Added migration code based on work by Florian Asmann. Reintroduced me…

…taid dependency. No need to keep a local copy of it.

CHANGELOG

@@ -1,3 +1,9 @@
+=== SVN
+
+* Added migration code based on work by Florian Aßmann.
+
+* Reintroduced metaid dependency. No need to keep a local copy of it.
+
 === 0.1.9.2 (2007-07-24)
 
 * Removed metaid dependency. Refactored requires in lib/sequel.rb.

Rakefile

@@ -43,7 +43,9 @@ spec = Gem::Specification.new do |s|
   s.homepage = 'http://sequel.rubyforge.org'
   s.executables = ['sequel']
 
-  s.required_ruby_version = '>= 1.8.2'
+  s.add_dependency('metaid')
+
+  s.required_ruby_version = '>= 1.8.4'
 
   s.files = %w(COPYING README Rakefile) + Dir.glob("{bin,doc,spec,lib}/**/*")
 

lib/sequel.rb

@@ -1,6 +1,8 @@
+require 'metaid'
+
 files = %w[
-  metaid core_ext error database connection_pool
-  schema pretty_table expressions dataset model
+  core_ext error database connection_pool
+  schema pretty_table expressions dataset migration model
 ]
 dir = File.join(File.dirname(__FILE__), 'sequel')
 files.each {|f| require(File.join(dir, f))}

lib/sequel/migration.rb

@@ -0,0 +1,180 @@
+# The migration code is based on work by Florian Aßmann:
+#   http://code.google.com/p/ruby-sequel/issues/detail?id=23
+
+module Sequel
+  # The Migration class describes a database migration that can be reversed.
+  # The migration looks very similar to ActiveRecord (Rails) migrations, e.g.:
+  #
+  #   class CreateSessions < Sequel::Migration
+  #     def up
+  #       create_table :sessions do
+  #         primary_key :id
+  #         varchar   :session_id, :length => 32, :unique => true
+  #         timestamp :created_at
+  #         text      :data
+  #       end
+  #     end
+  # 
+  #     def down
+  #       execute 'DROP TABLE sessions'
+  #     end
+  #   end
+  #
+  # To apply a migration to a database, you can invoke the #apply with
+  # the target database instance and the direction :up or :down, e.g.:
+  #
+  #   DB = Sequel.open ('sqlite:///mydb')
+  #   CreateSessions.apply(DB, :up)
+  #
+  class Migration
+    # Creates a new instance of the migration and sets the @db attribute.
+    def initialize(db)
+      @db = db
+    end
+
+    # Adds the new migration class to the list of Migration descendants.
+    def self.inherited(base)
+      descendants << base
+    end
+
+    # Returns the list of Migration descendants.
+    def self.descendants
+      @descendants ||= []
+    end
+
+    def up; end #:nodoc:
+    def down; end #:nodoc:
+
+    # Applies the migration to the supplied database in the specified
+    # direction.
+    def self.apply(db, direction)
+      obj = new(db)
+      case direction
+      when :up: obj.up
+      when :down: obj.down
+      else
+        raise SequelError, "Invalid migration direction (#{direction})"
+      end
+    end
+
+    # Intercepts method calls intended for the database and sends them along.
+    def method_missing(method_sym, *args, &block)
+      @db.send method_sym, *args, &block
+    end
+  end
+
+  # 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.
+  #
+  # 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 migration_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)
+  #
+  module Migrator
+    # 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 migration_info table. The migration_info
+    # table is automatically created and maintained by the apply function.
+    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 SequelError, "No current version available" if current.nil?
+      raise SequelError, "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
+    end
+
+    # Returns a list of migration classes filter for the migration range and
+    # ordered according to the migration direction.
+    def self.migration_classes(directory, target, current, direction)
+      range = direction == :up ?
+        (current + 1)..target : (target + 1)..current
+
+      # load migration files
+      Migration.descendants.clear # remove any defined migration classes
+      migration_files(directory, range).each {|fn| load(fn)}
+
+      # get migration classes
+      classes = Migration.descendants
+      classes.reverse! if direction == :down
+      classes
+    end
+
+    MIGRATION_FILE_PATTERN = '[0-9][0-9][0-9]_*.rb'.freeze
+
+    # Returns any found migration files in the supplied directory.
+    def self.migration_files(directory, range = nil)
+      pattern = File.join(directory, MIGRATION_FILE_PATTERN)
+      files = Dir[pattern].inject([]) do |m, path|
+        m[File.basename(path).to_i] = path
+        m
+      end
+      filtered = range ? files[range] : files
+      filtered ? filtered.compact : []
+    end
+
+    def self.latest_migration_version(directory)
+      l = migration_files(directory).last
+      l ? File.basename(l).to_i : nil
+    end
+
+    # Gets the current migration version stored in the database. If no version
+    # number is stored, 0 is returned.
+    def self.get_current_migration_version(db)
+      r = migration_info_dataset(db).first
+      r ? r[:version] : 0
+    end
+
+    # Sets the current migration  version stored in the database.
+    def self.set_current_migration_version(db, version)
+      dataset = migration_info_dataset(db)
+      if dataset.first
+        dataset.update(:version => version)
+      else
+        dataset << {:version => version}
+      end
+    end
+
+    # Returns the dataset for the migration_info table. If no such table
+    # exists, it is automatically created.
+    def self.migration_info_dataset(db)
+      unless db.table_exists?(:migration_info)
+        db.create_table(:migration_info) {integer :version}
+      end
+
+      db[:migration_info]
+    end
+  end
+end