写了一个 Reindex module 代码如下，功能就是在 ActiveRecord 对象 save 时，异步创建索引
module Reindex
def async_reindex
AsyncIndexJob.perform_later(self.class.to_s, self.id)
end
def self.included(base)
base.class_eval do
base.send :after_save ,:async_reindex
end
end
end
测试代码
require 'rails_helper'
RSpec.describe AsyncIndexJob, type: :job do
include ActiveJob::TestHelper
describe "AsyncIndexJob" do
it "should enqueue" do
group = Group.create(……)
expect(enqueued_jobs.size).to eq(1)
end
end
end
但是结果非常奇怪，queue 的 size 是 3，也就是 after_save 被调用了 3 次，为什么会这样呢？
Failures:
1) AsyncIndexJob AsyncIndexJob should enqueue
Failure/Error: expect(enqueued_jobs.size).to eq(1)
expected: 1
got: 3
补充一下 如果把 base.send :after_save ,:async_reindex 改成 base.send :after_create ,:async_reindex，那么 queue 的 size 是 2， 再改成 base.send :after_commit ,:async_reindex，queue 的 size 是 0，我懵的不行。
发现是 active_record 的问题 坑！ 在新建我的 Group Model 时，执行了三次 save 操作，第一次插入一个 group，然后插入一个 GroupAccount，然后更新 group 的值，加入了 member_count。
···
SQL (8.6ms) INSERT INTO groups (type, name, description, logo, creator_id, status, formal_type, talk_count, subject_count, recommend_count, posts_count, active_member_count, games_count, subs_count, created_at, updated_at) VALUES ('Groups::GameGroup', 'funn', 'hi', 'logo', 262763, 0, 0, 0, 0, 0, 0, 0, 0, 0, '2015-11-08 23:31:24', '2015-11-08 23:31:24')
SQL (1.7ms) INSERT INTO groups_accounts (group_id, talk_count, subject_count, recommend_count, post_count, account_id, created_at, updated_at) VALUES (2086, 0, 0, 0, 0, 262763, '2015-11-08 23:31:24', '2015-11-08 23:31:24')
SQL (0.9ms) UPDATE groups SET type = 'Groups::GameGroup', name = 'funn', description = 'hi', logo = 'logo', creator_id = 262763, status = 0, formal_type = 0, talk_count = 0, subject_count = 0, recommend_count = 0, posts_count = 0, active_member_count = 0, subs_count = 0, created_at = '2015-11-08 23:31:24', updated_at = '2015-11-08 23:31:24', id = 2086, member_count = 1 WHERE groups.id = 2086
···
The First Rule of Programming: It's Always Your Fault http://blog.codinghorror.com/the-first-rule-of-programming-its-always-your-fault/
你扩展了 ActiveRecord::Base，然后你跟我说是 ActiveRecord 的锅，ActiveRecord 表示不服。 来吃了这碗教程：http://guides.rubyonrails.org/active_record_callbacks.html