reversed. Migrations of that kind should raise
# an <tt>ActiveRecord::IrreversibleMigration</tt> exception in their +down+ method.
#
# == Running migrations from within Rails
#
# The Rails package has several tools to help create and apply migrations.
#
# To generate a new migration, you can use
# script/generate migration MyNewMigration
#
# where MyNewMigration is the name of your migration. The generator will
# create an empty migration file <tt>nnn_my_new_migration.rb</tt> in the <tt>db/migrate/</tt>
# directory where <tt>nnn</tt> is the next largest migration number.
#
# You may then edit the <tt>self.up</tt> and <tt>self.down</tt> methods of
# MyNewMigration.
#
# There is a special syntactic shortcut to generate migrations that add fields to a table.
# script/generate migration add_fieldname_to_tablename fieldname:string
#
# This will generate the file <tt>nnn_add_fieldname_to_tablename</tt>, which will look like this:
# class AddFieldnameToTablename < ActiveRecord::Migration
# def self.up
# add_column :tablenames, :fieldname, :string
# end
#
# def self.down
# remove_column :tablenames, :fieldname
# end
# end
#
# To run migrations against the currently configured database, use
# <tt>rake db:migrate</tt>. This will update the database by running all of the
# pending migrations, creating the <tt>schema_info</tt> table if missing.
#
# To roll the database back to a previous migration version, use
# <tt>rake db:migrate VERSION=X</tt> where <tt>X</tt> is the version to which
# you wish to downgrade. If any of the migrations throw an
# <tt>ActiveRecord::IrreversibleMigration</tt> exception, that step will fail and you'll
# have some manual work to do.
#
# == Database support
#
# Migrations are currently supported in MySQL, PostgreSQL, SQLite,
# SQL Server, Sybase, and Oracle (all supported databases except DB2).
#
# == More examples
#
# Not all migrations change the schema. Some just fix the data:
#
# class RemoveEmptyTags < ActiveRecord::Migration
# def self.up
# Tag.find(:all).each { |tag| tag.destroy if tag.pages.empty? }
# end
#
# def self.down
# # not much we can do to restore deleted data
# raise ActiveRecord::IrreversibleMigration, "Can't recover the deleted tags"
# end
# end
#
# Others remove columns when they migrate up instead of down:
#
# class RemoveUnnecessaryItemAttributes < ActiveRecord::Migration
# def self.up
# remove_column :items, :incomplete_items_count
# remove_column :items, :completed_items_count
# end
#
# def self.down
# add_column :items, :incomplete_items_count
# add_column :items, :completed_items_count
# end
# end
#
# And sometimes you need to do something in SQL not abstracted directly by migrations:
#
# class MakeJoinUnique < ActiveRecord::Migration
# def self.up
# execute "ALTER TABLE `pages_linked_pages` ADD UNIQUE `page_id_linked_page_id` (`page_id`,`linked_page_id`)"
# end
#
# def self.down
# execute "ALTER TABLE `pages_linked_pages` DROP INDEX `page_id_linked_page_id`"
# end
# end
#
# == Using a model after changing its table
#
# Sometimes you'll want to add a column in a migration and populate it immediately after. In that case, you'll need
# to make a call to Base#reset_column_information in order to ensure that the model has the latest column data from
# after the new column was added. Example:
#
# class AddPeopleSalary < ActiveRecord::Migration
# def self.up
# add_column :people, :salary, :integer
# Person.reset_column_information
# Person.find(:all).each do |p|
# p.update_attribute :salary, SalaryCalculator.compute(p)
# end
# end
# end
#
# == Controlling verbosity
#
# By default, migrations will describe the actions they are taking, writing
# them to the console as they happen, along with benchmarks describing how
# long each step took.
#
# You can quiet them down by setting ActiveRecord::Migration.verbose = false.
#
# You can also insert your own messages and benchmarks by using the #say_with_time
# method:
#
# def self.up
# ...
# say_with_time "Updating salaries..." do
# Person.find(:all).each do |p|
# p.update_attribute :salary, SalaryCalculator.compute(p)
# end
# end
# ...
# end
#
# The phrase "Updating salaries..." would then be printed, along with the
# benchmark for the block when the block completes.
class Migration
@@verbose = true
cattr_accessor :verbose
class << self
def up_with_benchmarks #:nodoc:
migrate(:up)
end
def down_with_benchmarks #:nodoc:
migrate(:down)
end
# Execute this migration in the named direction
def migrate(direction)
return unless respond_to?(direction)
case direction
when :up then announce "migrating"
when :down then announce "reverting"
