计数器缓存不更新，但我可以保存到家长和孩子

Question

我添加了一个计数器缓存，但不能让它更新。但我可以更新父 - 加入了新的博客文章的博客帖子模型 - 我可以更新的孩子 - 加入了新的注释 - 评论模式。计数器缓存应该通过自动更新blog_posts.comments_count领域，以保持每个博客发表评论总数的轨道。我将概述一些我所经历的步骤，并希望有人会注意到这是我做错了。架构转储末。

我有博客Post模型：

class Post < ActiveRecord::Base
  set_table_name("blog_posts")
  belongs_to :author, :class_name => "User", :foreign_key => 'author_id'
  has_many :comments, :class_name => "Comment",
    :foreign_key => 'post_id', :order => "created_at desc", :dependent => :destroy
  has_many :categorizations
  has_many :categories, :through => :categorizations
  named_scope :recent, :order => "created_at desc", :limit => 5

end

和与设置到柱模型中的一个counter_cache评论模型：

class Comment < ActiveRecord::Base
  belongs_to :post, :class_name => "Post", :foreign_key => "post_id", :counter_cache => true
  belongs_to :author, :class_name => "User", :foreign_key => "author_id"
end

我创建迁移添加counter_cache列到blog_posts表：

class AddCommentCounter < ActiveRecord::Migration
  def self.up
    add_column :blog_posts, :comments_count, :integer, :limit => 4, :default => 0, :null => false
    Post.find(:all).each do |post|
      current_count = post.comments.size
      post.update_attribute(:comments_count, current_count)
    end
  end

  def self.down
    remove_column :blog_posts, :comments_count
  end
end

但迁移失败更新与CURRENT_COUNT的博客文章。它总是零。

我打开了的Rails控制台尝试手动update_attribute：

Loading development environment (Rails 2.3.2)

>> p = Post.find 1
p = Post.find 1

=> #<Post id: 1, title: "test", content: "test", author_id: 1, status: "ok", created_at: "2009-05-21 19:27:14", updated_at: "2009-05-24 07:02:35", comments_count: 0>

>> p.comments
p.comments

=> [#<Comment id: 5, post_id: 1, author_id: 1, content: "Fifth Comment", status: "ok", created_at: "2009-05-24 07:08:56", updated_at: "2009-05-24 07:08:56">, #<Comment id: 4, post_id: 1, author_id: 1, content: "Fourth Comment", status: "ok", created_at: "2009-05-24 07:05:32", updated_at: "2009-05-24 07:05:32">, #<Comment id: 3, post_id: 1, author_id: 1, content: "Third Comment", status: "ok", created_at: "2009-05-24 06:34:59", updated_at: "2009-05-24 06:34:59">, #<Comment id: 2, post_id: 1, author_id: 1, content: "Second Comment", status: "ok", created_at: "2009-05-24 05:20:43", updated_at: "2009-05-24 05:20:43">, #<Comment id: 1, post_id: 1, author_id: 1, content: "First Comment", status: "ok", created_at: "2009-05-21 19:27:14", updated_at: "2009-05-21 19:27:14">]


>> p.comments.size
p.comments.size

=> 5

>> p.comments_count
p.comments_count

=> 0

>> p.update_attribute(:comments_count, 5)
p.update_attribute(:comments_count, 5)

=> true

>> p.comments_count
p.comments_count

=> 5

>> p.save
p.save

=> true

但是，当我看在数据库comments_count = 0。

任何想法将超过欢快理解。

我schema.db看起来像这样：

ActiveRecord::Schema.define(:version => 20090524055907) do

  create_table "blog_posts", :force => true do |t|
    t.string   "title",          :limit => 100, :default => "", :null => false
    t.text     "content",                                       :null => false
    t.integer  "author_id",                     :default => 0,  :null => false
    t.string   "status",         :limit => 20,  :default => "", :null => false
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "comments_count",                :default => 0,  :null => false
  end

  add_index "blog_posts", ["author_id"], :name => "index_blog_posts_on_author_id"

  create_table "categories", :force => true do |t|
    t.string   "name",        :limit => 50, :default => "", :null => false
    t.string   "short_name",  :limit => 30, :default => "", :null => false
    t.string   "description",               :default => "", :null => false
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "categories_posts", :force => true do |t|
    t.integer "category_id", :null => false
    t.integer "post_id",     :null => false
  end

  add_index "categories_posts", ["category_id"], :name => "index_categories_posts_on_category_id"
  add_index "categories_posts", ["post_id"], :name => "index_categories_posts_on_post_id"

  create_table "comments", :force => true do |t|
    t.integer  "post_id",                  :default => 0,  :null => false
    t.integer  "author_id",                :default => 0,  :null => false
    t.text     "content",                                  :null => false
    t.string   "status",     :limit => 25, :default => "", :null => false
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "sessions", :force => true do |t|
    t.string   "session_id", :default => "", :null => false
    t.text     "data"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  add_index "sessions", ["session_id"], :name => "index_sessions_on_session_id"
  add_index "sessions", ["updated_at"], :name => "index_sessions_on_updated_at"

  create_table "users", :force => true do |t|
    t.string   "username",        :limit => 25, :default => "", :null => false
    t.string   "hashed_password", :limit => 40, :default => "", :null => false
    t.string   "first_name",      :limit => 25, :default => "", :null => false
    t.string   "last_name",       :limit => 40, :default => "", :null => false
    t.string   "email",           :limit => 50, :default => "", :null => false
    t.string   "display_name",    :limit => 25, :default => "", :null => false
    t.integer  "user_level",      :limit => 3,  :default => 0,  :null => false
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end

Answer 1

看一看从更新的代码railscasts插曲23 上counter_cache。

在计数器属性是attr_readonly。也许更新计数器是你需要的地方更新的属性用什么在迁移？