Rails Programmer

Tuesday, February 20, 2018

File uploading

You may have a requirement in which you want your site visitors to upload a file on your server. Rails makes it very easy to handle this requirement. Now we will proceed with a simple and small Rails project.

As usual, let's start off with a new Rails application called testfile. Let's create the basic structure of the application by using simple rails command.

tp> rails new testfile

Before starting application development, we should install gem files as shown below −

gem install carrierwave
gem install bootstrap-sass

Open up your gemfile and add the following two gems at the bottom as shown in the following image −

After adding gems in the gem file, we need to run the following command on the console −

bundle install

Creating the Model

We need to create a model with two strings as name and attachment as shown below −

rails g model Resume name:string attachment:string

We need to create the database migration as shown below −

rake db:migrate

We need to generate the controller as shown below −

rails g controller Resumes index new create destroy

Great! Now we have the basic structure set up. Now we need to create an uploader. An Uploader came from carrierwave gem and it tells to carrierwave how to handle the files. In short, it contained all file processing functionalities. Run the command to create an uploader as shown below

rails g uploader attachment

Now open the resume model and call the uploader as shown below. Resume model has placed at app/models/resume.rb −

class Resume < ActiveRecord::Base
   mount_uploader :attachment, AttachmentUploader # Tells rails to use this uploader for this model.
   validates :name, presence: true # Make sure the owner's name is present.
end

Before working on controller, we need to modify our config/routes.db as shown below −

CarrierWaveExample::Application.routes.draw do
   resources :resumes, only: [:index, :new, :create, :destroy]
   root "resumes#index"
end

Lets us edit the controller as shown below.

class ResumesController < ApplicationController
   def index
      @resumes = Resume.all
   end
   
   def new
      @resume = Resume.new
   end
   
   def create
      @resume = Resume.new(resume_params)
      
      if @resume.save
         redirect_to resumes_path, notice: "The resume #{@resume.name} has been uploaded."
      else
         render "new"
      end
      
   end
   
   def destroy
      @resume = Resume.find(params[:id])
      @resume.destroy
      redirect_to resumes_path, notice:  "The resume #{@resume.name} has been deleted."
   end
   
   private
      def resume_params
      params.require(:resume).permit(:name, :attachment)
   end
   
end

Let's add bootstrap implementation in css file.css file could be in app/assets/stylesheets/resumes.css.scss

@import "bootstrap";

Now open up app/views/layouts/application.html.erb and add codes as shown below −

<!DOCTYPE html>
<html>
   
   <head>
      <title>Tutorialspoint</title>
      <%= stylesheet_link_tag "application", media: "all", "data-turbolinks-track" => true %>
      <%= javascript_include_tag "application", "data-turbolinks-track" => true %>
      <%= csrf_meta_tags %>
   </head>
   
   <body>
      <div class = "container" style = "padding-top:20px;">
         <%= yield %>
      </div>
   </body>

</html>

Now we need to set up index views as shown below −

<% if !flash[:notice].blank? %>
   <div class = "alert alert-info">
      <%= flash[:notice] %>
   </div>
<% end %>

<br />

<%= link_to "New Resume", new_resume_path, class: "btn btn-primary" %>
<br />
<br />

<table class = "table table-bordered table-striped">
   <thead>.
      <tr>
         <th>Name</th>
         <th>Download Link</th>
         <th> </th>
      </tr>
   </thead>
   
   <tbody>
      <% @resumes.each do |resume| %>
         
         <tr>
            <td><%= resume.name %></td>
            <td><%= link_to "Download Resume", resume.attachment_url %></td>
            <td><%= button_to "Delete",  resume, method: :delete, class: "btn btn-danger", confirm: "Are you sure that you wish to delete #{resume.name}?" %></td>
         </tr>
         
      <% end %>
   </tbody>
   
</table>

Now, lets edit new.html.erb and add our form code.

