blocks|key|5590102|text|不是Rails修复，但您可以使用面向对象设计的NullObject模式来重构您的代码，以不同的方式处理"nil“。该模式基本上意味着您为一个对象创建一个null/nil类，该对象在为nil时进行处理。它有一些缺点:一个额外的类需要维护，当你添加新的方法时，你必须记得编辑空的类，这可能是零。好处是它把条件句移出了视图。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5590103|这里有一篇关于这个主题的很好的博客文章：http://robots.thoughtbot.com/post/20907555103/rails-refactoring-example-introduce-null-object|offset|length|5590104|另一个建议是把条件句移出你的视线，移到帮助器中。帮助器是包含视图逻辑的简单模块。我经历过视图的所有逻辑都在视图中，这使得视图代码很快就变得一团糟。|5590105|entityMap|0|LINK|mutability|MUTABLE|url|http://robots.thoughtbot.com/post/20907555103/rails-refactoring-example-introduce-null-object^0|0|K|2L|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@$D|R|E|S|1|T]]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

Not a Rails fix, but you can use the NullObject pattern of object oriented design to refactor your code to handle "nil" differently. The pattern basically means that you create a null/nil class for an object that handles when it is nil. It has some downsides: an extra class to maintain and you have to remember to edit the null class when you add new methods which may be nil. The good is that it moves the conditionals out of the view.

Here's a good blog post on the subject:
<a href="http://robots.thoughtbot.com/post/20907555103/rails-refactoring-example-introduce-null-object" rel="nofollow">http://robots.thoughtbot.com/post/20907555103/rails-refactoring-example-introduce-null-object</a>

Another suggestion would be to move the conditionals out of your view and into helpers. Helpers are simple modules that contain view logic. I've suffered through views with all their logic in the view and it makes the view code a mess very quickly.

blocks|key|5590265|text|你真的应该放置一些foreign+key+constraints和after_destroy+methods+on+your+associations。这将阻止您的数据库进入不一致状态。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|5590266|但是除了重构之外，你还应该检查一下ActiveSupport以及它对ruby所做的各种补充。参见http://guides.rubyonrails.org/active_support_core_extensions.html。|5590267|有三种方法可用于任何对象，我认为它们会对您有所帮助：|5590268|5590269|blank?+-如果对象为nil、空？、假和其他条件，则返回true。有关更好的explanation.|unordered-list-item|style|CODE|5590270|present?，请参阅the+documentation+-如果对象不为nil，不为空，则返回true？或者是真的。有关更好的explanation.|5590271|try(:foo)，请参见the+documentation+-尝试在对象上调用方法foo，如果对象为nil，则返回nil。有关更好的explanation.|5590272|，请参阅the+documentation|5590273|这样，您的示例代码可以是：|5590274|<td><%25=+location.parent.try(:name)+%25></td>
<td><%25=+location.parent.try(:client_name)+%25></td>|code-block|syntax|javascript|5590275|我真的建议你看看为什么你期望一个对象不是空的。迁移中的Foreign+key+constraints和after_destroy+hooks+for+your+associations将对此有所帮助。|5590276|entityMap|0|LINK|mutability|MUTABLE|url|http://guides.rubyonrails.org/migrations.html#active-record-and-referential-integrity|1|http://guides.rubyonrails.org/association_basics.html#association-callbacks|2|http://guides.rubyonrails.org/active_support_core_extensions.html|3|http://guides.rubyonrails.org/active_support_core_extensions.html#blank-and-present|4|5|http://guides.rubyonrails.org/active_support_core_extensions.html#try|6|7^0|9|N|0|X|16|1|0|1C|1T|2|0|0|0|0|6|0|0|8|C|H|3|0|0|9|16|3|D|H|4|0|4|H|5|0|0|0|R|N|6|1F|15|7|0^^$0|@$1|2|3|4|5|6|7|1L|8|@]|9|@$A|1M|B|1N|1|1O]|$A|1P|B|1Q|1|1R]]|C|$]]|$1|D|3|E|5|6|7|1S|8|@]|9|@$A|1T|B|1U|1|1V]]|C|$]]|$1|F|3|G|5|6|7|1W|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1X|8|@]|9|@]|C|$]]|$1|I|3|J|5|K|7|1Y|8|@$A|1Z|B|20|L|M]]|9|@]|C|$]]|$1|N|3|O|5|K|7|21|8|@$A|22|B|23|L|M]]|9|@$A|24|B|25|1|26]]|C|$]]|$1|P|3|Q|5|K|7|27|8|@$A|28|B|29|L|M]|$A|2A|B|2B|L|M]]|9|@$A|2C|B|2D|1|2E]]|C|$]]|$1|R|3|S|5|6|7|2F|8|@]|9|@$A|2G|B|2H|1|2I]]|C|$]]|$1|T|3|U|5|6|7|2J|8|@]|9|@]|C|$]]|$1|V|3|W|5|X|7|2K|8|@]|9|@]|C|$Y|Z]]|$1|10|3|11|5|6|7|2L|8|@]|9|@$A|2M|B|2N|1|2O]|$A|2P|B|2Q|1|2R]]|C|$]]|$1|12|3|-4|5|6|7|2S|8|@]|9|@]|C|$]]]|13|$14|$5|15|16|17|C|$18|19]]|1A|$5|15|16|17|C|$18|1B]]|1C|$5|15|16|17|C|$18|1D]]|1E|$5|15|16|17|C|$18|1F]]|1G|$5|15|16|17|C|$18|1F]]|1H|$5|15|16|17|C|$18|1I]]|1J|$5|15|16|17|C|$18|19]]|1K|$5|15|16|17|C|$18|1B]]]]

