find_or_create_by_XX

已存在的数据，执行更新，如果没有存在，则插入数据。

view:
<%=g.d f.select "#{d[:cityid]}-#{d[:device_manu]}",[["",""],["TL1","tl1"],["SNMP","snmp"]], {:selected =>d[:means] }%>

model:
def self.update_collect_means(collect_means)
      collect_means.each_pair do |id,means|
      update_all("id='#{id}'","means = '#{means}'")
    end
  end

controller:
  def update_collect_means
    params[:collect_means].each_pair do |id,means|
      unless means.blank?
        keys = id.split("-")
        #collect_mean = CollectMean.new(:cityid => keys[0],:device_manu => keys[1],:means => "#{means}")
        collect_mean =     CollectMean.find_or_create_by_cityid_and_device_manu_and_means(:cityid => keys[0], :device_manu => keys[1],:means => "#{means}")
        collect_mean.save
      end
    end
    #CollectMean.update_collect_means(params[:collect_means])
    flash[:notice] = "更新采集方式成功。"
    redirect_to :action => :index
  end