What is a "validation"?

In terms of strict English, a validation is a method that serves as a way of confirming something is what it is before anything else happens.

"Does this dress look good on me? I want to validate that it's not tacky and okay to wear to the party."

Definitely not the most normal human interaction but you get it.

Validations in code are essentially the same thing! They consist of code that protects the database from receiving invalid data that may harm the database or other aspects of the application.

We implement validations to assure ourselves that we are receiving the correct information every time.

One method of validations can be handled through ActiveRecord, which we will discuss in a later blog. For now, this is how it will look.

Basic Usage

 class Person < ActiveRecord::Base
   validates :name, presence: true
 end 

#validates is doing exactly what it looks like it's doing. It is accepting the name of the attribute that we want to validate (:name) and accepting a hash of options that includes the details of the validation. { presence: true } is a very basic validation that checks that there is at least something present for the :name attribute.

Well, writing validations is nice, but, how do we even know if something is validated or not?

We can check manually with #valid?

class Person < Active Record::Base
  validates :name, presence: true
end

person = Person.new
person.valid? #=> false

Above, we created a new person and set it equal to person. We then called #valid? on our new person and returned a value of false. Why is it false? Let's check with errors.messages!

person = Person.new
person.errors.messages #=> name: can't be blank

We did not create a new person with a name, therefore, failing the validation of { presence: true } in reference to the name attribute.

To give our users more information on the validation error, we can also render our validation errors as JSON in our controllers, which will be discussed in another blog post.

def create
  person = Person.create(person_params)
  if person.valid?
    render json: person, status: :created
  else
    render json: { error: person.errors }, status: :unprocessable_entity
  end
end

render json: { error: person.errors } : This line of code is doing exactly what we did before when we called person.errors.messages but displaying it as JSON for the user to see on their end, the frontend.

Other Built-In Validators

Length

length is one of the most versatile because most inputs, if not all, will be a certain amount of characters long.

class Person < Active Record::Base
  validates :name, length: { minimum: 2 }
  validates :bio, length: { maximum: 500 }
  validates :password, length: { in: 6..20 }
  validates :registration_number, length: { is: 6 }
end

Uniqueness

uniqueness is also very common as it is used to ensure that the same username or email cannot be used for more than user account.

class Account < Active Record::Base
  validates :email, uniqueness: true
end

Custom Messages

class Alien < Active Record::Base
  validates :not_a_human, acceptance: true, message: "Extraterrestrials only!"
end

You can say whatever you want for the errors! Make it yours!

Conclusion

We covered the importance of validations and why they are necessary for any application worth using. If you want a secure database, validations must be implemented. If you want to feel safe as a consumer, make sure the applications that use have validations implemented. We went over common validation methods and use-cases.

Resources

https://guides.rubyonrails.org/active_record_validations.html

https://web-crunch.com/posts/understanding-ruby-on-rails-activerecord-validations