module ActiveRecord
class Migration
# 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_timestamp
# * create_table
# * remove_timestamps
# * rename_column
# * rename_index
# * rename_table
class CommandRecorder
attr_accessor :commands, :delegate
def initialize(delegate = nil)
@commands = []
@delegate = delegate
end
# record +command+. +command+ should be a method name and arguments.
# For example:
#
# recorder.record(:method_name, [:arg1, arg2])
def record(*command)
@commands << command
end
# Returns a list that represents commands that are the inverse of the
# commands stored in +commands+. For example:
#
# recorder.record(:rename_table, [:old, :new])
# recorder.inverse # => [:rename_table, [:new, :old]]
#
# This method will raise an IrreversibleMigration exception if it cannot
# invert the +commands+.
def inverse
@commands.reverse.map { |name, args|
method = :"invert_#{name}"
raise IrreversibleMigration unless respond_to?(method, true)
send(method, args)
}
end
def respond_to?(*args) # :nodoc:
super || delegate.respond_to?(*args)
end
[:create_table, :rename_table, :add_column, :remove_column, :rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps, :change_column, :change_column_default].each do |method|
class_eval <<-EOV, __FILE__, __LINE__ + 1
def #{method}(*args)
record(:"#{method}", args)
end
EOV
end
private
def invert_create_table(args)
[:drop_table, args]
end
def invert_rename_table(args)
[:rename_table, args.reverse]
end
def invert_add_column(args)
[:remove_column, args.first(2)]
end
def invert_rename_index(args)
[:rename_index, args.reverse]
end
def invert_rename_column(args)
[:rename_column, [args.first] + args.last(2).reverse]
end
def invert_add_index(args)
table, columns, _ = *args
[:remove_index, [table, {:column => columns}]]
end
def invert_remove_timestamps(args)
[:add_timestamps, args]
end
def invert_add_timestamps(args)
[:remove_timestamps, args]
end
# Forwards any missing method call to the \target.
def method_missing(method, *args, &block)
@delegate.send(method, *args, &block)
rescue NoMethodError => e
raise e, e.message.sub(/ for #<.*$/, " via proxy for #{@delegate}")
end
end
end
end
