Rails what does this "yield" do? - ruby-on-rails

What does the yield do in this snippet?
<body data-spy="scroll" data-target=".sidebar">
<!-- Your timezone is <%= Time.zone %> -->
<!-- <%= "Ruby Version is #{RUBY_VERSION}" if Rails.env =~ /test|development/ %> -->
<%= render partial:'shared/account_status' %>
<%= render partial:"shared/session_timeout" %>
<div class="container">
<%= render partial:"shared/branding" %>
<%= render partial:"shared/nav", locals:{icons:icons, actionable_urls:actionable_urls, top_level_items:MenuItem.top_level_items_with_access_rights_for_user(current_user).sort{|a, b| a.sequence <=> b.sequence}, current_item:current_navigation_item} %>
<div style="clear:both"></div>
<div id="content">
<%= render partial:"shared/flash", object:flash %>
<%= yield %>
</div>
</div>
<%= render partial:"shared/ldap_user_menu" if signed_in_as_ldap_user? %>
</body>
SOLUTION
see #Christian_Rolle 's answer below

The reserved Ruby key word yield is for processing closures (like a Proc or lamda). That said it is some kind of placeholder for processing some logic.
In Ruby on Rails view templating it is used for merging in partials. In the case of a layout file like the application.html.erb it merges in controller response templates like index.html.erb or show.html.erb.
Think of it as a placeholder for your controller response HTML in a global layout environment.
Read more at: Understanding yield
or about Ruby closures:
Do the Proc! ... a Ruby closure and
Have a lambda! ... a Ruby closure

okay ... lets talk about it in easy way , yield is like a placeholder or like a container . And while you make different parts of view and want to show it on any specific layout file , then you can just call that part on the yield section . And this is all it does .

Related

Rendering multiple erb in rails

I have layour/application.html.erb with all required headers and nav bar. I have yield only in body section.
My dashboard.html.erb is hope page which is set of graphs. I want to write each graph in a different erb and its own javascript. So I sketched up,
dashboard.html.erb as:
<div> hello </div>
<%= render 'hierarchical' %>
and
dashboard/_hierarchical.html.erb as:
<head>
<%= javascript_include_tag "_hierarchical.js" %>
</head>
<div id="chart">
test something
</div>
I think I need to read more about ruby which I will but need quick help on this so that I can have my sample demo app running asap. Thanks for your help!
I was doing it wrong without using :partial symbol.
This code worked
<div> hello </div>
<%= render :partial => 'hierarchical' %>

Rails: Correct way of making exception of "Yield" by using "Content_for"?

I have a Rails app, in which I fit my entire website into a 980width container with the following code in my 'application.html.erb' file:
<div class="container_980 white shadow-horizontal">
<div class="container">
<%= render 'layouts/flashes' %>
<%= yield %>
</div>
</div>
Now, I want to make 2 file exceptions for fitting the content within the container. I want the index page and another page to expand across the entire page, so I need to get those two pages outside of the common 'yield' set above.
I tried doing so with:
<% if current_page?(root_url) %>
<%= yield :index %>
<% elsif current_page?(:controller => "tracks", :action => "show", :id => params[:id])) %>
<%= yield :show_track %>
<% else %>
<div class="container_980 white shadow-horizontal">
<div class="container">
<%= render 'layouts/flashes' %>
<%= yield %>
</div>
</div>
and
<% content_for :show_track do %>
blah blah blah
<% do %>
THE PROBLEM: The show_track page doesn't load. I did some searching, and it seems like the above method should work, but it's not, and I was wondering if I needed to do something else as the "show" page was made through scaffoldaing(RESTful).
Is there a better way to take out the 2 pages from the container than using if..else conditions?
Is there a better way to take out the 2 pages from the container than using if..else conditions?
This is subjective, but I would use nested layouts, then define the layouts for each page type in the controller.
First your basic top level layout. I'm calling it "application", the default, but you could call it whatever. Note how if there's content_for? :application it will yield it, otherwise it will just yield. This is key to the setup. All nested layouts should follow a similar pattern; in this way they can render further nested child layouts, or be used as layouts themselves.
<!-- layouts/application.html.erb -->
<html>
<body>
<%= content_for?(:application) ? yield(:application) : yield %>
</body>
</html>
Then for the container, you'd define layout which can be nested inside "application", this one setting up your container HTML and rendering content inside.
<!-- layouts/container.html.erb -->
<%= content_for :application do %>
<div class="container_980 white shadow-horizontal">
<div class="container">
<%= render 'layouts/flashes' %>
<%= content_for?(:container) ? yield(:container) : yield %>
</div>
</div>
<% end %>
<%= render :file => "layouts/application" %>
Then just move your conditional logic to the controller, like:
layout :determine_layout
protected
function determine_layout
# pseudocode here, you get it
(index or tracks) ? "application" : "container"
end
You could stop there. Continue to see how you might further nest layouts.
However you could go further, and use the nested layout setup to nest arbitrary numbers of different layouts. Say, for example, that tracks had another content block you needed to fill. You could define another nested layout, like:
<!-- layouts/tracks.html.erb -->
<%= content_for :some_other_block do %>
// stuff that should be in some other block
<% end %>
<%= content_for :container do %>
// stuff that should be in the container
<% end %>
<%= render :file => "layouts/container" %>
Then in your controller, you'd change your determine_layout to set the "tracks" layout for tracks, e.g.:
function determine_layout
# pseudocode here, you get it
if index
"application"
elsif tracks
"tracks"
else
"container"
end
end

