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 390 def self.apply(db, directory, target = nil, current = nil) 391 run(db, directory, :target => target, :current => current) 392 end
Wrapper for run
, maintaining backwards API compatibility
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
Raise a NotCurrentError
unless the migrator is current, takes the same arguments as run.
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
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 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
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 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
Setup the state for the migrator
Source
# 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
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 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
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 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
Load the migration file, raising an exception if the file does not define a single migration.
Source
# File lib/sequel/extensions/migration.rb 528 def migration_version_from_file(filename) 529 filename.split('_', 2).first.to_i 530 end
Return the integer migration version based on the filename.