rails 自增长

/lib/document_number.rb

class DocumentNumber  TIME_TO_WAIT = 1  def initialize(document)    @sequence = "#{document}_number_seq"  end  def get(time_prefix_format = '%y%m%d', number_of_digits = 6)    prefix      = Time.zone.now.strftime(time_prefix_format)    start_value = prefix + ('0' * number_of_digits)    next_value  = get_uncached_sequence    if start_value.to_i > next_value.to_i      set_value(start_value)      sleep(TIME_TO_WAIT)      next_value = get_uncached_sequence    end    next_value  end  def get_uncached_sequence    ActiveRecord::Base.uncached do      get_sequence    end  end  def get_sequence    next_value  rescue ActiveRecord::StatementInvalid => e # the sequence is not created yet    create_sequence    next_value  end  class << self    def get_order_number      number = new(:order).get('%y%m%d', 5)      "B#{number}"    end    def get_sub_order_number      number = new(:sub_order).get      "M#{number}"    end    def get_bill_number      "T#{new(:bill).get}"    end    def get_special_approval_number      "S#{new(:special_approval).get}"    end  end  private  def create_sequence    ActiveRecord::Base.connection.execute("create sequence #{@sequence}")  end  def next_value    ActiveRecord::Base.connection.select_value("select nextval('#{@sequence}')")  end  def set_value(value)    ActiveRecord::Base.connection.execute("select setval('#{@sequence}', #{value})")  endend

migration

def change  ActiveRecord::Base.connection.execute("create sequence crowdfunding_number_seq")end

config/application

config.autoload_paths << Rails.root.join('lib')

rails console

DocumentNumber=> DocumentNumber

说明已经可以用这个类
model/order.rb

before_create :save_order_number #保存后生成认筹编码  def save_order_number    self.order_number = DocumentNumber.get_order_number  end