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module ActiveRecord
class Migration
# <tt>ActiveRecord::Migration::CommandRecorder</tt> 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
class CommandRecorder
include JoinTable
attr_accessor :commands, :delegate, :reverting
def initialize(delegate = nil)
@commands = []
@delegate = delegate
@reverting = false
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])
def revert
@reverting = !@reverting
previous = @commands
@commands = []
yield
ensure
@commands = previous.concat(@commands.reverse)
@reverting = !@reverting
end
# record +command+. +command+ should be a method name and arguments.
# For example:
#
# recorder.record(:method_name, [:arg1, :arg2])
def record(*command, &block)
if @reverting
@commands << inverse_of(*command, &block)
else
@commands << (command << block)
end
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+.
def inverse_of(command, args, &block)
method = :"invert_#{command}"
raise IrreversibleMigration unless respond_to?(method, true)
send(method, args, &block)
end
def respond_to?(*args) # :nodoc:
super || delegate.respond_to?(*args)
end
[:create_table, :create_join_table, :rename_table, :add_column, :remove_column,
:rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
:change_column_default, :add_reference, :remove_reference, :transaction,
:drop_join_table, :drop_table, :execute_block,
:change_column, :execute, :remove_columns, # irreversible methods need to be here too
].each do |method|
class_eval <<-EOV, __FILE__, __LINE__ + 1
def #{method}(*args, &block) # def create_table(*args, &block)
record(:"#{method}", args, &block) # record(:create_table, args, &block)
end # end
EOV
end
alias :add_belongs_to :add_reference
alias :remove_belongs_to :remove_reference
def change_table(table_name, options = {})
yield ConnectionAdapters::Table.new(table_name, self)
end
private
module StraightReversions
private
{ transaction: :transaction,
execute_block: :execute_block,
create_table: :drop_table,
create_join_table: :drop_join_table,
add_column: :remove_column,
add_timestamps: :remove_timestamps,
add_reference: :remove_reference,
}.each do |cmd, inv|
[[inv, cmd], [cmd, inv]].uniq.each do |method, inverse|
class_eval <<-EOV, __FILE__, __LINE__ + 1
def invert_#{method}(args, &block) # def invert_create_table(args, &block)
[:#{inverse}, args, block] # [:drop_table, args, block]
end # end
EOV
end
end
end
include StraightReversions
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
def invert_rename_table(args)
[:rename_table, args.reverse]
end
def invert_remove_column(args)
raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
super
end
def invert_rename_index(args)
[:rename_index, [args.first] + args.last(2).reverse]
end
def invert_rename_column(args)
[:rename_column, [args.first] + args.last(2).reverse]
end
def invert_add_index(args)
table, columns, options = *args
[:remove_index, [table, (options || {}).merge(column: columns)]]
end
def invert_remove_index(args)
table, options = *args
raise ActiveRecord::IrreversibleMigration, "remove_index is only reversible if given a :column option." unless options && options[:column]
options = options.dup
[:add_index, [table, options.delete(:column), options]]
end
alias :invert_add_belongs_to :invert_add_reference
alias :invert_remove_belongs_to :invert_remove_reference
# 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
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