Rails select helpers unraveled

I have observed that there is lot of confusions regarding select box or collection helpers in Rails. Rails API documentation is not very clear about which helper to use in which situation. In this blog, I have tried to simplify the select box helper APIs by giving examples and various scenarios. Majorily, there are two helpers which are helpful in creating a select boxes in Rails select & collection_select. Though other helpers in the documentation are still useful but these are adequate to achieve anything.

The syntax for the select is

select(object, method, choices, options = {}, html_options = {})

Let us start with the very basic select box:-

<%=select “post”, “person_id”, [“Person1”, “Person2”, “Person3”]%>

Output:

<select id="post_person_id" name="post[person_id]">

<option value="Person1">Person1</option>

<option value="Person2">Person2</option>

<option value="Person3">Person3</option>

</select>

 

Options for this Helper

 Include the blank option automatically

<%=select “post”, “person_id”, [“Person1”, “Person2”, “Person3”],  {:include_blank => true}%>

Output:

<select id="post_person_id" name="post[person_id]">

<option value=" "> </option>

…

</select>

 <%=select “post”, “person_id”, [“Person1”, “Person2”, “Person3”],  {:include_blank => “Please select”}%>

Output:

<select id="post_person_id" name="post[person_id]">

<option value=" ">Please select </option>

…

</select>

 

You can disable the options you want

<%=select “post”, “person_id”, [“Person1”, “Person2”, “Person3”],  {:include_blank => “Please select”, :disabled => [“Person1”,  “Person2”]}%>

 

Override the selected value

<%=select “post”, “person_id”, [“Person1”, “Person2”, “Person3”],  {:include_blank => “Please select”, :selected => “Person1”}%>

Output:

<select id="post_person_id" name="post[person_id]">

<option value="Person1" selected=”selected”>Person1</option>

<option value="Person2">Person2</option>

<option value="Person3">Person3</option>

</select>

 

HTML Options in the helper

Add HTML attributes

<%=select “post”, “person_id”, [“Person1”, “Person2”, “Person3”],  {:include_blank => “Please select”, :selected => “Person1”}, {:class => “html_class” }%>

Output:

<select id="post_person_id" name="post[person_id]" class=”html_class”>

<option value="Person1" selected=”selected”>Person1</option>

<option value="Person2">Person2</option>

<option value="Person3">Person3</option>

</select>

Other methods to specify Choices in the helper

<%=select “post”, “person_id”, {“1” => “Person1”, “2” => “Person2”, “3” => “Person3”}%>

Or

<%=select “post”, “person_id”, [ [“Person1“,  “1”], [“Person2”, “2”],[“Person3”, “3”]]%>

In case you have collection of objects

<%=select “post”, “person_id”,  Person.all.collect{ |p| [p.name, p.id]}%>

The collection_select helper is also very useful if you have collection of objects. For the above select it can written like this. It has a syntax like:-

collection_select(object, method, collection, value_method, text_method, options = {}, html_options = {})

So,

<%=collection_select “post”, “person_id”, Person.all,  :id,  :name%>

Grouped Select Boxes

In case you want to have grouped collection/select box there are two helpers which can help you create it grouped_collection_select and grouped_options_for_select

grouped_options _for_select is used along with select to group related options together.

<%

grouped_options = {“North America” => [[“United States”, “US”], “Canada”], “Europe” => [“Denmark”, “Germany”, “France”]}

%>

<%=select “post”, “person_id”, grouped_options_for_select(grouped_options), {:include_blank => “Please Select”%>

There are more options like :divider, :prompt which you can pass on to the grouped_options_for_select, whose details can be found here http://api.rubyonrails.org

 

Output:

<select id="post_person_id" name="post[person_id]">

<option value="">Please Select</option>

<optgroup label="Europe"><option value="Denmark">Denmark</option>

<option value="Germany">Germany</option>

<option value="France">France</option></optgroup>

<optgroup label="North Americal"><option value="US">United States</option>

<option value="Canada">Canada</option></optgroup>

</select>

grouped_collection_select helper is bit tricky to use and has syntax like this

grouped_collection_select(object, method, collection, group_method, group_label_method, option_key_method, option_value_method, options = {}, html_options = {})

This is what rails documentation has to say

Returns <select>, <optgroup> and <option> tags for the collection of existing return values of method for object‘s class. The value returned from calling methodon the instance object will be selected. If calling method returns nil, no selection is made without including :prompt or :include_blank in the options hash.

Parameters:

·         object - The instance of the class to be used for the select tag

·         method - The attribute of object corresponding to the select tag

·         collection - An array of objects representing the <optgroup> tags.

·         group_method - The name of a method which, when called on a member of collection, returns an array of child objects representing the <option> tags.

·         group_label_method - The name of a method which, when called on a member of collection, returns a string to be used as the label attribute for its<optgroup> tag.

·         option_key_method - The name of a method which, when called on a child object of a member of collection, returns a value to be used as the valueattribute for its <option> tag.

·         option_value_method - The name of a method which, when called on a child object of a member of collection, returns a value to be used as the contents of its <option> tag.

Example object structure for use with this method:

class Continent < ActiveRecord::Base

  has_many :countries

  # attribs: id, name

end

 

class Country < ActiveRecord::Base

  belongs_to :continent

  # attribs: id, name, continent_id

end

 

class City < ActiveRecord::Base

  belongs_to :country

  # attribs: id, name, country_id

end

Sample usage:

grouped_collection_select(:city, :country_id, @continents, :countries, :name, :id, :name)

Possible output:

<select name="city[country_id]">

  <optgroup label="Africa">

    <option value="1">South Africa</option>

    <option value="3">Somalia</option>

  </optgroup>

  <optgroup label="Europe">

    <option value="7" selected="selected">Denmark</option>

    <option value="2">Ireland</option>

  </optgroup>

</select>

Here, I have presented the form helpers which are not bonded to any model. For forms which are bound to models use them as

<%=form_for @person%>

<%=f.select :person_id ….%>

<%=f.collection_select :person_id ….%>

<%end%>

That is all from my side. Here I have tried to cover every possible scenario to create select boxes using rails helpers. Hope this will help rails developer find the best suited helper for them.

In case you have any questions/suggestions, you can connect to me at developer.vineet@gmail.com