You should really place some <a href="http://guides.rubyonrails.org/migrations.html#active-record-and-referential-integrity" rel="nofollow">foreign key constraints</a> and <a href="http://guides.rubyonrails.org/association_basics.html#association-callbacks" rel="nofollow">after_destroy methods on your associations</a>. This will stop your database getting into a inconsistant state.

But aside from that refactor you should checkout ActiveSupport and the various additions it makes to ruby. See <a href="http://guides.rubyonrails.org/active_support_core_extensions.html" rel="nofollow">http://guides.rubyonrails.org/active_support_core_extensions.html</a>.

There are three methods which are available on any object which I think would be helpful to you:

<ul>
<li><code>blank?</code> - Returns true if the object is nil, empty?, false and other conditions. See <a href="http://guides.rubyonrails.org/active_support_core_extensions.html#blank-and-present" rel="nofollow">the documentation</a> for a better explanation.</li>
<li><code>present?</code> - Returns true if the object is not nil, not empty? or true. See <a href="http://guides.rubyonrails.org/active_support_core_extensions.html#blank-and-present" rel="nofollow">the documentation</a> for a better explanation.</li>
<li><code>try(:foo)</code> - Attempts to call the method <code>foo</code> on the object, returns nil if the object is nil. See <a href="http://guides.rubyonrails.org/active_support_core_extensions.html#try" rel="nofollow">the documentation</a> for a better explanation.</li>
</ul>

With this your sample code could be:

<pre><code>&lt;td&gt;&lt;%= location.parent.try(:name) %&gt;&lt;/td&gt;
&lt;td&gt;&lt;%= location.parent.try(:client_name) %&gt;&lt;/td&gt;
</code></pre>

I would really recommend that you have a look at why you are expecting an object to not be nil. <a href="http://guides.rubyonrails.org/migrations.html#active-record-and-referential-integrity" rel="nofollow">Foreign key constraints</a> in your migration and <a href="http://guides.rubyonrails.org/association_basics.html#association-callbacks" rel="nofollow">after_destroy hooks for your associations</a> will help with this.

I've been learning Rails for the past 6 months. I think it's great! 

But, 99% of errors my app gets are nil errors. I'm either trying to display a field that is nil or a foreign key is pointing to a record that has been deleted. 

I have this type of code in many places:

<pre><code> &lt;% if location.parent != nil %&gt;
 &lt;td&gt;&lt;%= location.parent.name %&gt;&lt;/td&gt;
 &lt;% else %&gt;
 &lt;td&gt;&lt;/td&gt;
 &lt;% end %&gt;

 &lt;% if location.client_id != nil %&gt;
 &lt;td&gt;&lt;%= location.client.client_name %&gt;&lt;/td&gt;
 &lt;% else %&gt;
 &lt;td&gt;&lt;/td&gt;
 &lt;% end %&gt;
</code></pre>

I really wish Rails would just show a blank when the field is nil! Or, set a flash with an error and still show the page. Instead, the page bombs. On Heroku, you get the "Sorry, somethings wrong...."

Is there any way to better handle blank fields? Is there a better way to code the above? Is there some Rails setting I'm not aware of? Is there a gem to handle these type of errors?

Rails nil errors - any way to stop them?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在过去的6个月里，我一直在学习Rails。我觉得这很棒！但是，我的应用收到的99%的错误都是零错误。我正在尝试显示一个为空的字段，或者有一个外键指向已被删除的记录。我在很多地方都有这种类型的代码： <% if location.parent != nil %> <td><%= locat...

问Rails无错误--有什么方法可以阻止它们吗？
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