fohow_admin/app/models/live_broad.rb

class LiveBroad < ActiveRecord::Base
    has_paper_trail
    self.table_name = "live_broads"
    validates :room_id,:title, presence: true
    attr_accessor :v_cover
    before_save :before_save

    def before_save
      #自动取消其他置顶项
      if self.show
        live_broads = LiveBroad.find_by_sql("select * from live_broads ")
        # 创建商品图片
        live_broads.each do |l|
          if l.id != self.id
            l.show=false
            l.save
          end
        end
      end
    end

    IMG_STORE_PATH = "live_broads"

    rails_admin do
        navigation_label '直播管理'
        weight -100
        list do 
          filters [:id,:title]
          field :id      
          field :title
          field :room_id
          field :cover do
            formatted_value do
              bindings[:view].tag(:img,{:src => bindings[:object].get_cover_img,
              :style => 'width: 100px;height: 100px;cursor: pointer;display: block;max-width: 100px',
              :onClick => "javascript:window.open('#{bindings[:object].get_cover_img}')"})
            end
          end
          field :begin_time
          field :end_time
          field :show
          field :recommend
          field :remark
          field :created_at

        end

        show do
          field :id
          field :title
          field :room_id
          field :cover do
            formatted_value do
              bindings[:view].tag(:img,{:src => bindings[:object].get_cover_img,
              :style => 'width: 100px;height: 100px;cursor: pointer;display: block;max-width: 100px',
              :onClick => "javascript:window.open('#{bindings[:object].get_cover_img}')"})
            end
          end
          field :begin_time
          field :end_time
          field :show
          field :recommend
          field :remark
          field :created_at
          field :updated_at
        end

        edit do
          field :title
          field :room_id
          field :v_cover, :file_upload do
            pretty_value do
              bindings[:view].tag(:img, {:src => bindings[:object].get_cover_img, :class => 'preview'})
            end
          end
          field :begin_time
          field :end_time
          field :show
          field :recommend
          field :remark
        end
    end

    def get_cover_img
      url = "http://#{Ali::Oss::CDN_URL_FOR_HOST}/#{self.cover}"
      return url
    end

    def v_cover=file
      unless file.blank?
        clear_cover_img
        file_name = "#{UUID.new.generate[0...8].downcase}.jpg"
        file_path = "#{IMG_STORE_PATH}/#{file_name}"
        Ali::Oss.store(Ali::Oss::BUCKET_NAME_PUBLIC_READ, file_path, file.read)
        self.cover = file_path
        self.save
      end
    end

    def clear_cover_img
      file_path = "#{self.cover}"
      Ali::Oss.delete_object(Ali::Oss::BUCKET_NAME_PUBLIC_READ, file_path)
    end

    def after_destroy
      clear_cover_img
    end
end