Monkeypatching Rails SchemaDumper to support sequences.

schema_dumper_sequences.rb

class ActiveRecord::SchemaDumper
  def dump(stream)
    header(stream)
    tables(stream)
    sequences(stream)
    sequence_defaults(stream)
    trailer(stream)
    stream
  end

  private

  def sequences(stream)
    sequences = @connection.select_values("SELECT c.relname FROM pg_class c WHERE c.relkind = 'S';")
    sequences.each do |sequence|
      next if sequence.match(/_id_seq$/) # Skip sequences for ids. Rails handles these automatically.

      minval = @connection.select_value("SELECT min_value FROM #{ sequence };")
      stream.puts format('  execute("CREATE SEQUENCE %s MINVALUE %d;")', sequence, minval)
    end
  end

  # Rails doesn't understand functions in defaults, so we have to do this ourselves.
  def sequence_defaults(stream)
    sql =<<-SQL
      SELECT
        table_name, column_name, column_default
      FROM
        information_schema.columns
      WHERE
        column_default LIKE 'nextval(%' AND
        column_name != 'id';
    SQL

    sequence_defaults = @connection.select_rows(sql)
    sequence_defaults.each do |table, column, default|
      stream.puts format('  execute("ALTER TABLE %s ALTER COLUMN %s SET DEFAULT %s;")', table, column, default)
    end
  end
end