schema_dumper.rb

require 'stringio'
require 'active_support/core_ext/big_decimal'

module ActiveRecord
  # This class is used to dump the database schema for some connection to some
  # output format (i.e., ActiveRecord::Schema).
  class SchemaDumper #:nodoc:
    private_class_method :new
    
    ##
    # :singleton-method:
    # A list of tables which should not be dumped to the schema. 
    # Acceptable values are strings as well as regexp.
    # This setting is only used if ActiveRecord::Base.schema_format == :ruby
    cattr_accessor :ignore_tables 
    @@ignore_tables = []

    def self.dump(connection=ActiveRecord::Base.connection, stream=STDOUT)
      new(connection).dump(stream)
      stream
    end

    def dump(stream)
      header(stream)
      tables(stream)
      trailer(stream)
      stream
    end

    private

      def initialize(connection)
        @connection = connection
        @types = @connection.native_database_types
        @version = Migrator::current_version rescue nil
      end

      def header(stream)
        define_params = @version ? ":version => #{@version}" : ""

        stream.puts <<HEADER
# This file is auto-generated from the current state of the database. Instead of editing this file, 
# please use the migrations feature of Active Record to incrementally modify your database, and
# then regenerate this schema definition.
#
# Note that this schema.rb definition is the authoritative source for your database schema. If you need
# to create the application database on another system, you should be using db:schema:load, not running
# all the migrations from scratch. The latter is a flawed and unsustainable approach (the more migrations
# you'll amass, the slower it'll run and the greater likelihood for issues).
#
# It's strongly recommended to check this file into your version control system.

ActiveRecord::Schema.define(#{define_params}) do

HEADER
      end

      def trailer(stream)
        stream.puts "end"
      end

      def tables(stream)
        @connection.tables.sort.each do |tbl|
          next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|
            case ignored
            when String; tbl == ignored
            when Regexp; tbl =~ ignored
            else
              raise StandardError, 'ActiveRecord::SchemaDumper.ignore_tables accepts an array of String and / or Regexp values.'
            end
          end 
          table(tbl, stream)
        end
      end

      def table(table, stream)
        columns = @connection.columns(table)
        begin
          tbl = StringIO.new

          # first dump primary key column
          if @connection.respond_to?(:pk_and_sequence_for)
            pk, pk_seq = @connection.pk_and_sequence_for(table)
          elsif @connection.respond_to?(:primary_key)
            pk = @connection.primary_key(table)
          end
          
          tbl.print "  create_table #{table.inspect}"
          if columns.detect { |c| c.name == pk }
            if pk != 'id'
              tbl.print %Q(, :primary_key => "#{pk}")
            end
          else
            tbl.print ", :id => false"
          end
          tbl.print ", :force => true"
          tbl.puts " do |t|"

          # then dump all non-primary key columns
          column_specs = columns.map do |column|
            raise StandardError, "Unknown type '#{column.sql_type}' for column '#{column.name}'" if @types[column.type].nil?
            next if column.name == pk
            spec = {}
            spec[:name]      = column.name.inspect
            
            # AR has an optimisation which handles zero-scale decimals as integers.  This
            # code ensures that the dumper still dumps the column as a decimal.
            spec[:type]      = if column.type == :integer && [/^numeric/, /^decimal/].any? { |e| e.match(column.sql_type) }
                                 'decimal'
                               else
                                 column.type.to_s
                               end
            spec[:limit]     = column.limit.inspect if column.limit != @types[column.type][:limit] && spec[:type] != 'decimal'
            spec[:precision] = column.precision.inspect if !column.precision.nil?
            spec[:scale]     = column.scale.inspect if !column.scale.nil?
            spec[:null]      = 'false' if !column.null
            spec[:default]   = default_string(column.default) if column.has_default?
            (spec.keys - [:name, :type]).each{ |k| spec[k].insert(0, "#{k.inspect} => ")}
            spec
          end.compact

          # find all migration keys used in this table
          keys = [:name, :limit, :precision, :scale, :default, :null] & column_specs.map(&:keys).flatten

          # figure out the lengths for each column based on above keys
          lengths = keys.map{ |key| column_specs.map{ |spec| spec[key] ? spec[key].length + 2 : 0 }.max }

          # the string we're going to sprintf our values against, with standardized column widths
          format_string = lengths.map{ |len| "%-#{len}s" }

          # find the max length for the 'type' column, which is special
          type_length = column_specs.map{ |column| column[:type].length }.max

          # add column type definition to our format string
          format_string.unshift "    t.%-#{type_length}s "

          format_string *= ''

          column_specs.each do |colspec|
            values = keys.zip(lengths).map{ |key, len| colspec.key?(key) ? colspec[key] + ", " : " " * len }
            values.unshift colspec[:type]
            tbl.print((format_string % values).gsub(/,\s*$/, ''))
            tbl.puts
          end

          tbl.puts "  end"
          tbl.puts
          
          indexes(table, tbl)

          tbl.rewind
          stream.print tbl.read
        rescue => e
          stream.puts "# Could not dump table #{table.inspect} because of following #{e.class}"
          stream.puts "#   #{e.message}"
          stream.puts
        end
        
        stream
      end

      def default_string(value)
        case value
        when BigDecimal
          value.to_s
        when Date, DateTime, Time
          "'" + value.to_s(:db) + "'"
        else
          value.inspect
        end
      end
      
      def indexes(table, stream)
        if (indexes = @connection.indexes(table)).any?
          add_index_statements = indexes.map do |index|
            statment_parts = [ ('add_index ' + index.table.inspect) ]
            statment_parts << index.columns.inspect
            statment_parts << (':name => ' + index.name.inspect)
            statment_parts << ':unique => true' if index.unique

            index_lengths = index.lengths.compact if index.lengths.is_a?(Array)
            statment_parts << (':length => ' + Hash[*index.columns.zip(index.lengths).flatten].inspect) if index_lengths.present?

            '  ' + statment_parts.join(', ')
          end

          stream.puts add_index_statements.sort.join("\n")
          stream.puts
        end
      end
  end
end