One of the most common html elements in a web page is select box. In Rails select and option tag helper method is used to display it .

select and option tag:

<%= select_tag(:city_id, options_for_select[[Bangalore, 1], [Dehradun, 2]]) %>

# <select id="city_id" name="city_id">
#<option value="1">Banglore</option>
#<option value="2">Dehradun</option>
#</select>

In the above example in the controller we can get the chosen city id as params[:city_id].

The select method looks like this:

select_tag(name, option_tags = nil, options = {})

For the above example name is :city_id , option_tags is options_for_select[[Bangalore, 1], [Dehradun, 2]]. options = {} are the optional arguments. They are :

:multiple - When set to true we can select more than one option.
:disabled - When set to true the select box will be disabled in the web page.
:include_blank - When set to true an empty option will be created.
:prompt - When a string is passed to this option it is displayed as option without any value in the web page.

Others ways of displaying select boxes are:

Select box for model specific form:

select method is used in model specific form for displaying select boxes. Example:

    <%= select(:location, :city_id, [[Bangalore, 1], [Dehradun, 2]]) %>

Please follow this tutorial Rails:Populating Select boxes with model data for details.

Option Tags from a Collection of Arbitrary Objects:

In the above example we have given static values of option tag , but what to do when we have dynamic collection for option tags then we will use options_from_collection_for_select

Example:

<%= select_tag(:city_id,  options_from_collection_for_select(@city, "id", "name")) %>