class ActiveRecord::Migration::CommandRecorder

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:

Attributes

commands[RW]
delegate[RW]
reverting[RW]

Public Class Methods

new(delegate = nil) click to toggle source
# File 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) click to toggle source

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.

# File 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
record(*command, &block) click to toggle source

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

recorder.record(:method_name, [:arg1, :arg2])
# File 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
revert() { || ... } click to toggle source

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])
# File 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

Private Instance Methods

invert_add_foreign_key(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 172
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
invert_add_index(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 143
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
invert_change_column_null(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 167
def invert_change_column_null(args)
  args[2] = !args[2]
  [:change_column_null, args]
end
invert_drop_table(args, &block) click to toggle source
Calls superclass method
# File lib/active_record/migration/command_recorder.rb, line 119
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
invert_remove_column(args) click to toggle source
Calls superclass method
# File lib/active_record/migration/command_recorder.rb, line 130
def invert_remove_column(args)
  raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
  super
end
invert_remove_index(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 153
def invert_remove_index(args)
  table, options = *args

  unless options && options.is_a?(Hash) && 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]]
end
invert_rename_column(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 139
def invert_rename_column(args)
  [:rename_column, [args.first] + args.last(2).reverse]
end
invert_rename_index(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 135
def invert_rename_index(args)
  [:rename_index, [args.first] + args.last(2).reverse]
end
invert_rename_table(args) click to toggle source
# File lib/active_record/migration/command_recorder.rb, line 126
def invert_rename_table(args)
  [:rename_table, args.reverse]
end
method_missing(method, *args, &block) click to toggle source

Forwards any missing method call to the target.

Calls superclass method
# File lib/active_record/migration/command_recorder.rb, line 188
def method_missing(method, *args, &block)
  if @delegate.respond_to?(method)
    @delegate.send(method, *args, &block)
  else
    super
  end
end