Ruby-on-rails 是否有任何 Rails 函数来检查部分是否存在？
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Is there any Rails function to check if a partial exists?
提问by Daniel Cukier
When I render a partial which does not exists, I get an Exception. I'd like to check if a partial exists before rendering it and in case it doesn't exist, I'll render something else. I did the following code in my .erb file, but I think there should be a better way to do this:
当我渲染一个不存在的部分时，我得到一个异常。我想在渲染之前检查部分是否存在，如果它不存在，我将渲染其他内容。我在我的 .erb 文件中做了以下代码，但我认为应该有更好的方法来做到这一点：
<% begin %>
<%= render :partial => "#{dynamic_partial}" %>
<% rescue ActionView::MissingTemplate %>
Can't show this data!
<% end %>
回答by Rein
Currently, I'm using the following in my Rails 3/3.1 projects:
目前，我在 Rails 3/3.1 项目中使用以下内容：
lookup_context.find_all('posts/_form').any?
The advantage over other solutions I've seen is that this will look in all view paths instead of just your rails root. This is important to me as I have a lot of rails engines.
与我见过的其他解决方案相比，它的优势在于，这将查看所有视图路径，而不仅仅是您的 Rails 根。这对我很重要，因为我有很多 Rails 引擎。
This also works in Rails 4.
这也适用于 Rails 4。
回答by Jeff
I was struggling with this too. This is the method I ended up using:
我也为此苦苦挣扎。这是我最终使用的方法：
<%= render :partial => "#{dynamic_partial}" rescue nil %>
Basically, if the partial doesn't exist, do nothing. Did you want to print something if the partial is missing, though?
基本上，如果部分不存在，则什么都不做。但是，如果缺少部分内容，您是否想打印一些东西？
Edit 1:Oh, I fail at reading comprehension. You did say that you wanted to render something else. In that case, how about this?
编辑1：哦，我阅读理解失败。你确实说过你想渲染别的东西。既然如此，那怎么办？
<%= render :partial => "#{dynamic_partial}" rescue render :partial => 'partial_that_actually_exists' %>
or
或者
<%= render :partial => "#{dynamic_partial}" rescue "Can't show this data!" %>
Edit 2:
编辑2：
Alternative: Checking for existence of the partial file:
替代方法：检查部分文件是否存在：
<%= render :partial => "#{dynamic_partial}" if File.exists?(Rails.root.join("app", "views", params[:controller], "_#{dynamic_partial}.html.erb")) %>
回答by Luke Imhoff
From inside a view, template_exists? works, but the calling convention doesn't work with the single partial name string, instead it takes template_exists?(name, prefix, partial)
从视图内部来看，template_exists？有效，但调用约定不适用于单个部分名称字符串，而是采用 template_exists?(name, prefix, partial)
To check for partial on path: app/views/posts/_form.html.slim
检查路径上的部分：app/views/posts/_form.html.slim
Use:
用：
lookup_context.template_exists?("form", "posts", true)
回答by Flackou
In Rails 3.2.13, if you're in a controller, you can use this :
在 Rails 3.2.13 中，如果你在控制器中，你可以使用这个：
template_exists?("#{dynamic_partial}", _prefixes, true)
template_exists?is delegated to lookupcontext, as you can see in AbstractController::ViewPaths
template_exists?被委托给lookupcontext，正如您在AbstractController::ViewPaths
_prefixesgives the context of the controller's inheritance chain.
_prefixes给出控制器继承链的上下文。
truebecause you're looking for a partial (you can omit this argument if you want a regular template).
true因为你正在寻找一个部分（如果你想要一个常规模板，你可以省略这个参数）。
回答by afxjzs
I know this has been answered and is a million years old, but here's how i ended up fixing this for me...
我知道这已经得到了回答并且已经有一百万年的历史了，但这就是我最终为我解决这个问题的方式......
Rails 4.2
导轨 4.2
First, i put this in my application_helper.rb
首先，我把它放在我的 application_helper.rb
def render_if_exists(path_to_partial)
render path_to_partial if lookup_context.find_all(path_to_partial,[],true).any?
end
and now instead of calling
现在而不是打电话
<%= render "#{dynamic_path}" if lookup_context.find_all("#{dynamic_path}",[],true).any? %>
<%= render "#{dynamic_path}" if lookup_context.find_all("#{dynamic_path}",[],true).any? %>
i just call <%= render_if_exists "#{dynamic_path}" %>
我只是打电话 <%= render_if_exists "#{dynamic_path}" %>
hope that helps. (haven't tried in rails3)
希望有帮助。（没在 rails3 中试过）
回答by br3nt
I have used this paradigm on many occasions with great success:
我在很多场合都使用过这个范式，并取得了巨大的成功：
<%=
begin
render partial: "#{dynamic_partial}"
rescue ActionView::MissingTemplate
# handle the specific case of the partial being missing
rescue
# handle any other exception raised while rendering the partial
end
%>
The benefit of the code above is that we can handle tow specific cases:
上面代码的好处是我们可以处理两种特定情况：
- The partial is indeed missing
- The partial exists, but it threw an error for some reason
- 部分确实缺失
- 部分存在，但由于某种原因引发了错误
If we just use the code <%= render :partial => "#{dynamic_partial}" rescue nil %>or some derivative, the partial may exist but raise an exception which will be silently eaten and become a source of pain to debug.
如果我们只是使用代码<%= render :partial => "#{dynamic_partial}" rescue nil %>或一些派生类，部分可能存在但会引发异常，该异常将被默默吃掉并成为调试的痛苦之源。
回答by Andrey
What about your own helper:
你自己的帮手呢：
def render_if_exists(path, *args)
render path, *args
rescue ActionView::MissingTemplate
nil
end