<% if !@resume.errors.empty? %>
   <div class = "alert alert-error">
      
      <ul>
         <% @resume.errors.full_messages.each do |msg| %>
            <li><%= msg %></li>
         <% end %>
      </ul>
      
   </div>
<% end %>

<div class = "well">
   <%= form_for @resume, html: { multipart: true } do |f| %>
      <%= f.label :name %>
      <%= f.text_field :name %>
      <%= f.label :attachment %>
      <%= f.file_field :attachment %>
      <%= f.submit "Save", class: "btn btn-primary" %>
   <% end %>
</div>

Now start the server and visit http://localhost:3000. It will produce a screen similar to as follows −

One last thing we need to do is filter the list of allowed filetypes. For that we need add simple code as shown below at app/uploaders/attachment_uploader.rb

class AttachmentUploader < CarrierWave::Uploader::Base
   storage :file
   
   def store_dir
      "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
   end
   
   def extension_white_list
      %w(pdf doc htm html docx)
   end
end

Now start the server and visit http://localhost:3000. Now input a wrong format; it will generate a wrong message as shown below −

Sunday, February 4, 2018

AJAX

Ajax stands for Asynchronous JavaScript and XML. Ajax is not a single technology; it is a suite of several technologies. Ajax incorporates the following −

XHTML for the markup of web pages
CSS for the styling
Dynamic display and interaction using the DOM
Data manipulation and interchange using XML
Data retrieval using XMLHttpRequest
JavaScript as the glue that meshes all this together

Ajax enables you to retrieve data for a web page without having to refresh the contents of the entire page. In the basic web architecture, the user clicks a link or submits a form. The form is submitted to the server, which then sends back a response. The response is then displayed for the user on a new page.

When you interact with an Ajax-powered web page, it loads an Ajax engine in the background. The engine is written in JavaScript and its responsibility is to both communicate with the web server and display the results to the user. When you submit data using an Ajax-powered form, the server returns an HTML fragment that contains the server's response and displays only the data that is new or changed as opposed to refreshing the entire page.

For a complete detail on AJAX you can go through our AJAX Tutorial

How Rails Implements Ajax

Rails has a simple, consistent model for how it implements Ajax operations. Once the browser has rendered and displayed the initial web page, different user actions cause it to display a new web page (like any traditional web application) or trigger an Ajax operation −

Some trigger fires − This trigger could be the user clicking on a button or link, the user making changes to the data on a form or in a field, or just a periodic trigger (based on a timer).
The web client calls the server − A JavaScript method, XMLHttpRequest, sends data associated with the trigger to an action handler on the server. The data might be the ID of a checkbox, the text in an entry field, or a whole form.
The server does processing − The server-side action handler ( Rails controller action )-- does something with the data and returns an HTML fragment to the web client.
The client receives the response − The client-side JavaScript, which Rails creates automatically, receives the HTML fragment and uses it to update a specified part of the current page's HTML, often the content of a <div> tag.

These steps are the simplest way to use Ajax in a Rails application, but with a little extra work, you can have the server return any kind of data in response to an Ajax request, and you can create custom JavaScript in the browser to perform more involved interactions.

AJAX Example

This example works based on scaffold, Destroy concept works based on ajax.

In this example, we will provide, list, show and create operations on ponies table. If you did not understand the scaffold technology then we would suggest you to go through the previous chapters first and then continue with AJAX on Rails.

Creating An Application

Let us start with the creation of an application It will be done as follows −

rails new ponies

The above command creates an application, now we need to call the app directory using with cd command. It will enter in to an application directory then we need to call a scaffold command. It will be done as follows −

rails generate scaffold Pony name:string profession:string

Above command generates the scaffold with name and profession column. We need to migrate the data base as follows command

rake db:migrate

Now Run the Rails application as follows command

rails s

Now open the web browser and call a url as http://localhost:3000/ponies/new, The output will be as follows

Creating an Ajax

Now open app/views/ponies/index.html.erb with suitable text editors. Update your destroy line with :remote => true, :class => 'delete_pony'.At finally, it looks like as follows.

