module ActiveRecord
class Migration
# <tt>ActiveRecord::Migration::CommandRecorder</tt> records commands done during
# a migration and knows how to reverse those commands. The CommandRecorder
# knows how to invert the following commands:
#
# * add_column
# * add_index
# * add_timestamps
# * create_table
# * create_join_table
# * remove_timestamps
# * rename_column
# * rename_index
# * rename_table
class CommandRecorder
ReversibleAndIrreversibleMethods = [:create_table, :create_join_table, :rename_table, :add_column, :remove_column,
:rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
:change_column_default, :add_reference, :remove_reference, :transaction,
:drop_join_table, :drop_table, :execute_block, :enable_extension,
:change_column, :execute, :remove_columns, :change_column_null,
:add_foreign_key, :remove_foreign_key
]
include JoinTable
attr_accessor :commands, :delegate, :reverting
def initialize(delegate = nil)
@commands = []
@delegate = delegate
@reverting = false
end
# While executing the given block, the recorded will be in reverting mode.
# All commands recorded will end up being recorded reverted
# and in reverse order.
# For example:
#
# recorder.revert{ recorder.record(:rename_table, [:old, :new]) }
# # same effect as recorder.record(:rename_table, [:new, :old])
def revert
@reverting = !@reverting
previous = @commands
@commands = []
yield
ensure
@commands = previous.concat(@commands.reverse)
@reverting = !@reverting
end
# record +command+. +command+ should be a method name and arguments.
# For example:
#
# recorder.record(:method_name, [:arg1, :arg2])
def record(*command, &block)
if @reverting
@commands << inverse_of(*command, &block)
else
@commands << (command << block)
end
end
# Returns the inverse of the given command. For example:
#
# recorder.inverse_of(:rename_table, [:old, :new])
# # => [:rename_table, [:new, :old]]
#
# This method will raise an +IrreversibleMigration+ exception if it cannot
# invert the +command+.
def inverse_of(command, args, &block)
method = :"invert_#{command}"
raise IrreversibleMigration, <<-MSG.strip_heredoc unless respond_to?(method, true)
This migration uses #{command} that is not automatically reversible.
There are two ways to mitigate this problem.
1. Define up and down methods instead of change method
2. Use reversible method in change method
MSG
send(method, args, &block)
end
def respond_to?(*args) # :nodoc:
super || delegate.respond_to?(*args)
end
ReversibleAndIrreversibleMethods.each do |method|
class_eval <<-EOV, __FILE__, __LINE__ + 1
def #{method}(*args, &block) # def create_table(*args, &block)
record(:"#{method}", args, &block) # record(:create_table, args, &block)
end # end
EOV
end
alias :add_belongs_to :add_reference
alias :remove_belongs_to :remove_reference
def change_table(table_name, options = {}) # :nodoc:
yield delegate.update_table_definition(table_name, self)
end
private
module StraightReversions
private
{ transaction: :transaction,
execute_block: :execute_block,
create_table: :drop_table,
create_join_table: :drop_join_table,
add_column: :remove_column,
add_timestamps: :remove_timestamps,
add_reference: :remove_reference,
enable_extension: :disable_extension
}.each do |cmd, inv|
[[inv, cmd], [cmd, inv]].uniq.each do |method, inverse|
class_eval <<-EOV, __FILE__, __LINE__ + 1
def invert_#{method}(args, &block) # def invert_create_table(args, &block)
[:#{inverse}, args, block] # [:drop_table, args, block]
end # end
EOV
end
end
end
include StraightReversions
def invert_drop_table(args, &block)
if args.size == 1 && block == nil
raise ActiveRecord::IrreversibleMigration, "To avoid mistakes, drop_table is only reversible if given options or a block (can be empty)."
end
super
end
def invert_rename_table(args)
[:rename_table, args.reverse]
end
def invert_remove_column(args)
raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
super
end
def invert_rename_index(args)
[:rename_index, [args.first] + args.last(2).reverse]
end
def invert_rename_column(args)
[:rename_column, [args.first] + args.last(2).reverse]
end
def invert_add_index(args)
table, columns, options = *args
options ||= {}
index_name = options[:name]
options_hash = index_name ? { name: index_name } : { column: columns }
[:remove_index, [table, options_hash]]
end
def invert_remove_index(args)
table, options_or_column = *args
if (options = options_or_column).is_a?(Hash)
unless options[:column]
raise ActiveRecord::IrreversibleMigration, "remove_index is only reversible if given a :column option."
end
options = options.dup
[:add_index, [table, options.delete(:column), options]]
elsif (column = options_or_column).present?
[:add_index, [table, column]]
end
end
alias :invert_add_belongs_to :invert_add_reference
alias :invert_remove_belongs_to :invert_remove_reference
def invert_change_column_default(args)
table, column, options = *args
unless options && options.is_a?(Hash) && options.has_key?(:from) && options.has_key?(:to)
raise ActiveRecord::IrreversibleMigration, "change_column_default is only reversible if given a :from and :to option."
end
[:change_column_default, [table, column, from: options[:to], to: options[:from]]]
end
def invert_change_column_null(args)
args[2] = !args[2]
[:change_column_null, args]
end
def invert_add_foreign_key(args)
from_table, to_table, add_options = args
add_options ||= {}
if add_options[:name]
options = { name: add_options[:name] }
elsif add_options[:column]
options = { column: add_options[:column] }
else
options = to_table
end
[:remove_foreign_key, [from_table, options]]
end
def invert_remove_foreign_key(args)
from_table, to_table, remove_options = args
raise ActiveRecord::IrreversibleMigration, "remove_foreign_key is only reversible if given a second table" if to_table.nil? || to_table.is_a?(Hash)
reversed_args = [from_table, to_table]
reversed_args << remove_options if remove_options
[:add_foreign_key, reversed_args]
end
# Forwards any missing method call to the \target.
def method_missing(method, *args, &block)
if @delegate.respond_to?(method)
@delegate.send(method, *args, &block)
else
super
end
end
end
end
end
