diff options
Diffstat (limited to 'activerecord')
-rw-r--r-- | activerecord/lib/active_record/migration.rb | 72 | ||||
-rw-r--r-- | activerecord/lib/active_record/migration/command_recorder.rb | 7 |
2 files changed, 77 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb index b4dd8eff5a..112d52024f 100644 --- a/activerecord/lib/active_record/migration.rb +++ b/activerecord/lib/active_record/migration.rb @@ -9,7 +9,77 @@ module ActiveRecord end end - # Exception that can be raised to stop migrations from going backwards. + # Exception that can be raised to stop migrations from being rolled back. + # For example the following migration is not reversible. + # Rolling back this migration will raise an ActiveRecord::IrreversibleMigration error. + # + # class IrreversibleMigrationExample < ActiveRecord::Migration + # def change + # create_table :distributors do |t| + # t.string :zipcode + # end + # + # execute <<-SQL + # ALTER TABLE distributors + # ADD CONSTRAINT zipchk + # CHECK (char_length(zipcode) = 5) NO INHERIT; + # SQL + # end + # end + # + # There are two ways to mitigate this problem. + # + # 1. Define <tt>#up</tt> and <tt>#down</tt> methods instead of <tt>#change</tt>: + # + # class ReversibleMigrationExample < ActiveRecord::Migration + # def up + # create_table :distributors do |t| + # t.string :zipcode + # end + # + # execute <<-SQL + # ALTER TABLE distributors + # ADD CONSTRAINT zipchk + # CHECK (char_length(zipcode) = 5) NO INHERIT; + # SQL + # end + # + # def down + # execute <<-SQL + # ALTER TABLE distributors + # DROP CONSTRAINT zipchk + # SQL + # + # drop_table :distributors + # end + # end + # + # 2. Use the #reversible method in <tt>#change</tt> method: + # + # class ReversibleMigrationExample < ActiveRecord::Migration + # def change + # create_table :distributors do |t| + # t.string :zipcode + # end + # + # reversible do |dir| + # dir.up do + # execute <<-SQL + # ALTER TABLE distributors + # ADD CONSTRAINT zipchk + # CHECK (char_length(zipcode) = 5) NO INHERIT; + # SQL + # end + # + # dir.down do + # execute <<-SQL + # ALTER TABLE distributors + # DROP CONSTRAINT zipchk + # SQL + # end + # end + # end + # end class IrreversibleMigration < MigrationError end diff --git a/activerecord/lib/active_record/migration/command_recorder.rb b/activerecord/lib/active_record/migration/command_recorder.rb index 3ab0f28c9b..4c4afb4dbd 100644 --- a/activerecord/lib/active_record/migration/command_recorder.rb +++ b/activerecord/lib/active_record/migration/command_recorder.rb @@ -81,7 +81,12 @@ module ActiveRecord # invert the +command+. def inverse_of(command, args, &block) method = :"invert_#{command}" - raise IrreversibleMigration unless respond_to?(method, true) + raise IrreversibleMigration, <<-MSG.strip_heredoc unless respond_to?(method, true) + 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. + MSG send(method, args, &block) end |