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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
def send(method, *args) # :nodoc:
return super unless respond_to?(method)
record(method, args)
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
end
end
end
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