Create a file, destroy.js.erb, put it next to your other .erb files (under app/views/ponies). It should look like this −

Now enter the code as shown below in destroy.js.erb

$('.delete_pony').bind('ajax:success', function() {
   $(this).closest('tr').fadeOut();
});

Now Open your controller file which is placed at app/controllers/ponies_controller.rb and add the following code in destroy method as shown below −

# DELETE /ponies/1
# DELETE /ponies/1.json
def destroy
   @pony = Pony.find(params[:id])
   @pony.destroy
   
   respond_to do |format|
      format.html { redirect_to ponies_url }
      format.json { head :no_content }
      format.js   { render :layout => false }
   end
   
end

At finally controller page is as shown image.

Now run an application, Output called from http://localhost:3000/ponies/new, it will looks like as following image

Press on create pony button, it will generate the result as follows

Now click on back button, it will show all pony created information as shown image

Till now, we are working on scaffold, now click on destroy button, it will call a pop-up as shown below image, the pop-up works based on Ajax.

If Click on ok button, it will delete the record from pony. Here I have clicked ok button. Final output will be as follows −

Thursday, November 23, 2017

Ruby on Rails - Scaffolding

While you're developing Rails applications, especially those which are mainly providing you with a simple interface to data in a database, it can often be useful to use the scaffold method.

Scaffolding provides more than cheap demo thrills. Here are some benefits −

You can quickly get code in front of your users for feedback.
You are motivated by faster success.
You can learn how Rails works by looking at the generated code.
You can use scaffolding as a foundation to jump start your development.

Scaffolding Example

To understand scaffolding, let's create a database called cookbook and a table called recipes.

Creating an Empty Rails Web Application

Open a command window and navigate to where you want to create this cookbook web application. So, run the following command to create a complete directory structure.

tp> rails new cookbook

Setting up the Database

Here is the way to create a database −

mysql> create database cookbook;
Query OK, 1 row affected (0.01 sec)

mysql> grant all privileges on cookbook.*
to 'root'@'localhost' identified by 'password';
Query OK, 0 rows affected (0.00 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

To instruct Rails how to find the database, edit the configuration file cookbook\config\database.yml and change the database name to cookbook. Leave the password empty. When you finish, it should look as follows −

development:
   adapter: mysql
   database: cookbook
   username: root
   password: [password]
   host: localhost
 
test:
   adapter: mysql
   database: cookbook
   username: root
   password: [password]
   host: localhost
 
production:
   adapter: mysql
   database: cookbook
   username: root
   password: [password]
   host: localhost

Rails lets you run in the development mode, test mode, or production mode, using different databases. This application uses the same database for each.

The Generated Scaffold Code

With the scaffold action, Rails generates all the code it needs dynamically. By running scaffold as a script, we can get all the code written to disk, where we can investigate it and then start tailoring it to our requirements.

So now, let's start once again to generate Scaffold code manually by using the scaffold helper script −

cookbook> rails generate scaffold recipe

It generates auto-files as shown below −

The Controller

Let's look at the code behind the controller. This code is generated by the scaffold generator. If you open app/controllers/recipes_controller.rb, then you will find something as follows −

class RecipesController < ApplicationController
   before_action :set_recipe, only: [:show, :edit, :update, :destroy]
   
