Partials

Location

The view partial files are located in the app/views/partials directory.

Convention

Despite views, partials and layouts having separate directories, it may sometimes get confusing having to deal with all three when working on your application.

Following Rails convention, file names for partials should ideally begin with an underscore.

Typical example pattern

Suppose we have a portfolio website where projects are displayed on the projects page.

The projects page will be loaded with a layout, and so is not a full view itself. One typical approach would be:

app/views/projects.erb

<p>Here is a selection of a few projects that I have either:</p>
<ul>
    <li>Created myself</li>
    <li>Been an essential part of the development team</li>
</ul>
​
<div id="projects">
    <% @projects.each do |project| %>
    <div class="project">
        <h2><%= project[:title] %></h2>
        <p><%= project[:description] %></p>
        <%= link_to "Repository link", project[:link] %>
        <ul>
        <% project[:languages].each do |lang| %>
            <li><span><%= lang %></span></li>
        <% end %>
        </ul>
    </div>
    <% end %>
</div>

But ideally view files should be clean, easy to read and most importantly, isolated from the logic.

Typically logic should be restricted to controllers, models and helpers (as well as partials where appropriate).

To clean this view file up, we will need a new partial containing all of the erb code necessary for displaying projects (Simply copying the ruby code part from the above view file).

app/views/partials/_projects.erb

<div id="projects">
    <% @projects.each do |project| %>
    <div class="project">
        <h2><%= project[:title] %></h2>
        <p><%= project[:description] %></p>
        <%= link_to "Repository link", project[:link] %>
        <ul>
        <% project[:languages].each do |lang| %>
            <li><span><%= lang %></span></li>
        <% end %>
        </ul>
    </div>
    <% end %>
</div>

We can then clean up our projects.erb file by calling the partial function (which is already defined in Eucalypt) in the view:

app/views/projects.erb

<p>Here is a selection of a few projects that I have either:</p>
<ul>
    <li>Created myself</li>
    <li>Been an essential part of the development team</li>
</ul>
​
<%= partial 'partials/_projects' %>
<!-- Or alternatively -->
<%= partial '_projects' %>

If you have variables that need to be used in the partial, simply pass them as keyword arguments in the partial function:

<%= partial '_projects', count: 10, top_lang: 'Ruby' %>
<!-- Or alternatively -->
<%= partial '_projects', {count: 10, top_lang: 'Ruby'} %>

The variables count and top_lang will then be usable in the partial's ERB file. They are treated as local variables, so just access them by their name.