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_ADVISORY_LOCK_ID

Lock ID to use for advisory locks when running migrations “sequel-migration”.codepoints.reduce(:*) % (2**63)

MIGRATION_FILE_PATTERN
MUTEX

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) click to toggle source

Wrapper for run, maintaining backwards API compatibility

    # 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
check_current(*args) click to toggle source

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

    # 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) click to toggle source

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
402 def self.is_current?(db, directory, opts=OPTS)
403   migrator_class(directory).new(db, directory, opts).is_current?
404 end
migrator_class(directory) click to toggle source

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
442 def self.migrator_class(directory)
443   if self.equal?(Migrator)
444     raise(Error, "Must supply a valid migration path") unless File.directory?(directory)
445     Dir.new(directory).each 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) click to toggle source

Setup the state for the migrator

    # File lib/sequel/extensions/migration.rb
481 def initialize(db, directory, opts=OPTS)
482   raise(Error, "Must supply a valid migration path") unless File.directory?(directory)
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 ? Sequel::SQL::QualifiedIdentifier.new(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) click to toggle source

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)
    # File lib/sequel/extensions/migration.rb
432 def self.run(db, 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

Private Instance Methods

checked_transaction(migration, &block) click to toggle source

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
498 def checked_transaction(migration, &block)
499   use_trans = if @use_transactions.nil?
500     if migration.use_transactions.nil?
501       @db.supports_transactional_ddl?
502     else
503       migration.use_transactions
504     end
505   else
506     @use_transactions
507   end
508 
509   db.transaction(:skip_transaction=>use_trans == false, &block)
510 end
load_migration_file(file) click to toggle source

Load the migration file, raising an exception if the file does not define a single migration.

    # File lib/sequel/extensions/migration.rb
514 def load_migration_file(file)
515   MUTEX.synchronize do
516     n = Migration.descendants.length
517     load(file)
518     raise Error, "Migration file #{file.inspect} not containing a single migration detected" unless n + 1 == Migration.descendants.length
519     c = Migration.descendants.pop
520     if c.is_a?(Class) && !c.name.to_s.empty? && Object.const_defined?(c.name)
521       Object.send(:remove_const, c.name)
522     end
523     c
524   end
525 end
migration_version_from_file(filename) click to toggle source

Return the integer migration version based on the filename.

    # File lib/sequel/extensions/migration.rb
528 def migration_version_from_file(filename)
529   filename.split('_', 2).first.to_i
530 end