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 377 def self.apply(db, directory, target = nil, current = nil) 378 run(db, directory, :target => target, :current => current) 379 end
Raise a NotCurrentError
unless the migrator is current, takes the same arguments as run.
# File lib/sequel/extensions/migration.rb 383 def self.check_current(*args) 384 raise(NotCurrentError, 'current migration version does not match latest available version') unless is_current?(*args) 385 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 389 def self.is_current?(db, directory, opts=OPTS) 390 migrator_class(directory).new(db, directory, opts).is_current? 391 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 418 def self.migrator_class(directory) 419 if self.equal?(Migrator) 420 raise(Error, "Must supply a valid migration path") unless File.directory?(directory) 421 Dir.new(directory).each do |file| 422 next unless MIGRATION_FILE_PATTERN.match(file) 423 return TimestampMigrator if file.split('_', 2).first.to_i > 20000101 424 end 425 IntegerMigrator 426 else 427 self 428 end 429 end
Setup the state for the migrator
# File lib/sequel/extensions/migration.rb 457 def initialize(db, directory, opts=OPTS) 458 raise(Error, "Must supply a valid migration path") unless File.directory?(directory) 459 @db = db 460 @directory = directory 461 @allow_missing_migration_files = opts[:allow_missing_migration_files] 462 @files = get_migration_files 463 schema, table = @db.send(:schema_and_table, opts[:table] || default_schema_table) 464 @table = schema ? Sequel::SQL::QualifiedIdentifier.new(schema, table) : table 465 @column = opts[:column] || default_schema_column 466 @ds = schema_dataset 467 @use_transactions = opts[:use_transactions] 468 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. It is very risky to use this option, since it can result in the database schema version number not matching the expected database schema.
- :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 412 def self.run(db, directory, opts=OPTS) 413 migrator_class(directory).new(db, directory, opts).run 414 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 474 def checked_transaction(migration, &block) 475 use_trans = if @use_transactions.nil? 476 if migration.use_transactions.nil? 477 @db.supports_transactional_ddl? 478 else 479 migration.use_transactions 480 end 481 else 482 @use_transactions 483 end 484 485 if use_trans 486 db.transaction(&block) 487 else 488 yield 489 end 490 end
Load the migration file, raising an exception if the file does not define a single migration.
# File lib/sequel/extensions/migration.rb 494 def load_migration_file(file) 495 MUTEX.synchronize do 496 n = Migration.descendants.length 497 load(file) 498 raise Error, "Migration file #{file.inspect} not containing a single migration detected" unless n + 1 == Migration.descendants.length 499 c = Migration.descendants.pop 500 if c.is_a?(Class) && !c.name.to_s.empty? && Object.const_defined?(c.name) 501 Object.send(:remove_const, c.name) 502 end 503 c 504 end 505 end
Return the integer migration version based on the filename.
# File lib/sequel/extensions/migration.rb 508 def migration_version_from_file(filename) 509 filename.split('_', 2).first.to_i 510 end