gistfile1.rb

class ActiveRecord::Base

  def self.bulk_import(flush_after=50, &blk)
    @bulk_import_columns     = Set.new
    @bulk_import_rows        = []
    @bulk_import_flush_after = flush_after

    class << self
      # this is essentially alias_method_chain written out for symmetry
      # with the part that undoes it
      alias_method :create_without_bulk_import, :create
      alias_method :create, :create_with_bulk_import
      yield
    ensure
      alias_method :create_with_bulk_import, :create
      alias_method :create, :create_without_bulk_import
    end
    flush_bulk_import
  end

  def self.create_with_bulk_import(attributes=nil)
    @bulk_import_columns += attributes.keys
    @bulk_import_rows    << attributes

    if @bulk_import_rows.length >= @bulk_import_flush_after
      flush_bulk_import
    end
  end

  def self.flush_bulk_import
    return unless @bulk_import_rows.length > 0

    query = %{
      INSERT INTO #{self.table_name}
        (#{@bulk_import_columns.map { |c| connection.quote_column_name(c) }.join(',')})
      VALUES
        #{
          @bulk_import_rows.map do |row|
            "(%s)" % (@bulk_import_columns.map do |column|
              quote_bound_value(row[column])
            end.join(','))
          end.join(',')
        }
    }.squish

    self.connection.execute query
    @bulk_import_rows = []
  end

end

gistfile2.rb

MyObject.bulk_import do
  MyObject.create(:foo => 'bar')
  MyObject.create(:foo => 'baz')
end