When displaying individual records, the current show.rhtml template shows an ugly blank where a field has no set value. Instead, it may be better to show a default message where a record has a blank field, e.g. "not specified". We will potentially need this functionality in multiple views, so it makes sense to add the helper to app/helpers/application_helper.rb:

module ApplicationHelper
# Display a default message for empty fields.
#
# +field_value+ is the value to process.
def d(field_value=nil)
if field_value.blank?
return content_tag('em', 'not specified')
else
return field_value
end
end
end

The d method (helper) defined here is passed a field value, which is interrogated by the Rails convenience method blank?; blank? returns true if the value is empty or nil. If no argument is passed, the value nil is assigned to field_value by default (the parameter field_value=nil in the method signature specifies the default). If the field value is blank, the helper supplies a default empty field message inside an<em> element, via the content_tag helper: this takes a string representing an HTML tag as the first argument, and the content to put inside the tag as its second argument; optionally, you can pass extra :attribute => value pairs to add to the HTML element.

This method can be called wherever a field could be blank. For example, we can rewrite app/views/people/show.rhtml using it (highlighted lines below):

<h1><%= @page_title %></h1>
<p><strong>Job title:</strong> <%=d @person.job_title %></p>

<p><strong>Email address:</strong> <%= mail_to @person.email %></p>
<p><strong>Telephone:</strong> <%=d @person.telephone %></p>
<p><strong>Mobile phone:</strong> <%=d @person.mobile_phone %></p>
<p><strong>Date of birth:</strong> <%=d @person.date_of_birth %></p>

<p><strong>Gender:</strong> <%= @person.gender %></p>
<p><strong>Keywords:</strong> <%=d @person.keywords %></p>
<p><strong>Notes:</strong><br/><%=d @person.notes %></p>

However, for fields that are never empty (because we made sure they had a value when performing validation), we don't need to use the d function.

The display for a person's date of birth defaults to the international standard date notation (YYYY-MM-DD, e.g. "1968-01-08"). However, this is alien to most people: it would make more sense to show a "humanized" version of the date instead (e.g. "8th January 1968"). We could first add a generic date formatting method to the application_helper.rb file to do this:

module ApplicationHelper
...
# Display date in human-readable format, e.g. "8th January 1968".
#
# Returns +nil+ if +date_to_format+ is blank.
def human_date(date_to_format)
if date_to_format.blank?
out = nil
else
# Get the day part of the date with
# the "ordinal suffix" (th, rd, nd) appended
day = date_to_format.day.ordinalize
# strftime accepts a formatting string, which specifies
# which parts of the date to include in the output string
out = date_to_format.strftime("#{day} %B %Y")
end
out
end
end

The strftime method used in the human_date method is very useful for formatting Date and DateTime objects. It accepts a format string, much like PHP's strftime function, containing placeholders for elements of the date and/or time, marked with a preceding "%" character. Here are the placeholders you can use with the Ruby version of strftime; the examples, all use 6th December 2006 at 9:30 a.m. as the date being formatted:

"Zero-padded" means that a single leading zero is added to the representation of the time part if its value is less than 10.

Here are a few more examples of format strings for strftime, using some of these placeholders:

We can now modify app/views/people/show.rhtml to use our new human_date method:

<p><strong>Date of birth:</strong>
<%=d human_date(@person.date_of_birth) %></p>

There are several repeated lines in the template, which show parts of the address (plus a<br /> element), but only if they have a value, e.g:

<%= address.street_2 + tag('br') unless address.street_2.blank? -%>

This is a good case where an application-level helper can reduce the repetition in a template:

module ApplicationHelper
...
# Display +field_value+ followed by a <br> element,
# but only if +field_value+ is set; otherwise return nil.
def field_with_break(field_value)
unless field_value.blank?
return field_value + tag('br')
else
return nil
end
end
end

We can now reduce the address part of the template to:

<p><strong>Address:</strong><br/>
<% address = @person.address -%>
<% if address -%>
<%= address.street_1 %><br/>
<%= field_with_break address.street_2 -%>
<%= field_with_break address.street_3 -%>
<%= field_with_break address.county -%>
<%= field_with_break address.city -%>
<%= address.post_code %>
<% else -%>
<%=d nil %>
<% end -%>
</p>

The show.rhtml template is specific to a person: it shows their details, including their home address. However, companies can also have addresses: so we will need to include some code to render a company's address in app/views/companies/index.rhtml (we've avoided this so far).

One option would be to add a block of address-rendering code to app/views/addresses/index.rhtml, to show the address for each company; this would be similar to the code we already have in app/views/people/show.rhtml. But this would mean repeating ourselves, as we would have identical blocks of code in multiple locations.

In addition to adding repetition, we are already breaking Rails conventions by rendering addresses from inside views for PeopleController. Typically, the templates for a model are stored in a folder specific to the corresponding controller; but here, the RHTML code for rendering an Address is tied into the template for the Person model. But, at the same time, we don't want to show an address in its own full-page template: we only want to show it in conjunction with a person or company. So adding a full template for displaying an address inside a layout is unnecessary.

Rails provides a solution for this situation: partial templates (or partials for short). A partial is used to generate a page fragment (typically RHTML), which can be used inside other templates. They can be called from inside other RHTML files, or even rendered directly from inside a controller (in lieu of a full-page template), to produce a "fragment" of output.

By convention, Rails partials are included in the views directory for the controller. In our case, a partial for addresses goes in app/views/addresses. To distinguish partials from full-page templates, an underscore is prepended to the name of the partial: for example, the partial to show an address would intuitively be called _show.rhtml. Our partial should therefore go in the file app/views/addresses/_show.rhtml; the content can be cut and pasted from the show.rhtml file for people (app/views/people/show.rhtml), and looks like this:

<% if address -%>
<%= address.street_1 %><br/>
<%= field_with_break address.street_2 -%>
<%= field_with_break address.street_3 -%>
<%= field_with_break address.city -%>
<%= field_with_break address.county -%>
<%= address.post_code %>
<% else -%>
<%= d %>
<% end -%>

The main difference between the original we copied and this code is that references to the @person variable have been removed. Instead, a local variable called address is referenced. Provided this variable is passed to the partial when it is called from a controller or view, the partial can be used inside any other template.

Another difference is that paragraph tags have been removed from the partial. This means the output can be used either inside paragraphs (e.g. when showing a person) or inside table cells (e.g. in the companies list).

To render the partial inside another template, call it using the render method, e.g. in app/views/people/show.rhtml:

...
<p><strong>Notes:</strong><br/><%=d @person.notes %></p>
<p><strong>Address:</strong></p>
<p><%= render :partial => 'addresses/show',
:locals => {:address => @person.address} %></p>

Two things to note here are:

We can also reuse this partial inside app/views/companies/index.rhtml:

<% for company in @companies -%>
<tr>
<td>
<%= link_to company.name, { :action => 'show', :id => company.id },
{ :title => "Show details for this company" } %>
</td>
<td><%= company.telephone %></td>
<td><%= company.fax %></td>
<td><%= link_to(company.website, company.website) %></td>
<td><%= render :partial => 'addresses/show',
:locals => {:address => company.address} %></td>

</tr>
<% end -%>