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.

Methods

Public Instance

column
db
directory
ds
files
table
target

Classes and Modules

Constants

MIGRATION_FILE_PATTERN	=	/\A(\d+)_(.+)\.rb\z/i.freeze
MUTEX	=	Mutex.new		Mutex used around migration file loading

Attributes

column	[R]	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)
db	[R]	The database related to this migrator
directory	[R]	The directory for this migrator’s files
ds	[R]	The dataset for this migrator, representing the `schema_info` table for integer migrations and the `schema_migrations` table for timestamp migrations
files	[R]	All migration files in this migrator’s directory
table	[R]	The table to use to hold the applied migration data (defaults to :schema_info for integer migrations and :schema_migrations for timestamp migrations)
target	[R]	The target version for this migrator

Public Class methods

apply(db, directory, target = nil, current = nil)

Wrapper for run, maintaining backwards API compatibility

[show source]

    # File lib/sequel/extensions/migration.rb
394 def self.apply(db, directory, target = nil, current = nil)
395   run(db, directory, :target => target, :current => current)
396 end

check_current(*args)

Raise a NotCurrentError unless the migrator is current, takes the same arguments as run.

[show source]

    # File lib/sequel/extensions/migration.rb
400 def self.check_current(*args)
401   raise(NotCurrentError, 'current migration version does not match latest available version') unless is_current?(*args)
402 end

is_current?(db, directory, opts=OPTS)

Return whether the migrator is current (i.e. it does not need to make any changes). Takes the same arguments as run.

[show source]

    # File lib/sequel/extensions/migration.rb
406 def self.is_current?(db, directory, opts=OPTS)
407   migrator_class(directory).new(db, directory, opts).is_current?
408 end

migrator_class(directory)

Choose the Migrator subclass to use. Uses the TimestampMigrator if the version number is greater than 20000101, otherwise uses the IntegerMigrator.

[show source]

    # File lib/sequel/extensions/migration.rb
446 def self.migrator_class(directory)
447   if self.equal?(Migrator)
448     raise(Error, "Must supply a valid migration path") unless File.directory?(directory)
449     Dir.new(directory).each do |file|
450       next unless MIGRATION_FILE_PATTERN.match(file)
451       return TimestampMigrator if file.split('_', 2).first.to_i > 20000101
452     end
453     IntegerMigrator
454   else
455     self
456   end
457 end

new(db, directory, opts=OPTS)

Setup the state for the migrator

[show source]

    # File lib/sequel/extensions/migration.rb
485 def initialize(db, directory, opts=OPTS)
486   raise(Error, "Must supply a valid migration path") unless File.directory?(directory)
487   @db = db
488   @directory = directory
489   @allow_missing_migration_files = opts[:allow_missing_migration_files]
490   @files = get_migration_files
491   schema, table = @db.send(:schema_and_table, opts[:table] || default_schema_table)
492   @table = schema ? Sequel::SQL::QualifiedIdentifier.new(schema, table) : table
493   @column = opts[:column] || default_schema_column
494   @ds = schema_dataset
495   @use_transactions = opts[:use_transactions]
496 end

run(db, directory, opts=OPTS)

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.
:use_advisory_lock	Use advisory locks in migrations (only use this if `Sequel` supports advisory locks for the database).

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)

[show source]

    # File lib/sequel/extensions/migration.rb
436 def self.run(db, directory, opts=OPTS)
437   if opts[:use_advisory_lock]
438     db.with_advisory_lock(MIGRATION_ADVISORY_LOCK_ID){run(db, directory, opts.merge(:use_advisory_lock=>false))}
439   else
440     migrator_class(directory).new(db, directory, opts).run
441   end
442 end

class Sequel::Migrator

Methods

Public Class

Public Instance

Classes and Modules

Constants

Attributes

Public Class methods