end
result = nil
time = Benchmark.measure { result = send("#{direction}_without_benchmarks") }
case direction
when :up then announce "migrated (%.4fs)" % time.real; write
when :down then announce "reverted (%.4fs)" % time.real; write
end
result
end
# Because the method added may do an alias_method, it can be invoked
# recursively. We use @ignore_new_methods as a guard to indicate whether
# it is safe for the call to proceed.
def singleton_method_added(sym) #:nodoc:
return if defined?(@ignore_new_methods) && @ignore_new_methods
begin
@ignore_new_methods = true
case sym
when :up, :down
klass = (class << self; self; end)
klass.send(:alias_method_chain, sym, "benchmarks")
end
ensure
@ignore_new_methods = false
end
end
def write(text="")
puts(text) if verbose
end
def announce(message)
text = "#{@version} #{name}: #{message}"
length = [0, 75 - text.length].max
write "== %s %s" % [text, "=" * length]
end
def say(message, subitem=false)
write "#{subitem ? " ->" : "--"} #{message}"
end
def say_with_time(message)
say(message)
result = nil
time = Benchmark.measure { result = yield }
say "%.4fs" % time.real, :subitem
say("#{result} rows", :subitem) if result.is_a?(Integer)
result
end
def suppress_messages
save, self.verbose = verbose, false
yield
ensure
self.verbose = save
end
def method_missing(method, *arguments, &block)
arg_list = arguments.map(&:inspect) * ', '
say_with_time "#{method}(#{arg_list})" do
unless arguments.empty? || method == :execute
arguments[0] = Migrator.proper_table_name(arguments.first)
end
ActiveRecord::Base.connection.send(method, *arguments, &block)
end
end
end
end
class Migrator#:nodoc:
class << self
def migrate(migrations_path, target_version = nil)
case
when target_version.nil?, current_version < target_version
up(migrations_path, target_version)
when current_version > target_version
down(migrations_path, target_version)
when current_version == target_version
return # You're on the right version
end
end
def rollback(migrations_path, steps=1)
migrator = self.new(:down, migrations_path)
start_index = migrator.migrations.index(migrator.current_migration)
return unless start_index
finish = migrator.migrations[start_index + steps]
down(migrations_path, finish ? finish.version : 0)
end
def up(migrations_path, target_version = nil)
self.new(:up, migrations_path, target_version).migrate
end
def down(migrations_path, target_version = nil)
self.new(:down, migrations_path, target_version).migrate
end
def run(direction, migrations_path, target_version)
self.new(direction, migrations_path, target_version).run
end
def schema_info_table_name
Base.table_name_prefix + "schema_info" + Base.table_name_suffix
end
def current_version
Base.connection.select_value("SELECT version FROM #{schema_info_table_name}").to_i
end
def proper_table_name(name)
# Use the ActiveRecord objects own table_name, or pre/suffix from ActiveRecord::Base if name is a symbol/string
name.table_name rescue "#{ActiveRecord::Base.table_name_prefix}#{name}#{ActiveRecord::Base.table_name_suffix}"
end
end
def initialize(direction, migrations_path, target_version = nil)
raise StandardError.new("This database does not yet support migrations") unless Base.connection.supports_migrations?
Base.connection.initialize_schema_information
@direction, @migrations_path, @target_version = direction, migrations_path, target_version
end
def current_version
self.class.current_version
end
def current_migration
migrations.detect { |m| m.version == current_version }
end
def run
target = migrations.detect { |m| m.version == @target_version }
raise UnknownMigrationVersionError.new(@target_version) if target.nil?
target.migrate(@direction)
end
def migrate
current = migrations.detect { |m| m.version == current_version }
target = migrations.detect { |m| m.version == @target_version }
if target.nil? && !@target_version.nil? && @target_version > 0
raise UnknownMigrationVersionError.new(@target_version)
end
start = migrations.index(current) || 0
finish = migrations.index(target) || migrations.size - 1
runnable = migrations[start..finish]
# skip the current migration if we're heading upwards
runnable.shift if up? && runnable.first == current
# skip the last migration if we're headed down, but not ALL the way down
runnable.pop if down? && !target.nil?
runnable.each do |migration|
Base.logger.info "Migrating to #{migration} (#{migration.version})"
migration.migrate(@direction)
set_schema_version_after_migrating(migration)
end
end
def migrations
@migrations ||= begin
files = Dir["#{@migrations_path}/[0-9]*_*.rb"]
migrations = files.inject([]) do |klasses, file|
version, name = file.scan(/([0-9]+)_([_a-z0-9]*).rb/).first
raise IllegalMigrationNameError.new(f) unless version
version = version.to_i
if klasses.detect { |m| m.version == version }
raise DuplicateMigrationVersionError.new(version)
end
load(file)
klasses << returning(name.camelize.constantize) do |klass|
class << klass; attr_accessor :version end
klass.version = version
end
end
migrations = migrations.sort_by(&:version)
down? ? migrations.reverse : migrations
end
end
def pending_migrations
migrations.select { |m| m.version > current_version }
end
private
def set_schema_version_after_migrating(migration)
version = migration.version
if down?
after = migrations[migrations.index(migration) + 1]
version = after ? after.version : 0
end
Base.connection.update("UPDATE #{self.class.schema_info_table_name} SET version = #{version}")
end
def up?
@direction == :up
end
def down?
@direction == :down
end
end
end
