Program 12:

Build a Rails application to accept book information viz. Accession number, title, authors, edition and publisher from a web page and store the information in a database and to search for a book with the title specified by the user and to display the search results with proper headings.

Procedure for execution:

  • Open a terminal and run mkdir rails_app && cd $_
  • Create a new app called books using the command rails new books -d mysql
  • Run the command cd books/config and open the database.yml file to set mysql username and password by running the command nano database.yml. The username and password are required to be filled at 3 sections in the file.

  • The following is a sample snippet from the database.yml file-

    adapter: mysql2
    encoding: utf8
    reconnect: false
    database: books_development
    pool: 5 username: root
    password: pass
    socket: /var/run/mysqld/mysqld.sock

  • Save the file by ctrl+x and then y.

  • Now run cd .. and make sure that you are present in the rails_app/books directory.
  • Run the command rake db:create
  • Next, run rails generate controller books index
  • Next, run rails generate model book access_no:integer title:string author:string edition:integer publisher:string
  • Run rake db:migrate

  • Now, cd app/views/books and edit the file nano index.html.erb -

  • Also, edit the file nano search.html.erb

  • Now, cd ../../controllers and edit the file nano books_controller.rb
  • Next, run cd ../../config and edit nano routes.rb file.
  • Finally, run cd .. and start the rails server by running the command rails s
  • Open a browser and in the address bar type localhost:3000 to check if the rails server is running. If yes, add to the URL, localhost:3000/books/index.
  • Enter the input & on successfully inserting data, search for the same from the browser. The output is displayed in a table on the browser.

Explaination

  • The rails new command has created a Rails application in a new directory called books
  • The -d options in the rails new command allows us to specify which DBMS to use. The default is sqlite. However we use mysql
  • The database.yml file has all the cofiguration information which allows our application to connect, create and modify the database
  • You run rake db:create once and only once, and you run it first. Then you run rake db:migrate every time you add/change a migration
  • The rails generate controller command created a lot of files and directories. We are interested in two of them for now :-
    • app/controllers/books_controller.rb
    • app/views/books/index.html.erb
  • Inside Rails application, the controller file is placed inside app/controllers directory

  • The Controller

    • User types a URL, lets say http://localhost:3000/pages/home. If the Rails server is running, the request first reaches the Rails router.

    • Alt text

    • The Router checks the config/routes.rb file to see if there is an entry matching the URL requested. In our case there is a route entry - get "pages/home". In short, the route matches incoming URL /pages/home to home action in Pages controller. So the request is forwarded to the Pages controller, home action.

    • Alt text

    • In our program the BooksController is a class. Intially there is an empty method index inside the class. The method is also called index action in the Books controller.

          class BooksController < ApplicationController

    def index

    end

    • This action serves the url /books/index when accessed. Even though the index action is an empty method, it fetches the file /apps/views/books/index.html.erb and displays it on the browser.

  • The Model

    • Rails interact with the database through models. In our program we have a model called Book. This ensures that the our model is independent of the DBMS
    • When you create a model, the name is singular and the name starts with capital letter. Book, instead of Books

    • In our model we have the following attributes

      • access_no:integer
      • title:string
      • author:string
      • edition:integer
      • publisher:string

    • The rails generate model command also creates a migration file present under db/migrate

    • The migration file is like schema which defines the database table structure
    • rake db:migrate pushes the database changes from the migration file to the actual database

    • If you end up doing a mistake you can always undo the creation of a model using

             rails destroy model Book

    • If you want to delete the database from the DBMS once the model has been migrated use 

              rake db:rollback

      • Ruby Tags

      • RoR has the following 2 tags :
        • <% %> : The output of this tag will NOT be displayed on the browser
        • <%= %> : The output will be displayed on the browser

      Code:

      • index.html.erb
    <h1>Books</h1><br>
    <h3 style="text-align: center;">Add a book</h3><br>
    <%= form_tag("/books/add", :method=>"post") do %>  
    <form action="/books/add" method="post"> <br> 
    Access No:<%= text_field_tag(:b_access_no) %>      
    //create input tags of given type and id
    <input type="text" id=":b_access_no"><br>
    <br>Title: <%= text_field_tag(:b_title) %>       
    <input type="text" id=":b_title"><br>
    <br>Author: <%= text_field_tag(:b_author) %>        
    <input type="text" id=":b_author"><br>
    <br>Edition: <%= text_field_tag(:b_edition) %>         
    <input type="text" id=":b_edition"><br>
    <br>Publisher: <%= text_field_tag(:b_publisher) %>   
    <input type="text" id=":b_publisher"><br>
    <br><br> 
    <%= submit_tag("Add Book") %>   
    <input type="submit" value="Add Book"><br>
    <% end %> 
    <br>
    <h3 style="text-align: center;">Search for a book</h3><br>
    <%= form_tag("/books/search", :method=>"post") do %>  
    <form action="/books/search" method="post"><br>
    Title: <%= text_field_tag(:bs_title) %>  
    <input type="text" id=":bs_title"><br>
    <br><br>
    <%= submit_tag("Search") %>   
    <input type="submit" value="Search"><br>
    <% end %>  
    <br>
  • search.html.erb
    <h1>Search Result</h1><br>
    <table border=1><br>
    <% @t=Book.find_by_title(params[:bs_title]) %>  
    //RoR creates a find_by_attribute method for our model. In our case we are asked to search by title hence we are using the find_by_title function. This function takes a string as parameter. Here we are using the the value in :bs_title that was passed on using post method when the button was pressed. This function returns an array. Arrays in ruby begin with the '@' symbol
    <br>
    <tr><br>
    <th>Access No.</th><br>
    <th>Title</th><br>
    <th>Author</th><br>
    <th>Edition</th><br>
    <th>Publisher</th><br>
    </tr><br>
    <tr><br>
     //Elements of an array are accessed by the "." operator followed by the attribute name.
     //In our case we are accessing the access_no that was returned to the array t. 
    <td> <%=  @t.access_no %> </td>   
    <td> <%= @t.title %> </td>  
    <td> <%= @t.author %> </td>  
    <td> <%= @t.edition %> </td>  
    <td> <%= @t.publisher %> </td>  
    </tr><br>
    </table><br>
    <br><br><br>
    <a href="/books/index">Back</a>  
    <br>
  • books_controller.rb
    class BooksController < ApplicationController    
    //auto-generated  code  
    def index   
    //auto-generated  code  
    end   
    //auto-generated  code<br>
    def add   
    //create a new action called add which performs the below action 
    Book.create(:access_no=>params[:b_access_no],:title=>params[:b_title],:author=>params[:b_author],:edition=> params[:b_edition],:publisher=> params[:b_publisher])   
    //the create method is used to add a vlaue to the DB. The values to be added are fetched from the post method using the param function
    redirect_to :action => 'index'  
    //once the add button is clicked this specifes which page is to be displayed.Here the index page is redisplayed  
    end  
    def search   
    //defines the search action. Just displayes search.html.erb on browser  
    end  
    end
  • routes.rb
    Books::Application.routes.draw do   
    //auto generated code  
    match "books/index" => "books#index", :as => :index   
    //use the action defined under index when request for /books/index is recieved<br>
    match  "books/add" => "books#add", :via => :post   
    //use action defined under add when request for books/add is recieved via post method<br>
    match  "books/search" => "books#search", :via => :post   
    //use action defined under search when request for books/search is recieved via post method<br>

Screenshots:

input_1 input_2 output