Module: Sequel::Migrator

Defined in:
lib/sequel_core/migration.rb

Overview

The Migrator module performs migrations based on migration files in a specified directory. The migration files should be named using the following pattern (in similar fashion to ActiveRecord migrations):

<version>_<title>.rb

For example, the following files are considered migration files:

001_create_sessions.rb
002_add_data_column.rb
...

The migration files should contain one or more migration classes based on Sequel::Migration.

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 migration, 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 schema_info table 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, 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.apply(DB, '.')

To migrate the database from version 1 to version 5:

Sequel::Migrator.apply(DB, '.', 5, 1)

Constant Summary collapse

MIGRATION_FILE_PATTERN = 
/\A\d+_.+\.rb\z/.freeze

Class Method Summary collapse

Class Method Details

.apply(db, directory, target = nil, current = nil) ⇒ Object

Migrates the supplied database in the specified directory from the current version to the target version. If no current version is supplied, it is extracted from a schema_info table. The schema_info table is automatically created and maintained by the apply function.

Raises:



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# File 'lib/sequel_core/migration.rb', line 118

def self.apply(db, directory, target = nil, current = nil)
  # determine current and target version and direction
  current ||= get_current_migration_version(db)
  target ||= latest_migration_version(directory)
  raise Error, "No current version available" if current.nil?
  raise Error, "No target version available" if target.nil?

  direction = current < target ? :up : :down
  
  classes = migration_classes(directory, target, current, direction)
  
  db.transaction do
    classes.each {|c| c.apply(db, direction)}
    set_current_migration_version(db, target)
  end
  
  target
end

.get_current_migration_version(db) ⇒ Object

Gets the current migration version stored in the database. If no version number is stored, 0 is returned.



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# File 'lib/sequel_core/migration.rb', line 139

def self.get_current_migration_version(db)
  r = schema_info_dataset(db).first
  r ? r[:version] : 0
end

.latest_migration_version(directory) ⇒ Object

Returns the latest version available in the specified directory.



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# File 'lib/sequel_core/migration.rb', line 145

def self.latest_migration_version(directory)
  l = migration_files(directory).last
  l ? File.basename(l).to_i : nil
end

.migration_classes(directory, target, current, direction) ⇒ Object

Returns a list of migration classes filtered for the migration range and ordered according to the migration direction.



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# File 'lib/sequel_core/migration.rb', line 152

def self.migration_classes(directory, target, current, direction)
  range = direction == :up ?
    (current + 1)..target : (target + 1)..current

  # Remove class definitions
  Migration.descendants.each do |c|
    Object.send(:remove_const, c.to_s) rescue nil
  end
  Migration.descendants.clear # remove any defined migration classes

  # load migration files
  migration_files(directory, range).each {|fn| load(fn)}
  
  # get migration classes
  classes = Migration.descendants
  classes.reverse! if direction == :down
  classes
end

.migration_files(directory, range = nil) ⇒ Object

Returns any found migration files in the supplied directory.



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# File 'lib/sequel_core/migration.rb', line 172

def self.migration_files(directory, range = nil)
  files = []
  Dir.new(directory).each do |file|
    files[file.to_i] = File.join(directory, file) if MIGRATION_FILE_PATTERN.match(file)
  end
  filtered = range ? files[range] : files
  filtered ? filtered.compact : []
end

.schema_info_dataset(db) ⇒ Object

Returns the dataset for the schema_info table. If no such table exists, it is automatically created.



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# File 'lib/sequel_core/migration.rb', line 183

def self.schema_info_dataset(db)
  db.create_table(:schema_info) {integer :version} unless db.table_exists?(:schema_info)
  db[:schema_info]
end

.set_current_migration_version(db, version) ⇒ Object

Sets the current migration version stored in the database.



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# File 'lib/sequel_core/migration.rb', line 189

def self.set_current_migration_version(db, version)
  dataset = schema_info_dataset(db)
  dataset.send(dataset.first ? :update : :<<, :version => version)
end