class Sequel::Migrator
The Migrator
class performs migrations based on migration files in a specified directory. The migration files should be named using the following pattern:
<version>_<title>.rb
For example, the following files are considered migration files:
001_create_sessions.rb 002_add_data_column.rb
You can also use timestamps as version numbers:
1273253850_create_sessions.rb 1273257248_add_data_column.rb
If any migration filenames use timestamps as version numbers, Sequel
uses the TimestampMigrator
to migrate, otherwise it uses the IntegerMigrator
. The TimestampMigrator
can handle migrations that are run out of order as well as migrations with the same timestamp, while the IntegerMigrator
is more strict and raises exceptions for missing or duplicate migration files.
The migration files should contain either one Migration
subclass or one Sequel.migration
call.
Migrations are generally run via the sequel command line tool, using the -m and -M switches. The -m switch specifies the migration directory, and the -M switch specifies the version to which to migrate.
You can apply migrations using the Migrator
API, as well (this is necessary if you want to specify the version from which to migrate in addition to the version to which to migrate). To apply a migrator, the apply
method must be invoked with the database instance, the directory of migration files and the target version. If no current version is supplied, it is read from the database. The migrator automatically creates a table (schema_info for integer migrations and schema_migrations for timestamped migrations). in the database to keep track of the current migration version. If no migration version is stored in the database, the version is considered to be 0. If no target version is specified, or the target version specified is greater than the latest version available, the database is migrated to the latest version available in the migration directory.
For example, to migrate the database to the latest version:
Sequel::Migrator.run(DB, '.')
For example, to migrate the database all the way down:
Sequel::Migrator.run(DB, '.', target: 0)
For example, to migrate the database to version 4:
Sequel::Migrator.run(DB, '.', target: 4)
To migrate the database from version 1 to version 5:
Sequel::Migrator.run(DB, '.', target: 5, current: 1)
Part of the migration
extension.
Constants
- MIGRATION_FILE_PATTERN
- MUTEX
Mutex used around migration file loading
Attributes
The column to use to hold the migration version number for integer migrations or filename for timestamp migrations (defaults to :version for integer migrations and :filename for timestamp migrations)
The database related to this migrator
The directory for this migrator's files
The dataset for this migrator, representing the schema_info
table for integer migrations and the schema_migrations
table for timestamp migrations
All migration files in this migrator's directory
The table to use to hold the applied migration data (defaults to :schema_info for integer migrations and :schema_migrations for timestamp migrations)
The target version for this migrator
Public Class Methods
Wrapper for run
, maintaining backwards API compatibility
# File lib/sequel/extensions/migration.rb 373 def self.apply(db, directory, target = nil, current = nil) 374 run(db, directory, :target => target, :current => current) 375 end
Raise a NotCurrentError
unless the migrator is current, takes the same arguments as run.
# File lib/sequel/extensions/migration.rb 379 def self.check_current(*args) 380 raise(NotCurrentError, 'migrator is not current') unless is_current?(*args) 381 end
Return whether the migrator is current (i.e. it does not need to make any changes). Takes the same arguments as run.
# File lib/sequel/extensions/migration.rb 385 def self.is_current?(db, directory, opts=OPTS) 386 migrator_class(directory).new(db, directory, opts).is_current? 387 end
Choose the Migrator
subclass to use. Uses the TimestampMigrator
if the version number is greater than 20000101, otherwise uses the IntegerMigrator
.
# File lib/sequel/extensions/migration.rb 411 def self.migrator_class(directory) 412 if self.equal?(Migrator) 413 raise(Error, "Must supply a valid migration path") unless File.directory?(directory) 414 Dir.new(directory).each do |file| 415 next unless MIGRATION_FILE_PATTERN.match(file) 416 return TimestampMigrator if file.split('_', 2).first.to_i > 20000101 417 end 418 IntegerMigrator 419 else 420 self 421 end 422 end
Setup the state for the migrator
# File lib/sequel/extensions/migration.rb 450 def initialize(db, directory, opts=OPTS) 451 raise(Error, "Must supply a valid migration path") unless File.directory?(directory) 452 @db = db 453 @directory = directory 454 @allow_missing_migration_files = opts[:allow_missing_migration_files] 455 @files = get_migration_files 456 schema, table = @db.send(:schema_and_table, opts[:table] || default_schema_table) 457 @table = schema ? Sequel::SQL::QualifiedIdentifier.new(schema, table) : table 458 @column = opts[:column] || default_schema_column 459 @ds = schema_dataset 460 @use_transactions = opts[:use_transactions] 461 end
Migrates the supplied database using the migration files in the specified directory. Options:
- :allow_missing_migration_files
-
Don't raise an error if there are missing migration files.
- :column
-
The column in the :table argument storing the migration version (default: :version).
- :current
-
The current version of the database. If not given, it is retrieved from the database using the :table and :column options.
- :relative
-
Run the given number of migrations, with a positive number being migrations to migrate up, and a negative number being migrations to migrate down (
IntegerMigrator
only). - :table
-
The table containing the schema version (default: :schema_info for integer migrations and :schema_migrations for timestamped migrations).
- :target
-
The target version to which to migrate. If not given, migrates to the maximum version.
Examples:
Sequel::Migrator.run(DB, "migrations") Sequel::Migrator.run(DB, "migrations", target: 15, current: 10) Sequel::Migrator.run(DB, "app1/migrations", column: :app2_version) Sequel::Migrator.run(DB, "app2/migrations", column: :app2_version, table: :schema_info2)
# File lib/sequel/extensions/migration.rb 405 def self.run(db, directory, opts=OPTS) 406 migrator_class(directory).new(db, directory, opts).run 407 end
Private Instance Methods
If transactions should be used for the migration, yield to the block inside a transaction. Otherwise, just yield to the block.
# File lib/sequel/extensions/migration.rb 467 def checked_transaction(migration, &block) 468 use_trans = if @use_transactions.nil? 469 if migration.use_transactions.nil? 470 @db.supports_transactional_ddl? 471 else 472 migration.use_transactions 473 end 474 else 475 @use_transactions 476 end 477 478 if use_trans 479 db.transaction(&block) 480 else 481 yield 482 end 483 end
Load the migration file, raising an exception if the file does not define a single migration.
# File lib/sequel/extensions/migration.rb 487 def load_migration_file(file) 488 MUTEX.synchronize do 489 n = Migration.descendants.length 490 load(file) 491 raise Error, "Migration file #{file.inspect} not containing a single migration detected" unless n + 1 == Migration.descendants.length 492 c = Migration.descendants.pop 493 if c.is_a?(Class) && !c.name.to_s.empty? && Object.const_defined?(c.name) 494 Object.send(:remove_const, c.name) 495 end 496 c 497 end 498 end
Return the integer migration version based on the filename.
# File lib/sequel/extensions/migration.rb 501 def migration_version_from_file(filename) 502 filename.split('_', 2).first.to_i 503 end