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
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.

[show source]
    # 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
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
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.

[show source]
    # 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
421 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
new(db, directory, opts=OPTS)

Setup the state for the migrator

[show source]
    # File lib/sequel/extensions/migration.rb
457 def initialize(db, directory, opts=OPTS)
458   raise(Error, "Must supply a valid migration path") unless
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 ?, table) : table
465   @column = opts[:column] || default_schema_column
466   @ds = schema_dataset
467   @use_transactions = opts[:use_transactions]
468 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.

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
412 def, directory, opts=OPTS)
413   migrator_class(directory).new(db, directory, opts).run
414 end