Rails Partial Templates

What is a Partial Template?

A partial template is really just like any other template but can take parameters. These can also be called ‘partials’.

If you pass in an instance of one model, it will be rendered once; If you pass into it a collection of records of model instances, it will be rendered multiple times.

A partial template can be called/rendered from a controller or another template. Also partial templates can call/render other partial templates.

Why use Partial Templates?

If you are doing too much in your regular non-partial template, move it to a Partial Template, also to keep your code DRY.

For example, in your regular non-partial template, for new and edit, there is usually some duplication. Move that duplicated code into a partial template.

Passing One Object to a Partial

Rails will detect that only one record is passed to the partial _game.html.erb.

In index.html.erb for example:

<% title "Game" %>
<%= render :partial => @game %>

OR:

<% title "Game" %>
<%= render :partial => 'game', :object => @game %>

In the _game.html.erb partial, for example:

<%= game.name %>
<%= game.type %>

Passing Multiple Objects (a Collection) to a Partial

Rails will detect that multiple records are passed to the partial _game.html.erb.

In index.html.erb for example:

<% title "Games" %>
<%= render :partial => @games %>

OR:

<% title "Games" %>
<%= render :partial => 'game', :collection => @games %>

In the _game.html.erb partial, for example:

<%= game.name %>
<%= game.type %>

Rendering Partial Template of a Different View

Sometimes you want to render a partial template that’s not in the default location. For instance, this partial views/stores/_fields.html.erb is associated with the ‘stores’ view not ‘products’ but it can still be rendered.

Imagine the following code is located in views/products/new.html.erb and you want to display two separate forms after each other both on the same page. Each store has many products. :locals allows you to pass variables to your partial template.

<% form_for(@store) do |f| %>
  <%= render :partial => '/stores/fields', :locals => { :f => f } %>
    <%= f.submit "Create" %>
<% end %>

<% form_for(@product) do |f| %>
  <%= render :partial => '/products/fields', :locals => { :f => f } %>
    <%= f.submit "Create" %>
<% end %>

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