rails--rails/activerecord/lib/active_record/schema.rb

module ActiveRecord
  # Allows programmers to programmatically define a schema in a portable
  # DSL. This means you can define tables, indexes, etc. without using SQL
  # directly, so your applications can more easily support multiple
  # databases.
  #
  # Usage:
  #
  #   ActiveRecord::Schema.define do
  #     create_table :authors do |t|
  #       t.column :name, :string, :null => false
  #     end
  #
  #     add_index :authors, :name, :unique
  #
  #     create_table :posts do |t|
  #       t.column :author_id, :integer, :null => false
  #       t.column :subject, :string
  #       t.column :body, :text
  #       t.column :private, :boolean, :default => false
  #     end
  #
  #     add_index :posts, :author_id
  #   end
  #
  # ActiveRecord::Schema is only supported by database adapters that also
  # support migrations, the two features being very similar.
  class Schema < Migration
    private_class_method :new

    # Eval the given block. All methods available to the current connection
    # adapter are available within the block, so you can easily use the
    # database definition DSL to build up your schema (#create_table,
    # #add_index, etc.).
    #
    # The +info+ hash is optional, and if given is used to define metadata
    # about the current schema (like the schema's version):
    #
    #   ActiveRecord::Schema.define(:version => 15) do
    #     ...
    #   end
    def self.define(info={}, &block)
      instance_eval(&block)

      unless info.empty?
        initialize_schema_information
        cols = columns('schema_info')

        info = info.map do |k,v|
          v = quote(v, cols.detect { |c| c.name == k.to_s })
          "#{k} = #{v}"
        end

        update "UPDATE schema_info SET #{info.join(", ")}"
      end
    end
  end
end