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What is Validations in Ruby on Rails?

In this blog, we will discuss an essential aspect of building any application - validations, specifically in the Ruby on Rails framework. If you're new to programming or just diving into Rails, you're in the right place! We will go through the concept of validations and how they can be implemented in Rails, complete with code examples and explanations.

Understanding Validations

Validations are a way to ensure that your application's data is accurate and consistent. Every application relies on data, whether it's user data, product data, or any other type of information. To maintain the integrity of the application, it's important to make sure that this data is valid and adheres to certain rules or criteria.

For example, imagine you are building a social media application where users can sign up and create profiles. You would want to ensure that every user provides a unique email address, a username that is not too long, and a password that meets specific security requirements.

Validations help you enforce these rules and check that the data entered by users is correct before it is saved to your application's database. This ensures that your application runs smoothly and avoids any unexpected behavior or errors due to invalid data.

Validations in Ruby on Rails

Ruby on Rails, often referred to as Rails, is a popular web application framework that helps developers build powerful and scalable applications quickly. Rails has built-in support for validations, making it easy to add them to your application and save time on manual data checking.

In Rails, validations are typically added to your models. A model is a representation of a database table within your application, and it's where you define the structure and behavior of the data you're working with.

Adding validations to your models can be done in a few simple steps. Let's explore this process using our earlier example of a social media application.

Step 1: Create a new Rails application

First, let's create a new Rails application. Open your terminal or command prompt and run the following command:

rails new social_media_app

This will create a new Rails application called "social_media_app" in the current directory.

Step 2: Generate a User model

Next, let's create a User model for our application. In the terminal, navigate to the social_media_app directory and run the following command:

rails generate model User email:string username:string password_digest:string

This command creates a new model called User with the attributes email, username, and password_digest. The password_digest attribute will store an encrypted version of the user's password.

Step 3: Run database migrations

After generating the User model, you need to run database migrations to create the corresponding users table in your application's database. Run the following command in your terminal:

rails db:migrate

Step 4: Add validations to the User model

Now that we have our User model set up, let's add validations to it. Open the user.rb file located in the app/models directory and add the following validations:

class User < ApplicationRecord
  validates :email, presence: true, uniqueness: true
  validates :username, presence: true, length: { maximum: 50 }
  validates :password_digest, presence: true, length: { minimum: 6 }

Let's break down the validations we've added:

validates :email, presence: true, uniqueness: true: This validation ensures that the email attribute is present and unique. In other words, a user must provide an email address, and it must be different from the email addresses of other users.

validates :username, presence: true, length: { maximum: 50 }: This validation ensures that the username attribute is present and has a maximum length of 50 characters.

validates :password_digest, presence: true, length: { minimum: 6 }: This validation ensures that the password_digest attribute is present and has a minimum length of 6 characters.

These validations will help us maintain the integrity of our user data and prevent invalid data from being saved to our database.

Step 5: Test your validations

Now that we've added validations to our User model, let's test them out. Rails provides an easy-to-use console that allows you to interact with your application's models and data. To open the Rails console, run the following command in your terminal:

rails console

Next, let's create a new User instance with invalid data and see if our validations are working. In the Rails console, run the following command:

user = "", username: "testuser", password_digest: "123")

This command creates a new User instance with an empty email, a username of "testuser", and a password_digest of "123". Since our validations require a non-empty email and a password_digest of at least 6 characters, this user should be considered invalid.

To check if our user is valid, run the following command:


This should return false, indicating that our user is indeed invalid.

To see the specific validation errors, you can access the errors attribute of the user instance:


This should return an array containing the error messages:

["Email can't be blank", "Email has already been taken", "Password digest is too short (minimum is 6 characters)"]

As you can see, our validations are working as expected, and we can now be confident that only valid user data will be saved to our database.


Validations are a crucial part of building any application, and Ruby on Rails makes it easy to add them to your models. By using validations, you can ensure that your application's data is accurate and consistent, leading to a smoother user experience and fewer bugs.

In this blog, we covered the basics of validations in Rails, how to add them to your models, and how to test them using the Rails console. With this knowledge, you can now start adding validations to your own Rails applications and improve the overall quality and reliability of your data.