Ruby on Rails:提供vs content_for [英] Ruby on Rails: provide vs content_for

问题描述

我今天遇到了提供"视图助手功能.通过查看其手册，我仍然对它与"content_for"的区别感到困惑.

I came across the view helper function "provide" today. By looking into its manual I am still confused on how it is different from "content_for".

提供(名称，内容=无，& block)

provide(name, content = nil, &block)

与content_for相同，但与流式传输一起使用时会直接刷新 回到布局.换句话说，如果您要串联多个 渲染给定模板时，将其复制到相同的缓冲区，您应该 使用content_for，如果不使用，则使用Provide告知布局停止 寻找更多内容.

The same as content_for but when used with streaming flushes straight back to the layout. In other words, if you want to concatenate several times to the same buffer when rendering a given template, you should use content_for, if not, use provide to tell the layout to stop looking for more contents.

问题1:对我来说，这很抽象-有人可以举一个示范性的例子来充实它吗?

Question 1: this is quite abstract to me - could anyone flesh it out by giving a demonstrative example?

问题2:使用资产管道，效果更好，为什么呢?

Question 2: working with asset pipeline, which performs better and why?

谢谢！

推荐答案

首先，什么是流媒体?您为什么要使用它?

流式传输是自上而下(从里到外)呈现页面的另一种方法.默认渲染行为是由内而外的.必须在您的控制器中启用流式传输:

Streaming is alternate method of rendering pages top-down (outside-in). The default rendering behavior is inside-out. Streaming must be enabled in your controller:

class MyController
  def action
    render stream: true # Streaming enabled
  end
end

根据文档:

对于轻量级动作，流媒体可能被认为是过大的 如新建或修改.流媒体的真正好处在于价格昂贵 例如，对数据库执行大量查询的操作.

Streaming may be considered to be overkill for lightweight actions like new or edit. The real benefit of streaming is on expensive actions that, for example, do a lot of queries on the database.

因此，如果您不使用流式传输，还有区别吗?

是的

区别在于模板可以通过多次调用content_for来定义多个内容块.这样做将串联块并将其传递到布局:

The difference is a template can define multiple content blocks by calling content_for multiple times. Doing so will concatenate the blocks and pass that to the layout:

# layout.html.erb
<div class="heading"><%= yield :surprise %></div>
<div class="body">
   <p><%= yield %></p>
   <p>But it's not very interesting...</p>
</div>

# template.html.erb
<%= content_for :surprise, "Hello" %>
I've got your content!
<%= content_for :surprise, ", World!" %>

# Generated HTML
<div class="heading">Hello, World!</div>
<div class="body">
   <p>I've got your content!</p>
   <p>But it's not very interesting...</p>
</div>

由于provide 不再继续搜索所提供的模板，因此只有传递给第一个provide调用的块将被发送到模板:

Since provide doesn't continue searching the provided template, only the block passed to the first provide call will be sent to the template:

# layout.html.erb
<div class="heading"><%= yield :title %></div>

# template.html.erb
<%= provide :title, "Foo" %>
<%= provide :title, "bar" %>

# Generated HTML
<div class="heading">Foo</div>

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