395 lines
15 KiB
Ruby
395 lines
15 KiB
Ruby
module ActiveRecord
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class IrreversibleMigration < ActiveRecordError#:nodoc:
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end
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class DuplicateMigrationVersionError < ActiveRecordError#:nodoc:
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def initialize(version)
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super("Multiple migrations have the version number #{version}")
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end
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end
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# Migrations can manage the evolution of a schema used by several physical databases. It's a solution
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# to the common problem of adding a field to make a new feature work in your local database, but being unsure of how to
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# push that change to other developers and to the production server. With migrations, you can describe the transformations
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# in self-contained classes that can be checked into version control systems and executed against another database that
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# might be one, two, or five versions behind.
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#
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# Example of a simple migration:
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#
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# class AddSsl < ActiveRecord::Migration
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# def self.up
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# add_column :accounts, :ssl_enabled, :boolean, :default => 1
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# end
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#
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# def self.down
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# remove_column :accounts, :ssl_enabled
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# end
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# end
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#
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# This migration will add a boolean flag to the accounts table and remove it again, if you're backing out of the migration.
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# It shows how all migrations have two class methods +up+ and +down+ that describes the transformations required to implement
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# or remove the migration. These methods can consist of both the migration specific methods, like add_column and remove_column,
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# but may also contain regular Ruby code for generating data needed for the transformations.
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#
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# Example of a more complex migration that also needs to initialize data:
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#
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# class AddSystemSettings < ActiveRecord::Migration
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# def self.up
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# create_table :system_settings do |t|
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# t.column :name, :string
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# t.column :label, :string
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# t.column :value, :text
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# t.column :type, :string
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# t.column :position, :integer
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# end
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#
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# SystemSetting.create :name => "notice", :label => "Use notice?", :value => 1
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# end
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#
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# def self.down
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# drop_table :system_settings
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# end
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# end
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#
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# This migration first adds the system_settings table, then creates the very first row in it using the Active Record model
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# that relies on the table. It also uses the more advanced create_table syntax where you can specify a complete table schema
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# in one block call.
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#
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# == Available transformations
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#
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# * <tt>create_table(name, options)</tt> Creates a table called +name+ and makes the table object available to a block
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# that can then add columns to it, following the same format as add_column. See example above. The options hash is for
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# fragments like "DEFAULT CHARSET=UTF-8" that are appended to the create table definition.
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# * <tt>drop_table(name)</tt>: Drops the table called +name+.
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# * <tt>rename_table(old_name, new_name)</tt>: Renames the table called +old_name+ to +new_name+.
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# * <tt>add_column(table_name, column_name, type, options)</tt>: Adds a new column to the table called +table_name+
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# named +column_name+ specified to be one of the following types:
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# :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time,
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# :date, :binary, :boolean. A default value can be specified by passing an
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# +options+ hash like { :default => 11 }. Other options include :limit and :null (e.g. { :limit => 50, :null => false })
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# -- see ActiveRecord::ConnectionAdapters::TableDefinition#column for details.
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# * <tt>rename_column(table_name, column_name, new_column_name)</tt>: Renames a column but keeps the type and content.
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# * <tt>change_column(table_name, column_name, type, options)</tt>: Changes the column to a different type using the same
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# parameters as add_column.
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# * <tt>remove_column(table_name, column_name)</tt>: Removes the column named +column_name+ from the table called +table_name+.
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# * <tt>add_index(table_name, column_names, index_type, index_name)</tt>: Add a new index with the name of the column, or +index_name+ (if specified) on the column(s). Specify an optional +index_type+ (e.g. UNIQUE).
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# * <tt>remove_index(table_name, index_name)</tt>: Remove the index specified by +index_name+.
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#
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# == Irreversible transformations
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#
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# Some transformations are destructive in a manner that cannot be reversed. Migrations of that kind should raise
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# an <tt>IrreversibleMigration</tt> exception in their +down+ method.
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#
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# == Running migrations from within Rails
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#
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# The Rails package has several tools to help create and apply migrations.
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#
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# To generate a new migration, use <tt>script/generate migration MyNewMigration</tt>
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# where MyNewMigration is the name of your migration. The generator will
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# create a file <tt>nnn_my_new_migration.rb</tt> in the <tt>db/migrate/</tt>
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# directory, where <tt>nnn</tt> is the next largest migration number.
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# You may then edit the <tt>self.up</tt> and <tt>self.down</tt> methods of
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# n MyNewMigration.