   # GET /recipes
   # GET /recipes.json
   def index
      @recipes = Recipe.all
   end
   
   # GET /recipes/1
   # GET /recipes/1.json
   def show
   end
   
   # GET /recipes/new
   def new
      @recipe = Recipe.new
   end
   
   # GET /recipes/1/edit
   def edit
   end
   
   # POST /recipes
   # POST /recipes.json
   def create
      @recipe = Recipe.new(recipe_params)
      
      respond_to do |format|
         if @recipe.save
            format.html { redirect_to @recipe, notice: 'Recipe was successfully created.' }
            format.json { render :show, status: :created, location: @recipe }
         else
            format.html { render :new }
            format.json { render json: @recipe.errors, status: :unprocessable_entity }
         end
      end
      
   end
   
   # PATCH/PUT /recipes/1
   # PATCH/PUT /recipes/1.json
   def update
      respond_to do |format|
         if @recipe.update(recipe_params)
            format.html { redirect_to @recipe, notice: 'Recipe was successfully updated.' }
            format.json { render :show, status: :ok, location: @recipe }
         else
            format.html { render :edit }
            format.json { render json: @recipe.errors, status: :unprocessable_entity }
         end
      end
      
   end
   
   # DELETE /recipes/1
   # DELETE /recipes/1.json
   def destroy
      @recipe.destroy
         respond_to do |format|
         format.html { redirect_to recipes_url, notice: 'Recipe was successfully destroyed.' }
         format.json { head :no_content }
      end
   end
   
   private
   
   # Use callbacks to share common setup or constraints between actions.
   def set_recipe
      @recipe = Recipe.find(params[:id])
   end
   
   # Never trust parameters from the scary internet, only allow the white list through.
   def recipe_params
      params.require(:recipe).permit(:tittle, :instructions)
   end
end

When the user of a Rails application selects an action, e.g. "Show" - the controller will execute any code in the appropriate section - "def show" - and then by default will render a template of the same name - "show.html.erb". This default behavior can be overwritten.

The controller uses ActiveRecord methods such as find, find_all, new, save, update_attributes, and destroy to move data to and from the database tables. Note that you do not have to write any SQL statements, rails will take care of it automatically.

This single line of code will bring the database table to life. It will provide with a simple interface to your data, and ways of −

Creating new entries
Editing current entries
Viewing current entries
Destroying current entries

When creating or editing an entry, scaffold will do all the hard work like form generation and handling for you, and will even provide clever form generation, supporting the following types of inputs −

Simple text strings
Text areas (or large blocks of text)
Date selectors
Date-time selectors

You can use Rails Migrations to create and maintain tables.

rake db:migrate RAILS_ENV=development

Now, go to the cookbook directory and run the Web Server using the following command −

cookbook> rails server

Now, open a browser and navigate to http://127.0.0.1:3000/recipe/new.This will provide you a screen to create new entries in the recipes table. A screenshot is shown below −

Once you press the Create button to create a new recipe, your record is added into the recipes table and it shows the following result −

You can see the option to edit, show, and destroy the records. So, play around with these options.

You can also list down all the recipes available in the recipes table using the URL http://127.0.0.1:3000/recipe/list.

Enhancing the Model

Rails gives you a lot of error handling for free. To understand this, add some validation rules to the empty recipe model −

Modify app/models/recipe.rb as follows and then test your application −

class Recipe < ActiveRecord::Base
   validates_length_of :title, :within => 1..20
   validates_uniqueness_of :title, :message => "already exists"
end

These entries will give automatic checking.

validates_length_of − the field is not blank and not too long.
validates_uniqueness_of − duplicate values are trapped. Instead of the default Rails error message, we have given a custom message here.

Alternative Way to Create Scaffolding

Create an application as shown above and The Generated Scaffold Code as shown below

rails g scaffold Recipe tittle:string instructions:text

Above code generates the auto files with data base by using with sqlite3 with tittle and instruction column as shown below an image.

we need to migrate the data base by using below syntax.

$ rake db:migrate RAILS_ENV=development

Finally run the application by using the following command line −

rails server

It will generate the result as shown above output images.

The Views

All the views and corresponding all the controller methods are created by scaffold command and they are available in the app/views/recipes directory.

How Scaffolding is Different?

If you have gone through the previous chapters, then you must have seen that we had created methods to list, show, delete and create data etc., but scaffolding does that job automatically.