@Rei 成功了！是类型问题！谢谢各位解答！

@Rei @tumayun 刚刚外出了！在终端成功！

2.0.0-p0 :003 > p.update_attributes(:category_ids => [4,5,10])
  MOPED: 127.0.0.1:27017 COMMAND      database=admin command={:ismaster=>1} (0.3510ms)
  MOPED: 127.0.0.1:27017 UPDATE       database=meiyuewuyou_development collection=products selector={"_id"=>3} update={"$set"=>{"category_ids"=>[4, 5, 10], "updated_at"=>2013-04-28 11:48:22 UTC}} flags=[] (0.1547ms)
  MOPED: 127.0.0.1:27017 UPDATE       database=meiyuewuyou_development collection=categories selector={"$and"=>[{"_id"=>{"$in"=>[4, 5, 10]}}]} update={"$addToSet"=>{"product_ids"=>3}} flags=[:multi] (0.0887ms)
  MOPED: 127.0.0.1:27017 UPDATE       database=meiyuewuyou_development collection=categories selector={"$and"=>[{"_id"=>{"$in"=>[6, 9, 3]}}]} update={"$pull"=>{"product_ids"=>3}} flags=[:multi] (0.0861ms)
 => true
2.0.0-p0 :005 > p
 => #<Product _id: 3, _type: nil, created_at: 2013-04-27 01:37:21 UTC, updated_at: 2013-04-28 11:48:22 UTC, liked_user_ids: [], likes_count: 0, name: "干爽网面", howmany: nil, price: 0, exprice: 0, inprice: 0, size: "", use: nil, feature: "", inventory: 0, sales: 0, cover: 0, selling: true, barcode: "12121121212", special_offer: false, node_id: 1, manufacturer_id: 6, category_ids: [4, 5, 10], identifier: "", smell: "">

category_ids: [4, 5, 10]

@Rei

class Category
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::BaseModel

  field :name
  field :sort, :type => Integer, :default => 0

  belongs_to :node
  belongs_to :parent, :class_name => "Category"
  has_many :children, :class_name => "Category", :foreign_key => "parent_id", :dependent => :destroy
  has_and_belongs_to_many :products

  scope :roots, where(:parent_id => nil)
end

@Rei

# encoding: utf-8
class Product
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::BaseModel
  include Mongoid::CounterCache
  include Mongoid::Likeable

  field :name        #产品名称
  field :howmany,     :type => Integer#内含多少片
  field :price,             :type => Float, :default => 0  #销售价格
  field :exprice,         :type => Float, :default => 0  #超市价格
  field :inprice,          :type => Float, :default => 0  #入货价格
  field :size          #规格
  field :use           #用途
  field :feature    #产品特点
  field :inventory,      :type => Integer, :default => 0 #库存量
  field :sales,              :type => Integer, :default => 0 #销售量
  field :cover,             :type => Integer, :default => 0 #封面
  field :selling,           :type => Boolean, :default => true #在售
  field :barcode,         :default => "" #条形码
  field :special_offer, :type => Boolean, :default => false

  belongs_to :node, :inverse_of => :products
  belongs_to :manufacturer, :inverse_of => :products
  has_many :line_items
  has_many :pictures, :as => :imageable, :dependent => :destroy
  has_and_belongs_to_many :categories

  attr_accessible :name, :howmany, :price, :exprice, :inprice, :size, :smell, :use, :feature, :sales, :manufacturer_id, :cover, :identifier, :barcode, :selling, :inventory, :category_ids,:special_offer, :node_id

  validates_presence_of :manufacturer_id, :name
  validates_uniqueness_of :barcode, :name

  index :inventory => 1
  index :likes_count => 1

  scope :low_inventory, where(:inventory.lt => 5)
  scope :high_likes, desc(:likes_count, :_id)
  scope :popular, where(:likes_count.gt => 5)
  scope :sell, where(:selling => true)
  scope :special_offering, where(:special_offer => true)

  def format_selling
    self.selling ? "上架" : "下架"
  end

end

@Rei 我看看，我代码如下 product form

<div class="control-group">
  <label class="control-label">面质</label>
    <div class="controls">
      <label class="checkbox inline">
        <input id="product_category_ids_" name="product[category_ids][]" type="checkbox" value="2" />
        棉柔
      </label>
      <label class="checkbox inline">
        <input checked="checked" id="product_category_ids_" name="product[category_ids][]" type="checkbox" value="3" />
        网面
      </label>
    </div>
  </div>

products_controller.rb create

def create
  @product = Product.new(params[:product])

  if @product.save
    session[:admin_return_to] ||= cpanel_products_path
    redirect_to session[:admin_return_to], :notice => "保存成功!"
  else
    render :action => "new", :notice => "保存失败!"
  end
end

