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Diffstat (limited to 'guides/source/active_record_migrations.md')
-rw-r--r-- | guides/source/active_record_migrations.md | 52 |
1 files changed, 32 insertions, 20 deletions
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md index 980dfe6953..67881e6087 100644 --- a/guides/source/active_record_migrations.md +++ b/guides/source/active_record_migrations.md @@ -522,20 +522,27 @@ majority of cases, where Active Record knows how to reverse the migration automatically. Currently, the `change` method supports only these migration definitions: -* `add_column` -* `add_index` -* `add_reference` -* `add_timestamps` -* `add_foreign_key` -* `create_table` -* `create_join_table` -* `drop_table` (must supply a block) -* `drop_join_table` (must supply a block) -* `remove_timestamps` -* `rename_column` -* `rename_index` -* `remove_reference` -* `rename_table` +* add_column +* add_foreign_key +* add_index +* add_reference +* add_timestamps +* 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_foreign_key (must supply a second table) +* remove_index +* remove_reference +* remove_timestamps +* rename_column +* rename_index +* rename_table `change_table` is also reversible, as long as the block does not call `change`, `change_default` or `remove`. @@ -652,7 +659,7 @@ can't be done. You can use Active Record's ability to rollback migrations using the `revert` method: ```ruby -require_relative '2012121212_example_migration' +require_relative '20121212123456_example_migration' class FixupExampleMigration < ActiveRecord::Migration def change @@ -782,7 +789,7 @@ The `rake db:reset` task will drop the database and set it up again. This is functionally equivalent to `rake db:drop db:setup`. NOTE: This is not the same as running all the migrations. It will only use the -contents of the current `schema.rb` file. If a migration can't be rolled back, +contents of the current `db/schema.rb` or `db/structure.sql` file. If a migration can't be rolled back, `rake db:reset` may not help you. To find out more about dumping the schema see [Schema Dumping and You](#schema-dumping-and-you) section. @@ -1004,7 +1011,10 @@ such features, the `execute` method can be used to execute arbitrary SQL. Migrations and Seed Data ------------------------ -Some people use migrations to add data to the database: +The main purpose of Rails' migration feature is to issue commands that modify the +schema using a consistent process. Migrations can also be used +to add or modify data. This is useful in an existing database that can't be destroyed +and recreated, such as a production database. ```ruby class AddInitialProducts < ActiveRecord::Migration @@ -1020,9 +1030,11 @@ class AddInitialProducts < ActiveRecord::Migration end ``` -However, Rails has a 'seeds' feature that should be used for seeding a database -with initial data. It's a really simple feature: just fill up `db/seeds.rb` -with some Ruby code, and run `rake db:seed`: +To add initial data after a database is created, Rails has a built-in +'seeds' feature that makes the process quick and easy. This is especially +useful when reloading the database frequently in development and test environments. +It's easy to get started with this feature: just fill up `db/seeds.rb` with some +Ruby code, and run `rake db:seed`: ```ruby 5.times do |i| |