Rails: Using Yield, Calling Multiple View Pages

Problem: How Do You Render Multiple View Pages From Different Controllers?
In my views/layouts/application.html.erb, I call views/posts/index.html.erb with the yield method.
<div class='span10'>
<%= yield %>
</div>
On top of it, I wanted to call views/good_posts/index.html.erb with yield. So in that particular index file, I wrap around all the code with content_for method.
<%= content_for :good_post do %> all my content in good_post/index.html.erb <% end %>
I go back to application.html.erb, I tried to call the index file of good_post with yield method.
<div class='span10'>
<%= yield :good_post %>
</div>
<div class='span10'>
<%= yield %>
</div>
I thought this would result in good_post/index to be rendered on top of post/index, but it did not work; only post/index was correctly rendered as before. Could someone explain why this is, and tell me the correct way to approach this problem? I appreciate your help!
You should, as #cdesrosiers said, rename the index.html.erb file in good_posts to _index.html.erb. Then you can render this view in your application like this:
<div class='span10'>
<%= render 'good_posts/index' %>
<%= yield :good_post %>
</div>
<div class='span10'>
<%= yield %>
</div>
Personally, I would change the index.html.erb file in good_posts folder to _good_posts.html.erb file in app/views/posts folder. Your code will have better meaning, and you can know where to find it after, because it relates to posts. So, if you change this, use this code:
<div class='span10'>
<%= render 'posts/good_posts' %=
<%= yield :good_post %>
</div>
<div class='span10'>
<%= yield %>
</div>
Another you should change is content_for :good_post -> content_for :good_posts , because good posts maybe have many posts, so you should use post in pluralize.

how to extend child template to parent in rails

I am new to rails. I am having difficulty in understanding template inheritance. Earlier I have worked in django and seen template inheritence there. There I saw child is told about parent using "extends" command. Can anyone explain how it works here. I have gone through guidelines of ruby but it was not clear.
Thanks
It's quite simple to do in Rails.
You simply tell the template you are currently rendering to render another template.
For example layouts/application.html.erb contains something like this:
<% content_for :navigation do %>
<nav>...</nav>
<% end %>
<% content_for :content do %>
<%= yield %>
<% end %>
<%= render :template => 'layouts/main_application' %>
The important part is the render :template part that then delegates this template to also render the layouts/main_application.html.erb that in my case looks something like this:
<header>
...
</header>
<body>
<%= yield :nav %>
<%= content_for?(:content) ? yield(:content) : yield %>
</body>
What I am doing here is having a main template that does not contain the navigation (for things like login etc) and the application.html.erb adds that navigation to the :nav content placeholder.

Rails Views: How do you pass a variable to a partial layout?

In one of my views I apply a layout to a block of code:
# In app/views/sessions/new.html.erb
<% render :layout => 'home/shadow_box' do %>
#... code for sign in form here
<% end %>
The layout is a div that has png shadows on all four sides.
Since I use this layout all over my site, I want to pass a variable to the layout that specifies the width of the shadowed div. I tried using content for in the code block:
# In app/views/sessions/new.html.erb
<% render :layout => 'home/shadow_box' do %>
<% content_for :box_width %>640<% end %>
#... code for sign in form here
<% end %>
# In app/views/home/_shadow_box.html.erb
<div class="shadow-one" style="width:<%= yield :box_width %>;">
<div class="corner-a"></div>
<div class="corner-b"></div>
<div class="shadow-two">
<div class="shadow-three">
<div class="shadow-four">
<%= yield %>
</div>
</div>
</div>
</div>
This didn't work and instead resulted in a double render of the entire code block.
What's the best way to tackle this problem?
Figured it out.
From the API: "You can also yield multiple times in one layout and use block arguments to differentiate the sections."
Solution:
# In app/views/sessions/new.html.erb
<% render :layout => 'home/shadow_box' do | section | %>
<%- case section when :box_width -%>
#width goes here. I.e., 640px
<%- when :content -%>
#code block goes here
<% end -%>
<% end %>
#In app/views/home/_shadow_box.html.erb
<div class="shadow-one" style="width:<%= yield :box_width %>;">
<div class="corner-a"></div>
<div class="corner-b"></div>
<div class="shadow-two">
<div class="shadow-three">
<div class="shadow-four">
<%= yield :content %>
</div>
</div>
</div>
</div>
First you need to know the difference between layouts and partials. Partials are generally from the view but can also be used from the controller if you are using ajax. Layouts are almost always used in the controller.
First create a file in a shared folder such as application/ and in this folder put a file call it whatever you want but it will contain the material that you want to include all over your site. Then when you pass a variable to a partial it's called in the partial as a local variable. Also with partials you don't need to say render :partial => you just put render 'application/some_file'
So from the view you want this:
<%= render 'application/your_file', :div_size => '600' %>
And then from the partial in the folder such as application/your_file.html.erb do this:
<div style="width:<%= div_width %>px;">
content
</div>

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