发现 Rails 2.3.4 级联删除时加了记录锁验证

rails demo && cd demo
ruby script/generate model Post title:string body:text lock_version:integer 
# 注意进入 migrate lock_version 后面加 :default => 0
ruby script/generate model Comment body:text post_id:integer
rake db:migrate

model里配置 Post has many comments, 代码如下:

class Post < ActiveRecord::Base
  has_many :comments, :dependent => :destroy
end

class Comment < ActiveRecord::Base
  belongs_to :post

  after_destroy :change_post_title!

  protected

    def change_post_title!
      self.post.update_attributes!(:title => "new title")
    end
end

进入console, 执行如下代码:

post = Post.new(:title => 'title')
post.comments.build(:body => 'comment1')
post.comments.build(:body => 'comment1')
post.save

Post.last.destroy  # => ActiveRecord::StaleObjectError: Attempted to delete a stale object

Log记录:

Post Create (0.2ms)   INSERT INTO "posts" ("created_at", "title", "body", "updated_at", "lock_version") VALUES('2009-11-18 09:12:48', 'title', NULL, '2009-11-18 09:12:48', 0)
Comment Create (0.1ms)   INSERT INTO "comments" ("created_at", "body", "updated_at", "post_id") VALUES('2009-11-18 09:12:48', 'comment1', '2009-11-18 09:12:48', 6)
Comment Create (0.1ms)   INSERT INTO "comments" ("created_at", "body", "updated_at", "post_id") VALUES('2009-11-18 09:12:48', 'comment1', '2009-11-18 09:12:48', 6)
Post Load (0.3ms)   SELECT * FROM "posts" ORDER BY posts.id DESC LIMIT 1
Comment Load (0.3ms)   SELECT * FROM "comments" WHERE ("comments".post_id = 6)
Comment Destroy (0.2ms)   DELETE FROM "comments" WHERE "id" = 9
Post Load (0.2ms)   SELECT * FROM "posts" WHERE ("posts"."id" = 6)
Post Update with optimistic locking (0.1ms)    UPDATE "posts"
SET "updated_at" = '2009-11-18 09:12:54', "title" = 'new title', "lock_version" = 1 WHERE id = 6 AND "lock_version" = 0
Comment Destroy (0.1ms)   DELETE FROM "comments" WHERE "id" = 10
Post Load (0.2ms)   SELECT * FROM "posts" WHERE ("posts"."id" = 6)
Post Destroy (0.1ms)   DELETE FROM "posts" WHERE "id" = 6 AND "lock_version" = 0

通过log记录分析就能明白. 假如主类有lock_version字段做子类的级联删除, Rails 2.3.4 已经加了表记录锁.