class ActiveRecord::Migration::CommandRecorder

invert the +command+.
This method will raise an +IrreversibleMigration+ exception if it cannot

# => [[:add_column, :some_table, :foo, :string], [:add_column, :some_table, :bar, :string]]
recorder.inverse_of(:remove_columns, [:some_table, :foo, :bar, type: :string])

If the inverse of a command requires several commands, returns array of commands.

# => [:rename_table, [:new, :old]]
recorder.inverse_of(:rename_table, [:old, :new])

Returns the inverse of the given command. For example:

def inverse_of(command, args, &block)
  method = :"invert_#{command}"
  raise IrreversibleMigration, <<~MSG unless respond_to?(method, true)
    This migration uses #{command}, which is not automatically reversible.
    To make the migration reversible you can either:
    1. Define #up and #down methods in place of the #change method.
    2. Use the #reversible method to define reversible behavior.
  MSG
  send(method, args, &block)
end