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#
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# To run migrations against the currently configured database, use
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# <tt>rake migrate</tt>. This will update the database by running all of the
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# pending migrations, creating the <tt>schema_info</tt> table if missing.
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#
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# To roll the database back to a previous migration version, use
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# <tt>rake migrate VERSION=X</tt> where <tt>X</tt> is the version to which
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# you wish to downgrade. If any of the migrations throw an
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# <tt>IrreversibleMigration</tt> exception, that step will fail and you'll
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# have some manual work to do.
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#
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# == Database support
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#
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# Migrations are currently supported in MySQL, PostgreSQL, SQLite,
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# SQL Server, Sybase, and Oracle (all supported databases except DB2).
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#
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# == More examples
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#
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# Not all migrations change the schema. Some just fix the data:
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#
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# class RemoveEmptyTags < ActiveRecord::Migration
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# def self.up
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# Tag.find(:all).each { |tag| tag.destroy if tag.pages.empty? }
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# end
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#
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# def self.down
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# # not much we can do to restore deleted data
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# raise IrreversibleMigration
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# end
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# end
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#
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# Others remove columns when they migrate up instead of down:
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#
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# class RemoveUnnecessaryItemAttributes < ActiveRecord::Migration
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# def self.up
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# remove_column :items, :incomplete_items_count
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# remove_column :items, :completed_items_count
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# end
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#
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# def self.down
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# add_column :items, :incomplete_items_count
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# add_column :items, :completed_items_count
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# end
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# end
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#
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# And sometimes you need to do something in SQL not abstracted directly by migrations:
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#
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# class MakeJoinUnique < ActiveRecord::Migration
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# def self.up
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# execute "ALTER TABLE `pages_linked_pages` ADD UNIQUE `page_id_linked_page_id` (`page_id`,`linked_page_id`)"
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# end
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#
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# def self.down
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# execute "ALTER TABLE `pages_linked_pages` DROP INDEX `page_id_linked_page_id`"
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# end
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# end
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#
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# == Using a model after changing its table
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#
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# Sometimes you'll want to add a column in a migration and populate it immediately after. In that case, you'll need
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# to make a call to Base#reset_column_information in order to ensure that the model has the latest column data from
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# after the new column was added. Example:
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#
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# class AddPeopleSalary < ActiveRecord::Migration
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# def self.up
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# add_column :people, :salary, :integer
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# Person.reset_column_information
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# Person.find(:all).each do |p|
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# p.update_attribute :salary, SalaryCalculator.compute(p)
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# end
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# end
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# end
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#
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# == Controlling verbosity
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#
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# By default, migrations will describe the actions they are taking, writing
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# them to the console as they happen, along with benchmarks describing how
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# long each step took.
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#
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# You can quiet them down by setting ActiveRecord::Migration.verbose = false.
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#
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# You can also insert your own messages and benchmarks by using the #say_with_time
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# method:
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#
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# def self.up
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# ...
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# say_with_time "Updating salaries..." do
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# Person.find(:all).each do |p|
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# p.update_attribute :salary, SalaryCalculator.compute(p)
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# end
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# end
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# ...
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# end
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#
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# The phrase "Updating salaries..." would then be printed, along with the
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# benchmark for the block when the block completes.
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class Migration
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@@verbose = true
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cattr_accessor :verbose
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class << self
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def up_using_benchmarks #:nodoc:
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migrate(:up)
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end
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def down_using_benchmarks #:nodoc:
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migrate(:down)
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end
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# Execute this migration in the named direction
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def migrate(direction)
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return unless respond_to?(direction)
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case direction
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when :up then announce "migrating"
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when :down then announce "reverting"
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end
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result = nil
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time = Benchmark.measure { result = send("real_#{direction}") }
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case direction
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when :up then announce "migrated (%.4fs)" % time.real; write
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when :down then announce "reverted (%.4fs)" % time.real; write
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end
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result
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end
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# Because the method added may do an alias_method, it can be invoked
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# recursively. We use @ignore_new_methods as a guard to indicate whether
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# it is safe for the call to proceed.
