active_record.rb

class ActiveRecord::Base

  def self.import!(record_list)
    raise ArgumentError 'record_list not an Array of Hashes' unless record_list.is_a?(Array) && record_list.all? {|rec| rec.is_a? Hash }
    return if record_list.empty?

    record_list.in_groups_of(1000, false).each do |record_group|
      key_list, value_list = convert_record_list(record_group)
      sql = "INSERT INTO #{self.table_name} (#{key_list.join(', ')}) VALUES #{value_list.map {|rec| "(#{rec.join(', ')})" }.join(' ,')}"
      self.connection.insert_sql(sql)
    end

    true
  end

  def self.convert_record_list(record_list)
    # Build the list of keys
    key_list = record_list.map(&:keys).flatten.map(&:to_s).uniq.sort

    value_list = record_list.map do |rec|
      list = []
      key_list.each {|key| list <<  ActiveRecord::Base.connection.quote(rec[key] || rec[key.to_sym]) }
      list
    end

    # If table has standard timestamps and they're not in the record list then add them to the record list
    time = ActiveRecord::Base.connection.quote(Time.now)
    for field_name in %w(created_at updated_at)
      if self.column_names.include?(field_name) && !(key_list.include?(field_name))
        key_list << field_name
        value_list.each {|rec| rec << time }
      end
    end

    return [key_list, value_list]
  end
end

Originial was off by one. I decided to use in_groups_of instead of ranges