Drop down select list

One of the first thing I encounter was to find a way how to associate tables. The simples association could be for example this:
You have several books represented by the Book object and stored in the books table in the DB. This books have a status that could be Available, Borrowed or Missing. Now, in order to represent that in Rails you need to create those two classes and associate them so in the View you can select from a drop down list the correct status.

Let's start creating a rails project, open your console and type:

rails new library
cd library

create the objects

rails g scaffold Book name:string status_id:integer


rails g scaffold Status name:string

create the tables for each object

rake db:migrate

In the models you have to add the association for each class.

For book:

class Book < ActiveRecord::Base

  attr_accessible :name, :status_id

  belongs_to :status

end

For status:

class Status < ActiveRecord::Base

  attr_accessible :name

  has_one :book

end

To learn more about association here is the documentation

Now if run the server with:

rails s

and if you go to the following address you will be able to create the three statuses required

http://localhost:3000/statuses

and then go to the url:

http://localhost:3000/books/new

you will see that instead of having status, you have the index, but this is not what we want.

for having the name of the status you have to change something in the view of the book

From your editor open the file app/views/books/_form.html.erb

and this is the code we have to change:

  <div class="field">

    <%= f.label :status_id %><br />

    <%= f.number_field :status_id %>

  </div>

by this one, which basically creates the drop down list for you:

  <div class="field">

    <%= f.label :status_id %><br />

    <%= collection_select :book, :status_id, Status.all, :id,:name,:promp => true  %>

  </div>

The signature of collection_select is this:

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

Basically the two first parameters of collection_select indicate where do you want to save the selection. In this case: Book.status_id
Status.all retrieves all the values from the status table and loads them into the drop down list.
The following two parameters indicate how to create the drop down list, the first is the value, which is the index or primary key of the status, and the second is the text which is the name of the status

For more information on how to use collection select, check out the documentation