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
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)
The database related to this migrator
The directory for this migrator’s files
The dataset for this migrator, representing the schema_info
table for integer migrations and the schema_migrations
table for timestamp migrations
All migration files in this migrator’s directory
The table to use to hold the applied migration data (defaults to :schema_info for integer migrations and :schema_migrations for timestamp migrations)
The target version for this migrator
Public Class Methods
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
Wrapper for run
, maintaining backwards API compatibility
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
Raise a NotCurrentError
unless the migrator is current, takes the same arguments as run.
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
Return whether the migrator is current (i.e. it does not need to make any changes). Takes the same arguments as run.
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
Choose the Migrator
subclass to use. Uses the TimestampMigrator
if the version number is greater than 20000101, otherwise uses the IntegerMigrator
.
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
Setup the state for the migrator
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
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)
Private Instance Methods
Source
# File lib/sequel/extensions/migration.rb 502 def checked_transaction(migration, &block) 503 use_trans = if @use_transactions.nil? 504 if migration.use_transactions.nil? 505 @db.supports_transactional_ddl? 506 else 507 migration.use_transactions 508 end 509 else 510 @use_transactions 511 end 512 513 db.transaction(:skip_transaction=>use_trans == false, &block) 514 end
If transactions should be used for the migration, yield to the block inside a transaction. Otherwise, just yield to the block.
Source
# File lib/sequel/extensions/migration.rb 518 def load_migration_file(file) 519 MUTEX.synchronize do 520 n = Migration.descendants.length 521 load(file) 522 raise Error, "Migration file #{file.inspect} not containing a single migration detected" unless n + 1 == Migration.descendants.length 523 c = Migration.descendants.pop 524 if c.is_a?(Class) && !c.name.to_s.empty? && Object.const_defined?(c.name) 525 Object.send(:remove_const, c.name) 526 end 527 c 528 end 529 end
Load the migration file, raising an exception if the file does not define a single migration.
Source
# File lib/sequel/extensions/migration.rb 532 def migration_version_from_file(filename) 533 filename.split('_', 2).first.to_i 534 end
Return the integer migration version based on the filename.