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def singleton_method_added(sym) #:nodoc:
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return if @ignore_new_methods
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begin
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@ignore_new_methods = true
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case sym
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when :up, :down
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klass = (class << self; self; end)
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klass.send(:alias_method, "real_#{sym}", sym)
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klass.send(:alias_method, sym, "#{sym}_using_benchmarks")
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end
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ensure
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@ignore_new_methods = false
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end
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end
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def write(text="")
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puts(text) if verbose
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end
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def announce(message)
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text = "#{name}: #{message}"
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length = [0, 75 - text.length].max
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write "== %s %s" % [text, "=" * length]
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end
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def say(message, subitem=false)
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write "#{subitem ? " ->" : "--"} #{message}"
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end
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def say_with_time(message)
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say(message)
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result = nil
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time = Benchmark.measure { result = yield }
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say "%.4fs" % time.real, :subitem
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result
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end
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def suppress_messages
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save = verbose
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self.verbose = false
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yield
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ensure
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self.verbose = save
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end
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def method_missing(method, *arguments, &block)
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say_with_time "#{method}(#{arguments.map { |a| a.inspect }.join(", ")})" do
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arguments[0] = Migrator.proper_table_name(arguments.first) unless arguments.empty? || method == :execute
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ActiveRecord::Base.connection.send(method, *arguments, &block)
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end
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end
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end
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end
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class Migrator#:nodoc:
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class << self
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def migrate(migrations_path, target_version = nil)
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Base.connection.initialize_schema_information
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case
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when target_version.nil?, current_version < target_version
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up(migrations_path, target_version)
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when current_version > target_version
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down(migrations_path, target_version)
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when current_version == target_version
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return # You're on the right version
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end
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end
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def up(migrations_path, target_version = nil)
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self.new(:up, migrations_path, target_version).migrate
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end
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def down(migrations_path, target_version = nil)
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self.new(:down, migrations_path, target_version).migrate
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end
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def schema_info_table_name
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Base.table_name_prefix + "schema_info" + Base.table_name_suffix
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end
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def current_version
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(Base.connection.select_one("SELECT version FROM #{schema_info_table_name}") || {"version" => 0})["version"].to_i
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end
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def proper_table_name(name)
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# Use the ActiveRecord objects own table_name, or pre/suffix from ActiveRecord::Base if name is a symbol/string
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name.table_name rescue "#{ActiveRecord::Base.table_name_prefix}#{name}#{ActiveRecord::Base.table_name_suffix}"
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end
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end
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def initialize(direction, migrations_path, target_version = nil)
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raise StandardError.new("This database does not yet support migrations") unless Base.connection.supports_migrations?
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@direction, @migrations_path, @target_version = direction, migrations_path, target_version
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Base.connection.initialize_schema_information
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end
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def current_version
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self.class.current_version
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end
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def migrate
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migration_classes.each do |(version, migration_class)|
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Base.logger.info("Reached target version: #{@target_version}") and break if reached_target_version?(version)
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next if irrelevant_migration?(version)
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Base.logger.info "Migrating to #{migration_class} (#{version})"
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migration_class.migrate(@direction)
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set_schema_version(version)
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end
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end
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private
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def migration_classes
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migrations = migration_files.inject([]) do |migrations, migration_file|
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load(migration_file)
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version, name = migration_version_and_name(migration_file)
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assert_unique_migration_version(migrations, version.to_i)
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migrations << [ version.to_i, migration_class(name) ]
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end
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down? ? migrations.sort.reverse : migrations.sort
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end
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def assert_unique_migration_version(migrations, version)
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if !migrations.empty? && migrations.transpose.first.include?(version)
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raise DuplicateMigrationVersionError.new(version)
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end
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end
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def migration_files
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files = Dir["#{@migrations_path}/[0-9]*_*.rb"].sort_by do |f|
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migration_version_and_name(f).first.to_i
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end
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down? ? files.reverse : files
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end
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def migration_class(migration_name)
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migration_name.camelize.constantize
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end
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def migration_version_and_name(migration_file)
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return *migration_file.scan(/([0-9]+)_([_a-z0-9]*).rb/).first
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end
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def set_schema_version(version)
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Base.connection.update("UPDATE #{self.class.schema_info_table_name} SET version = #{down? ? version.to_i - 1 : version.to_i}")
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end
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def up?
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@direction == :up
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end
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def down?
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@direction == :down
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end
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def reached_target_version?(version)
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return false if @target_version == nil
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(up? && version.to_i - 1 >= @target_version) || (down? && version.to_i <= @target_version)
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end
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def irrelevant_migration?(version)
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(up? && version.to_i <= current_version) || (down? && version.to_i > current_version)
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end
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end
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end
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