@saberma 请教下，你的 shopqi，商品和分类的设计思路是怎样的？是如何针对不同商品有不同分类进行设计？

@zfjoy520 如果不涉及到你项目的私密，可以详细分享是你是如何设计 product 和 category 的吗？

@zfjoy520 你的意思是不是用类的继承？

@ChanceDoor 不行呢，还是没数据！

@zfjoy520 那只有优化吧？但表的设计还是不变的啊

@zfjoy520 @ChanceDoor 我本来也是这种，这样做不能通用，淘宝那些应该也不是这样的。有不同的商品这种方法就不好使了，例如有鞋子和手机，他们的属性没一个相同，所以 product 这个 model 里面，没可能有这么多 xx_id 呢！

@ChanceDoor 我就是不知道应该怎么写，你的意思是把参数的数组，循环搜索？ @zfjoy520 是啊，就是这个功能！

@zfjoy520 恩，商品可能拥有更多 categories，例如 [3,7,12,6,8,9]! 顾客可能要筛选，[6,3,9]，所以要搜索出 products 中拥有 [6,3,9]categories 的 products，返回给顾客，product 和 category 是多对多的关联

@zfjoy520 是无序的，只有拥有 4,5,6 都符合！

@zfjoy520 你误会了！我不是要交集！我的意图是：几个商品，同时拥有 category_ids:["6","9","3"]！现在传入参数 category=6-3-9，然后把他转换成 array，传入 conditions，然后进行搜索！

@ChanceDoor {:node_id=>"1", :category_ids=>["9", "3", "6"]}这是 conditions！ 这是 product,category_ids: ["6", "9", "3"]

#<Product _id: 3, _type: nil, created_at: 2013-04-27 01:37:21 UTC, updated_at: 2013-04-28 03:38:38 UTC, liked_user_ids: [], likes_count: 0, name: "干爽网面", howmany: nil, price: 0, exprice: 0, inprice: 0, size: "", use: nil, feature: "", inventory: 0, sales: 0, cover: 0, selling: true, barcode: "12121121212", special_offer: false, node_id: 1, manufacturer_id: 6, category_ids: ["6", "9", "3"], identifier: "", smell: "">

@Rei

params[:product][:category_ids] = params[:product][:category_ids].map{|i| i.to_i}
logger.info(params[:product][:category_ids])

在 create 转换了为 i，但是保存到数据库还是 s，category_ids: ["5", "8", "3"]

conditions.merge!(:category_ids => params[:category].split("-").map{|i| i.to_s}) unless params[:category].blank?
logger.info(params[:category].split("-")) unless params[:category].blank?
logger.info(params[:category].split("-").map{|i| i.to_s}) unless params[:category].blank?
@products = Product.all(conditions).paginate(:page => params[:page], :per_page => 10)

而在搜索的时候转换，也没用！我用 logger.info 输出，不转换已经是 ["5", "8", "3"] 了，但是执行数据库搜索的时候，就会变成 [5, 8, 3]!

@Rei 因为是多对多，所以在 product 的表单里用 checkbox，他自动保存为字符

<%= check_box_tag "product[category_ids][]", category.id, @product.categories.map(&:id).include?(category.id) %>

@Rei 这样转换挺麻烦的？有办法在保存 product 数据时把它转换成整型保存吗？或者其他好办法？

@Rei 悲催！我看看！

@Teddy @lionzixuanyuan @Rei 谢谢！

MOPED: 127.0.0.1:27017 COMMAND      database=meiyuewuyou_development command={:count=>:products, :query=>{"category_ids"=>{"$all"=>[9, 2, 6]}}} (0.4029ms)

=> #<Product _id: 3, _type: nil, created_at: 2013-04-27 01:37:21 UTC, updated_at: 2013-04-27 05:30:24 UTC, liked_user_ids: [], likes_count: 0, name: "干爽网面", howmany: nil, price: 0, exprice: 0, inprice: 0, size: "", use: nil, feature: "", inventory: 0, sales: 0, cover: 0, selling: true, barcode: "12121121212", special_offer: false, node_id: 1, manufacturer_id: 6, category_ids: ["2", "6", "9"], identifier: "", smell: "">

但是搜索没结果，是不是category_ids有顺序限制？

@Teddy 要自己写语句？

@lukefan 多对多下，如果 params[:tag_id] 是一个 id 数组呢？就是 [1,2,3] 查询出同时有这个的 article!

@1272729223 有联系方式？

@1272729223 得闲试试！前端高手，膜拜！