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

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
371 def self.apply(db, directory, target = nil, current = nil)
372   run(db, directory, :target => target, :current => current)
373 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
377 def self.check_current(*args)
378   raise(NotCurrentError, 'migrator is not current') unless is_current?(*args)
379 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
383 def self.is_current?(db, directory, opts=OPTS)
384   migrator_class(directory).new(db, directory, opts).is_current?
385 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
409 def self.migrator_class(directory)
410   if self.equal?(Migrator)
411     raise(Error, "Must supply a valid migration path") unless File.directory?(directory)
412     Dir.new(directory).each do |file|
413       next unless MIGRATION_FILE_PATTERN.match(file)
414       return TimestampMigrator if file.split('_', 2).first.to_i > 20000101
415     end
416     IntegerMigrator
417   else
418     self
419   end
420 end
new(db, directory, opts=OPTS) click to toggle source

Setup the state for the migrator

    # File lib/sequel/extensions/migration.rb
448 def initialize(db, directory, opts=OPTS)
449   raise(Error, "Must supply a valid migration path") unless File.directory?(directory)
450   @db = db
451   @directory = directory
452   @allow_missing_migration_files = opts[:allow_missing_migration_files]
453   @files = get_migration_files
454   schema, table = @db.send(:schema_and_table, opts[:table] || default_schema_table)
455   @table = schema ? Sequel::SQL::QualifiedIdentifier.new(schema, table) : table
456   @column = opts[:column] || default_schema_column
457   @ds = schema_dataset
458   @use_transactions = opts[:use_transactions]
459 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.

: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
403 def self.run(db, directory, opts=OPTS)
404   migrator_class(directory).new(db, directory, opts).run
405 end

Private Instance Methods

checked_transaction(migration) { || ... } 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
465 def checked_transaction(migration, &block)
466   use_trans = if @use_transactions.nil?
467     if migration.use_transactions.nil?
468       @db.supports_transactional_ddl?
469     else
470       migration.use_transactions
471     end
472   else
473     @use_transactions
474   end
475 
476   if use_trans
477     db.transaction(&block)
478   else
479     yield
480   end
481 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
485 def load_migration_file(file)
486   MUTEX.synchronize do
487     n = Migration.descendants.length
488     load(file)
489     raise Error, "Migration file #{file.inspect} not containing a single migration detected" unless n + 1 == Migration.descendants.length
490     c = Migration.descendants.pop
491     if c.is_a?(Class) && !c.name.to_s.empty? && Object.const_defined?(c.name)
492       Object.send(:remove_const, c.name)
493     end
494     c
495   end
496 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
499 def migration_version_from_file(filename)
500   filename.split('_', 2).first.to_i
501 end