class Sequel::Migrator

  1. lib/sequel/extensions/migration.rb
Superclass: Object

The Migrator class performs migrations based on migration files in a specified directory. The migration files should be named using the following pattern:


For example, the following files are considered migration files:


You can also use timestamps as version numbers:


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:, '.')

For example, to migrate the database all the way down:, '.', target: 0)

For example, to migrate the database to version 4:, '.', target: 4)

To migrate the database from version 1 to version 5:, '.', target: 5, current: 1)

Part of the migration extension.


MIGRATION_FILE_PATTERN = /\A(\d+)_.+\.rb\z/i.freeze  

Mutex used around migration file loading


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
390 def self.apply(db, directory, target = nil, current = nil)
391   run(db, directory, :target => target, :current => current)
392 end

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

[show source]
    # File lib/sequel/extensions/migration.rb
396 def self.check_current(*args)
397   raise(NotCurrentError, 'current migration version does not match latest available version') unless is_current?(*args)
398 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
402 def self.is_current?(db, directory, opts=OPTS)
403   migrator_class(directory).new(db, directory, opts).is_current?
404 end

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
442 def self.migrator_class(directory)
443   if self.equal?(Migrator)
444     raise(Error, "Must supply a valid migration path") unless
445 do |file|
446       next unless MIGRATION_FILE_PATTERN.match(file)
447       return TimestampMigrator if file.split('_', 2).first.to_i > 20000101
448     end
449     IntegerMigrator
450   else
451     self
452   end
453 end
new(db, directory, opts=OPTS)

Setup the state for the migrator

[show source]
    # File lib/sequel/extensions/migration.rb
481 def initialize(db, directory, opts=OPTS)
482   raise(Error, "Must supply a valid migration path") unless
483   @db = db
484   @directory = directory
485   @allow_missing_migration_files = opts[:allow_missing_migration_files]
486   @files = get_migration_files
487   schema, table = @db.send(:schema_and_table, opts[:table] || default_schema_table)
488   @table = schema ?, table) : table
489   @column = opts[:column] || default_schema_column
490   @ds = schema_dataset
491   @use_transactions = opts[:use_transactions]
492 end
run(db, directory, opts=OPTS)

Migrates the supplied database using the migration files in the specified directory. Options:


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.


The column in the :table argument storing the migration version (default: :version).


The current version of the database. If not given, it is retrieved from the database using the :table and :column options.


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).


The table containing the schema version (default: :schema_info for integer migrations and :schema_migrations for timestamped migrations).


The target version to which to migrate. If not given, migrates to the maximum version.


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

Examples:, "migrations"), "migrations", target: 15, current: 10), "app1/migrations", column: :app2_version), "app2/migrations", column: :app2_version, table: :schema_info2)
[show source]
    # File lib/sequel/extensions/migration.rb
432 def, directory, opts=OPTS)
433   if opts[:use_advisory_lock]
434     db.with_advisory_lock(MIGRATION_ADVISORY_LOCK_ID){run(db, directory, opts.merge(:use_advisory_lock=>false))}
435   else
436     migrator_class(directory).new(db, directory, opts).run
437   end
438 end