How to add validation in ruby on rails (#part3)

What Will I Learn?

You will learn how to add validation in Ruby on Rails Project such as in forms, models and in database.
You will learn how to migrate and rollback your migrations in ruby on rails project
You will learn some basic MySQL command

Requirements

OS: Ubuntu/Mac OS
A text editor like sublime
Basic understanding about Ruby on Rails
And for better understanding must refer my previous tutorials (link added to the curriculum)

Difficulty

Intermediate

Tutorial Contents

Hello and welcome to the next part of the tutorial. In this tutorial, we will learn how to add validations in our project.

But before that one question may arise that why we use validations?
The answer is that to ensure that only valid and right data should be saved into the database.

We can add severals levels of validations in our project. We will go through every aspect of validation in this tutorial, so let's start the tutorial.

Firstly go to the rails app and start the server in the terminal, that was build in my previous tutorials
And also the open project in a text editor (Sublime text)
Enter the following URL in the browser

 localhost:3000/users/sign_up

You will see the sign-up form as seen below
When you fill up the form details except for user first and last name, the app does not give you an error and it will save the user normally, see below

You can see that new user is created but without its name, because we did not add any validations for that

So let's start adding the validations,

Firstly we will add validation in models so that required field's can not be saved blank, for that

go to app > models > user.rb and save the following code

 validates_presence_of :first_name, :last_name

If you want to validate many fields in one line that you can use this type of format

    validates :first_name, presence: { message: "is required." }
    validates :last_name, presence: { message: "is required." }

If you want to validate individual fields with the custom message that you can use this type of format

And if the user tried to submit the form, the app will show error like this

Model-level validation is very important because the user can bypass the front end validations

Now we will add validation in forms so that required field's can not be submit it blank, for that
Just add required: true in the input type fields.

And now if the user submits the form with a blank username then the following error will be shown

And lastly we will add validation at database
Database validations are required when someone tried to alter the database directly
You see if the form is submitted without email, it gives the error because devise by default add some database level validations
But we added the username field later and it is already migrated so for that we have to rollback our database
Stop the server and run the following command

rake db:rollback

It shows the info as shown below

Now go to your app > db > migrate > your add fields to user migrate name file and change the code as below and save it

class AddFieldsToUser < ActiveRecord::Migration
  def change
    add_column :users, :first_name, :string, null: false
    add_column :users, :last_name, :string, null: false
    add_column :users, :mobile_number, :integer
  end
end

Or you can refer image below
Now run the following command to migarte our database

rake db:migrate

It will migrate the database
And now if someone tried to save the username blank directly from the database, it won't be able to do that
So let's have a try on it, open the terminal and go to your project path and enter into MySQL console