class ActiveRecord::Migration::CommandRecorder

Parent:: Object
Included modules:: ActiveRecord::Migration::CommandRecorder::StraightReversions

ActiveRecord::Migration::CommandRecorder 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

Attributes

commands[RW]

delegate[RW]

reverting[RW]

Public Class Methods

new(delegate = nil) Show source

# File activerecord/lib/active_record/migration/command_recorder.rb, line 21
def initialize(delegate = nil)
  @commands = []
  @delegate = delegate
  @reverting = false
end

Public Instance Methods

inverse_of(command, args, &block) Show source

# File activerecord/lib/active_record/migration/command_recorder.rb, line 63
def inverse_of(command, args, &block)
  method = :"invert_#{command}"
  raise IrreversibleMigration unless respond_to?(method, true)
  send(method, args, &block)
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.

record(*command, &block) Show source

# File activerecord/lib/active_record/migration/command_recorder.rb, line 48
def record(*command, &block)
  if @reverting
    @commands << inverse_of(*command, &block)
  else
    @commands << (command << block)
  end
end

record command. command should be a method name and arguments. For example:

recorder.record(:method_name, [:arg1, :arg2])

revert() { || ... } Show source

# File activerecord/lib/active_record/migration/command_recorder.rb, line 34
def revert
  @reverting = !@reverting
  previous = @commands
  @commands = []
  yield
ensure
  @commands = previous.concat(@commands.reverse)
  @reverting = !@reverting
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])