Selections lists are, in many ways, like radio buttons on a larger scale. Rather than filling a screen with radio buttons, a list lets you hide the options except during that critical time when you’re actually making a selection. Showing radio buttons for over 190 countries would take up a huge amount of screen real estate. Selection lists offer a much more compact but still convenient way for users to make choices.
Rails has a number of helper methods for creating selection lists,
but the simplest place to start is the select
method. In its most basic form, select
takes two arguments: the attribute that
populates it and a set of choices. Choices can be represented in a
number of different ways, from a simple array of strings to a hash or
other more complex set of values.
At the time this was written, this simplest form of select
wasn’t actually documented in the
Rails API docs. If you look at the documentation for a function and it
seems like it’s more complex than you need, it’s sometimes worth
experimenting to see whether a simpler form will work. The docs often
seem to give priority to more complex use cases. (As you become a
guru, you’ll likely be able to look at the Rails source code and
figure it out, but Ruby’s many options make it tricky at
first.)
Using an array of strings, the call to create a selection list might look like:
<p> <b>Country</b><br /> <%= f.select (:country, ['Canada', 'Mexico', 'United Kingdom', 'United States of America'])%> </p>
This generates:
<p> <b>Country</b><br /> <select id="person_country" name="person[country]"><option value="Canada">Canada</option> <option value="Mexico">Mexico</option> <option value="United Kingdom">United Kingdom</option> <option value="United States of America">United States of America</option></select> </p>
When working from a simple list of strings, Rails creates
option
elements whose
value
attributes—the values sent back
to the server—are the same as the content displayed to the user, as
shown in Figure 6-4.
You can be a little more specific about what you want by using a two-dimensional array. The display values come first, and the values that go to the server come second:
<p> <b>Country</b><br /> <%= f.select (:country, [ ['Canada', 'Canada'], ['Mexico', 'Mexico'], ['United Kingdom', 'UK'], ['United States of America', 'USA'] ])%> </p>
This still looks the same as the result in Figure 6-4, but the underlying HTML has changed a bit:
<p> <b>Country</b><br /> <select id="person_country" name="person[country]"><option value="Canada">Canada</option> <option value="Mexico">Mexico</option> <option value="UK"
>United Kingdom</option> <option value="USA"
>United States of America</option></select> </p>
The new value
attributes for
the United Kingdom and United States of America reflect the explicit
choices made in the underlying array.
You can also set a default choice for your selections by adding a
selected
named parameter:
<%= f.select (:country, [ ['Canada', 'Canada'],
['Mexico', 'Mexico'],
['United Kingdom', 'UK'],
['United States of America', 'USA'] ],
:selected => 'USA'
)%>
This generates the same markup, except that the option
element for USA now looks like:
<option value="USA" selected="selected"
>United States of America</option>
You can also use select
with a
hash, instead of specifying the array. Example 6-5 shows how this
looks much like it did for the radio buttons in Example 6-4.
Example 6-5. Creating a sorted selection list from a hash
<% nations = { 'United States of America' => 'USA', 'Canada' => 'Canada', 'Mexico' => 'Mexico', 'United Kingdom' => 'UK' }%> <p> <b>Country</b><br /> <% list = nations.sort %> <%= f.select :country, list %> </p>
Rails also offers a number of specific selection fields, including
one for countries (country_select
)
and one for time zones (time_zone_select
). Additionally, if you decide that you want to get really
fancy, you can create multilevel selection lists with option_groups_from_collection_for_select
. You
can also create selection lists that let users choose multiple values by
setting the :multiple
option to true
.
The country_select
method has
proven a bit controversial, mostly because of the base list of countries
it uses. Future versions of Rails may be moving it out of the main
framework and into a plug-in.