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_timestamps
create_table
create_join_table
remove_timestamps
rename_column
rename_index
rename_table
# File lib/active_record/migration/command_recorder.rb, line 21 def initialize(delegate = nil) @commands = [] @delegate = delegate @reverting = false end
# File lib/active_record/migration/command_recorder.rb, line 88 def change_table(table_name, options = {}) yield ConnectionAdapters::Table.new(table_name, self) 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
.
# 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
. 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
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
# File lib/active_record/migration/command_recorder.rb, line 140 def invert_add_index(args) table, columns, options = *args [:remove_index, [table, (options || {}).merge(column: columns)]] end
# File lib/active_record/migration/command_recorder.rb, line 116 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
# File lib/active_record/migration/command_recorder.rb, line 127 def invert_remove_column(args) raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2 super end
# File lib/active_record/migration/command_recorder.rb, line 145 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
# File lib/active_record/migration/command_recorder.rb, line 136 def invert_rename_column(args) [:rename_column, [args.first] + args.last(2).reverse] end
# File lib/active_record/migration/command_recorder.rb, line 132 def invert_rename_index(args) [:rename_index, [args.first] + args.last(2).reverse] end
# File lib/active_record/migration/command_recorder.rb, line 123 def invert_rename_table(args) [:rename_table, args.reverse] end
Forwards any missing method call to the target.
# File lib/active_record/migration/command_recorder.rb, line 160 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