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.
Methods
Public Class
Public Instance
Classes and Modules
Constants
| MIGRATION_FILE_PATTERN | = | /\A(\d+)_.+\.rb\z/i.freeze | ||
| MUTEX | = | Mutex.new |
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 |
| 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
Wrapper for run, maintaining backwards API compatibility
# File lib/sequel/extensions/migration.rb 373 def self.apply(db, directory, target = nil, current = nil) 374 run(db, directory, :target => target, :current => current) 375 end
Raise a NotCurrentError unless the migrator is current, takes the same arguments as run.
# File lib/sequel/extensions/migration.rb 379 def self.check_current(*args) 380 raise(NotCurrentError, 'migrator is not current') unless is_current?(*args) 381 end
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 385 def self.is_current?(db, directory, opts=OPTS) 386 migrator_class(directory).new(db, directory, opts).is_current? 387 end
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 414 def self.migrator_class(directory) 415 if self.equal?(Migrator) 416 raise(Error, "Must supply a valid migration path") unless File.directory?(directory) 417 Dir.new(directory).each do |file| 418 next unless MIGRATION_FILE_PATTERN.match(file) 419 return TimestampMigrator if file.split('_', 2).first.to_i > 20000101 420 end 421 IntegerMigrator 422 else 423 self 424 end 425 end
Setup the state for the migrator
# File lib/sequel/extensions/migration.rb 453 def initialize(db, directory, opts=OPTS) 454 raise(Error, "Must supply a valid migration path") unless File.directory?(directory) 455 @db = db 456 @directory = directory 457 @allow_missing_migration_files = opts[:allow_missing_migration_files] 458 @files = get_migration_files 459 schema, table = @db.send(:schema_and_table, opts[:table] || default_schema_table) 460 @table = schema ? Sequel::SQL::QualifiedIdentifier.new(schema, table) : table 461 @column = opts[:column] || default_schema_column 462 @ds = schema_dataset 463 @use_transactions = opts[:use_transactions] 464 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 ( |
| :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 408 def self.run(db, directory, opts=OPTS) 409 migrator_class(directory).new(db, directory, opts).run 410 end