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_foreign_key
add_index
add_reference
add_timestamps
change_column
change_column_default (must supply a :from and :to option)
change_column_null
create_join_table
create_table
disable_extension
drop_join_table
drop_table (must supply a block)
enable_extension
remove_column (must supply a type)
remove_columns (must specify at least one column name or more)
remove_foreign_key (must supply a second table)
remove_index
remove_reference
remove_timestamps
rename_column
rename_index
rename_table
# File activerecord/lib/active_record/migration/command_recorder.rb, line 42 def initialize(delegate = nil) @commands = [] @delegate = delegate @reverting = false 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 activerecord/lib/active_record/migration/command_recorder.rb, line 84 def inverse_of(command, args, &block) method = :"invert_#{command}" raise IrreversibleMigration, " 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. ".strip_heredoc 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 activerecord/lib/active_record/migration/command_recorder.rb, line 69 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 activerecord/lib/active_record/migration/command_recorder.rb, line 55 def revert @reverting = !@reverting previous = @commands @commands = [] yield ensure @commands = previous.concat(@commands.reverse) @reverting = !@reverting end
© 2004–2017 David Heinemeier Hansson
Licensed under the MIT License.