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What is the difference between render and yield in Rails

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自闭症患者 2021-02-13 11:00

Can someone explain the difference between \"<%= render %>\" and \"<%= yield %> with <% content_for :partial do %>/

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  • 时光取名叫无心
    2021-02-13 11:31

    When your controller method exits, it renders the associated file. So the edit controller renders edit.html.erb. It uses the specified layout or application.html.erb if none is specified.

    Within your layout file, when you call yield it will fill in the information from your render. If you call yield with a parameter, it will look for a content_for section in your render file matching that parameter. I'm not completely sure, but I don't think you can call yield from outside of your layout file, and I don't think it will fill in any information except that found in your render file.

    Anywhere in your layout file or your rendered file, you can render a partial by calling render with the partial name minus the underscore.

    I hope that helps.

    Edit to answer question in comment:

    yield and render perform similar functions however yield only looks in the render file whereas render specifies which file to render. Also, render outputs the entire file, but yield with a parameter can output just a subsection of the file.

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  • 不思量自难忘°
    2021-02-13 11:39

    yield

    Ruby code (Proc class) and takes your block and does what it is supposed to do with it. Yield is also fast compared with other Ruby based ways of doing the same thing. I'd assume (and I only) use it in the layouts because it's quick and I mindlessly do what's normal in Rails. yield is also used to pass content to a specific spot in your layout. I often have <%= yield :head %> in the head, just above the head tag, so that I can pass random weirdness that sometimes comes up.

    Common Uses:

    • Mostly just used in layouts
    • (if you are fancy/inclined to do so in a Model) as a true Ruby Proc statement.

    render

    Rails code that you pass arguments to that, as the docs say, "Renders the content that will be returned to the browser as the response body". partials, actions, text, files...etc.

    Common Uses:

    Used in both views and the controller.

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  • 我寻月下人不归
    2021-02-13 11:46

    First of all, yield is ruby, render is rails. Usually one uses a common layout for the application whose inner content changes according to action/context. The problem usually lies in defining where our layout ends and context-specific template begins. Take, for instance, the HTML title tag. Let's say you have an application called Cities. In most cases, you want your page title to be "Cities" all the time. But, if you're for instance, inside Amsterdam page, then you would like the have "Amsterdam" as your page title.

    # application.html.erb
<html>
  <head>
    <%= content_for?(:page_title) ? yield(:page_title) : "Cities" %>
    ......

# city/index.html.erb
<% content_for :page_title do %>
  <%= @city.name %> 
<% end %>

<div class="bla"...

    Within Rails you usually define your application title in your application layout. One strategy for changing the page title would be to use content_for in the specific cities template and change accordingly.

    Render, on the other hand, accomplishes different rendering strategies. Straight. When you call render, it renders. content_for/yield doesn't render automatically, it is stored somewhere and then fills up the missing spots in the due places. So, you can think of it as more as a "store/search/replace" in comparison to render, which just plain renders.

    Good rule of thumb to use one over the other is: if the template you are writing needs to present different information per context, strongly consider using content_for.

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