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<h2>Active Job 基礎</h2><p>本篇提供所有建立任務、將任務加入排程，執行背景任務的所有知識。</p><p>讀完本篇，您將了解：</p>
<ul>
<li>如何新建任務。</li>
<li>如何把任務加入排程。</li>
<li>如何在背景執行任務。</li>
<li>如何異步發送信件。</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li><a href="#%E7%B0%A1%E4%BB%8B">簡介</a></li>
<li><a href="#active-job-%E5%AD%98%E5%9C%A8%E7%9B%AE%E7%9A%84">Active Job 存在目的</a></li>
<li>
<a href="#%E6%96%B0%E5%BB%BA%E4%BB%BB%E5%8B%99">新建任務</a>
<ul>
<li><a href="#%E5%BB%BA%E7%AB%8B%E4%BB%BB%E5%8B%99">建立任務</a></li>
<li><a href="#%E4%BB%BB%E5%8B%99%E6%8E%92%E7%A8%8B">任務排程</a></li>
</ul>
</li>
<li>
<a href="#%E5%9F%B7%E8%A1%8C%E4%BB%BB%E5%8B%99">執行任務</a>
<ul>
<li><a href="#%E5%BE%8C%E5%8F%B0">後台</a></li>
<li><a href="#%E5%88%87%E6%8F%9B%E5%BE%8C%E5%8F%B0">切換後台</a></li>
</ul>
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<li><a href="#%E4%BD%87%E5%88%97">佇列</a></li>
<li>
<a href="#%E5%9B%9E%E5%91%BC">回呼</a>
<ul>
<li><a href="#%E5%8F%AF%E7%94%A8%E7%9A%84%E5%9B%9E%E5%91%BC">可用的回呼</a></li>
<li><a href="#%E7%94%A8%E6%B3%95">用法</a></li>
</ul>
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<li><a href="#actionmailer">ActionMailer</a></li>
<li><a href="#globalid">GlobalID</a></li>
<li><a href="#exceptions">Exceptions</a></li>
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<h3 id="簡介">1 簡介</h3><p>Active Job 是用來宣告任務，並把任務放到多種佇列後台執行的框架。這些任務可以是平常的系統定時清理、收費方式改變通知、或是定時寄送郵件等任務。任何可以細分的工作與同步執行的事情都可以用 Active Job 來做。</p><h3 id="active-job-存在目的">2 Active Job 存在目的</h3><p>主要確保 Rails 應用程式有個一致的背景任務框架，不做背景任務，要即時執行也可以。接著便可以有基於 Active Job 打造的功能、Gem 誕生，而無需擔心各種佇列後台，像是 Delayed Job 和 Resque 之間的 API 差異。選擇佇列後台變成一種運維方面的考量，而切換後台也無需修改任務本身的實作。</p><h3 id="新建任務">3 新建任務</h3><p>本節提供建立任務，將任務加入排程的詳細教學。</p><h4 id="建立任務">3.1 建立任務</h4><p>Active Job 提供了 Rails 產生器來建立任務。以下會在 <code>app/jobs</code> 建立一件新任務：</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ bin/rails generate job guests_cleanup
create app/jobs/guests_cleanup_job.rb
</pre>
</div>
<p>也可以建立跑在特定佇列上的任務：</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ bin/rails generate job guests_cleanup --queue urgent
create app/jobs/guests_cleanup_job.rb
</pre>
</div>
<p>可以看出來，建立任務就和使用其他的 Rails 產生器一樣簡單。</p><p>若不想使用產生器，也可以自己在 <code>app/jobs</code> 下建立檔案，只要確保任務是繼承自 <code>ActiveJob::Base</code> 的類別即可。</p><p>以下是任務的程式範例：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class GuestsCleanupJob < ActiveJob::Base
queue_as :default
def perform
# Do something later
end
end
</pre>
</div>
<h4 id="任務排程">3.2 任務排程</h4><p>將任務加入排程：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
MyJob.enqueue record # Enqueue a job to be performed as soon the queueing system is free.
</pre>
</div>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
MyJob.enqueue_at Date.tomorrow.noon, record # Enqueue a job to be performed tomorrow at noon.
</pre>
</div>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
MyJob.enqueue_in 1.week, record # Enqueue a job to be performed 1 week from now.
