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<h2>Active Model 基礎</h2><p>本篇教你如何開始使用 Model。 Active Model 允許 Action Pack 輔助方法與不是 Active Record 的 Model 類別來做互動。Active Model 也允許在 Rails 框架之外自己造 ORM。</p><p>讀完本篇，您將了解：</p>
<ul>
<li><code>AttributeMethods</code> 模組</li>
<li><code>Callbacks</code> 模組</li>
<li><code>Conversion</code> 模組</li>
<li><code>Dirty</code> 模組</li>
<li><code>Validations</code> 模組</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li>
<a href="#active-model-%E7%B0%A1%E4%BB%8B">Active Model 簡介</a>
<ul>
<li><a href="#attributemethods">AttributeMethods</a></li>
<li><a href="#%E5%9B%9E%E5%91%BC">回呼</a></li>
<li><a href="#conversion">Conversion</a></li>
<li><a href="#dirty">Dirty</a></li>
<li><a href="#%E9%A9%97%E8%AD%89">驗證</a></li>
<li><a href="#activemodel-naming">ActiveModel::Naming</a></li>
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<div id="mainCol">
<h3 id="active-model-簡介">1 Active Model 簡介</h3><p>Active Model 是一個函式庫，由許多用來與 Action Pack 互動的模組組成。以下簡單介紹幾個 Active Model 的模組。</p><h4 id="attributemethods">1.1 AttributeMethods</h4><p>用來給方法加上前綴或後綴。</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person
include ActiveModel::AttributeMethods
attribute_method_prefix 'reset_'
attribute_method_suffix '_highest?'
define_attribute_methods 'age'
attr_accessor :age
private
def reset_attribute(attribute)
send("#{attribute}=", 0)
end
def attribute_highest?(attribute)
send(attribute) > 100
end
end
person = Person.new
person.age = 110
person.age_highest? # true
person.reset_age # 0
person.age_highest? # false
</pre>
</div>
<h4 id="回呼">1.2 回呼</h4><p>Active Record 風格的回呼。讓我們可以在運行期定義回呼。定義回呼後便有 <code>before_*</code>、<code>after_*</code> 與 <code>around_*</code> 方法可用。</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person
extend ActiveModel::Callbacks
define_model_callbacks :update
before_update :reset_me
def update
run_callbacks(:update) do
# This method is called when update is called on an object.
end
end
def reset_me
# This method is called when update is called on an object as a before_update callback is defined.
end
end
</pre>
</div>
<h4 id="conversion">1.3 Conversion</h4><p>如果一個類別有定義 <code>persisted?</code> 與 <code>id</code> 方法，則你可引入 <code>Conversion</code> 模組，並對此類別的物件呼叫 Rails 的 conversion 方法（<code>to_model</code>、<code>to_key</code>、<code>to_param</code>）。</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person
include ActiveModel::Conversion
def persisted?
false
end
def id
nil
end
end
person = Person.new
person.to_model == person # => true
person.to_key # => nil
person.to_param # => nil
</pre>
</div>
<h4 id="dirty">1.4 Dirty</h4><p>物件有一個或多個改動，卻未儲存，則稱物件變“dirty”了。這讓我們可以檢查物件是否有變動。以下是 <code>Person</code> 類別，有 <code>first_name</code> 與 <code>last_name</code> 這兩個屬性：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
require 'active_model'
class Person
include ActiveModel::Dirty
define_attribute_methods :first_name, :last_name
def first_name
@first_name
end
def first_name=(value)
first_name_will_change!
@first_name = value
end
def last_name
@last_name
end
def last_name=(value)
last_name_will_change!
@last_name = value
end
def save
# do save work...
changes_applied
end
end
</pre>
</div>
<h5 id="查詢物件修改過屬性的列表">1.4.1 查詢物件修改過屬性的列表</h5><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
person = Person.new
person.changed? # => false
person.first_name = "First Name"
person.first_name # => "First Name"
# returns if any attribute has changed.
person.changed? # => true
# returns a list of attributes that have changed before saving.
person.changed # => ["first_name"]
# returns a hash of the attributes that have changed with their original values.
person.changed_attributes # => {"first_name"=>nil}
# returns a hash of changes, with the attribute names as the keys, and the values will be an array of the old and new value for that field.
person.changes # => {"first_name"=>[nil, "First Name"]}
</pre>
</div>
<h5 id="attribute-based-accessor-methods">1.4.2 Attribute based accessor methods</h5><p>檢查 <code>first_name</code> 這個屬性是否有變動，<code>first_name_changed?</code>：</p><p>Track whether the particular attribute has been changed or not.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# attr_name_changed?
person.first_name # => "First Name"
person.first_name_changed? # => true
</pre>
</div>
<p>檢查屬性上一次的數值：
Track what was the previous value of the attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# attr_name_was accessor
person.first_name_was # => "First Name"
</pre>
</div>
<p>檢查屬性上次與當前的值，有變化回傳 Array，沒變化回傳 <code>nil</code>：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# attr_name_change
person.first_name_change # => [nil, "First Name"]
person.last_name_change # => nil
</pre>
</div>
<h4 id="驗證">1.5 驗證</h4><p>給類別加入 Active Record 風格的驗證功能：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person
include ActiveModel::Validations
attr_accessor :name, :email, :token
validates :name, presence: true
validates_format_of :email, with: /\A([^\s]+)((?:[-a-z0-9]\.)[a-z]{2,})\z/i
validates! :token, presence: true
end
person = Person.new(token: "2b1f325")
person.valid? # => false
person.name = 'vishnu'
person.email = 'me'
person.valid? # => false
person.email = '[email protected]'
person.valid? # => true
person.token = nil
person.valid? # => raises ActiveModel::StrictValidationFailed
</pre>
</div>
<h4 id="activemodel-naming">1.6 ActiveModel::Naming</h4><p><code>Naming</code> 模組加入幾個幫助管理命名和路由的模組。這個模組定義了 <code>model_name</code> 類別方法，這個方法用 <code>ActiveSupport::Inflector</code> 定義了許多存取器（accessor）方法。</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person
extend ActiveModel::Naming
end
Person.model_name.name # => "Person"
Person.model_name.singular # => "person"
Person.model_name.plural # => "people"
Person.model_name.element # => "person"
Person.model_name.human # => "Person"
Person.model_name.collection # => "people"
Person.model_name.param_key # => "person"
Person.model_name.i18n_key # => :person
Person.model_name.route_key # => "people"
Person.model_name.singular_route_key # => "person"
</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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