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authoryui-knk <spiketeika@gmail.com>2015-08-29 17:15:11 +0900
committeryui-knk <spiketeika@gmail.com>2015-08-29 17:15:11 +0900
commitbef377c666d54719ec8bd58979da55fd48cb5dfd (patch)
treeb0b471007dd84efe7912a10cde7174d3cf0fa6ba
parentf13d31c37c93cabdb61c1de010af6ad134e2ec6f (diff)
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[ci skip] Add comments for `IrreversibleMigration`
-rw-r--r--activerecord/lib/active_record/migration.rb70
1 files changed, 70 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 4901f9dafd..93e7a04f55 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -10,6 +10,76 @@ module ActiveRecord
end
# Exception that can be raised to stop migrations from going backwards.
+ # For example <tt>IrreversibleMigrationExample</tt> is not reversible.
+ # When you rollback this migration, <tt>ActiveRecord::IrreversibleMigration</tt> is raised.
+ #
+ # 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. Use <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 <tt>reversible</tt> 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