</pre>
</div>
<p>就這麼簡單！</p><h3 id="執行任務">4 執行任務</h3><p>若無設定連接器，任務會即刻執行。</p><h4 id="後台">4.1 後台</h4><p>Active Job 針對提供以下佇列後台的連接器：</p>
<ul>
<li><a href="https://github.com/nesquena/backburner">Backburner</a></li>
<li><a href="https://github.com/collectiveidea/delayed_job">Delayed Job</a></li>
<li><a href="https://github.com/bkeepers/qu">Qu</a></li>
<li><a href="https://github.com/chanks/que">Que</a></li>
<li><a href="https://github.com/ryandotsmith/queue_classic">QueueClassic</a></li>
<li><a href="https://github.com/resque/resque">Resque 1.x</a></li>
<li><a href="https://github.com/mperham/sidekiq">Sidekiq</a></li>
<li><a href="https://github.com/jondot/sneakers">Sneakers</a></li>
<li><a href="https://github.com/brandonhilkert/sucker_punch">Sucker Punch</a></li>
</ul>
<h5 id="各後台功能特色">4.1.1 各後台功能特色</h5>
<table>
<thead>
<tr>
<th></th>
<th>Async</th>
<th>Queues</th>
<th>Delayed</th>
<th>Priorities</th>
<th>Timeout</th>
<th>Retries</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>Backburner</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
<td>Job</td>
<td>Global</td>
</tr>
<tr>
<td><strong>Delayed Job</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
<td>Job</td>
<td>Global</td>
<td>Global</td>
</tr>
<tr>
<td><strong>Que</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
<td>Job</td>
<td>No</td>
<td>Job</td>
</tr>
<tr>
<td><strong>Queue Classic</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Gem</td>
<td>No</td>
<td>No</td>
<td>No</td>
</tr>
<tr>
<td><strong>Resque</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Gem</td>
<td>Queue</td>
<td>Global</td>
<td>?</td>
</tr>
<tr>
<td><strong>Sidekiq</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
<td>Queue</td>
<td>No</td>
<td>Job</td>
</tr>
<tr>
<td><strong>Sneakers</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>No</td>
<td>Queue</td>
<td>Queue</td>
<td>No</td>
</tr>
<tr>
<td><strong>Sucker Punch</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
<td>No</td>
<td>No</td>
<td>No</td>
</tr>
<tr>
<td><strong>Active Job</strong></td>
<td>Yes</td>
<td>Yes</td>
<td>WIP</td>
<td>No</td>
<td>No</td>
<td>No</td>
</tr>
<tr>
<td><strong>Active Job Inline</strong></td>
<td>No</td>
<td>Yes</td>
<td>N/A</td>
<td>N/A</td>
<td>N/A</td>
<td>N/A</td>
</tr>
</tbody>
</table>
<h4 id="切換後台">4.2 切換後台</h4><p>切換後台的連接器非常簡單：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# be sure to have the adapter gem in your Gemfile and follow the adapter specific
# installation and deployment instructions
YourApp::Application.config.active_job.queue_adapter = :sidekiq
</pre>
</div>
<h3 id="佇列">5 佇列</h3><p>多數的連接器都支持多種佇列。用 Active Job 可以將任務放到特定的佇列裡執行：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class GuestsCleanupJob < ActiveJob::Base
queue_as :low_priority
#....
end
</pre>
</div>
<div class="note"><p>確保後台程式知道佇列的名稱是什麼。某些後台可能需要明確指定佇列。</p></div><h3 id="回呼">6 回呼</h3><p>Active Job 在任務生命週期裡的每個階段都有提供 hooks。回呼允許在任務生命週期裡觸發事件來執行程式邏輯。</p><h4 id="可用的回呼">6.1 可用的回呼</h4>
<ul>
<li>before_enqueue</li>
<li>around_enqueue</li>
<li>after_enqueue</li>
<li>before_perform</li>
<li>around_perform</li>
<li>after_perform</li>
</ul>
<h4 id="用法">6.2 用法</h4><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class GuestsCleanupJob < ActiveJob::Base
queue_as :default
before_enqueue do |job|
# do somthing with the job instance
end
around_perform do |job, block|
# do something before perform
block.call
# do something after perform
end
def perform
# Do something later
end
end
</pre>
</div>
<h3 id="actionmailer">7 ActionMailer</h3><p>現代網路應用最常見的任務之一是在請求響應週期之外發送 Email，減去使用者等待的時間。Active Job
已與 Action Mailer 整合，異步寄送信件只需使用 <code>deliver_later</code> 即可：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Instead of the classic
UserMailer.welcome(@user).deliver
# use #deliver later to send the email async
UserMailer.welcome(@user).deliver_later
</pre>
</div>
<h3 id="globalid">8 GlobalID</h3><p>Active Job 支持使用 GlobalID 作為參數。這使得任務可以傳入 Active Record 物件，而不只是需要額外處理的類別名稱或 ID。使用類別和 ID 的任務看起來會像是：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class TrashableCleanupJob
def perform(trashable_class, trashable_id, depth)
trashable = trashable_class.constantize.find(trashable_id)
trashable.cleanup(depth)
end
end
</pre>
</div>
<p>可以傳入 Active Record 物件來簡化：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class TrashableCleanupJob
def perform(trashable, depth)
trashable.cleanup(depth)
end
end
</pre>
</div>
<p>以上對任何混入 <code>ActiveModel::GlobalIdentification</code> 的類都有效，Active Model 的類別預設皆有混入 <code>ActiveModel::GlobalIdentification</code>。</p><h3 id="exceptions">9 Exceptions</h3><p>Active Job 提供捕捉任務執行期間發生異常的方法：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class GuestsCleanupJob < ActiveJob::Base
queue_as :default
rescue_from(ActiveRecord:NotFound) do |exception|
# do something with the exception
end
def perform
# Do something later
end
end
</pre>
</div>
<h3>反饋</h3>
<p>
歡迎幫忙改善指南的品質。
</p>
<p>
如發現任何錯誤之處，歡迎修正。開始貢獻前，可以先閱讀<a href="http://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#contributing-to-the-rails-documentation">貢獻指南：文件</a>。
</p>
<p>翻譯如有錯誤，深感抱歉，歡迎 <a href="https://github.com/docrails-tw/guides/fork">Fork</a> 修正，或至此處<a href="https://github.com/docsrails-tw/guides/issues/new">回報</a>。</p>
<p>
文章可能有未完成或過時的內容。請先檢查 <a href="http://edgeguides.rubyonrails.org">Edge Guides</a> 來確定問題在 master 是否已經修掉了。再上 master 補上缺少的文件。內容參考 <a href="ruby_on_rails_guides_guidelines.html">Ruby on Rails 指南準則</a>來了解行文風格。
</p>
<p>最後，任何關於 Ruby on Rails 文件的討論，歡迎至 <a href="http://groups.google.com/group/rubyonrails-docs">rubyonrails-docs 郵件論壇</a>。
</p>
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