How can I implement custom validations in Rails 6?

How can I implement custom validations in Rails 6?

In Rails 6, you can create custom validations by defining a method in your model and using the validate method.

Can you give me an example of a custom validation?

Sure! For instance, if you want to validate that a username is not 'admin', you could do this:

class User < ApplicationRecord
  validate :username_cannot_be_admin

  private

  def username_cannot_be_admin
    if username == 'admin'
      errors.add(:username, 'cannot be admin')
    end
  end
end

What if I want to add multiple custom validations?

You can add multiple custom validations by defining more methods and calling validate for each one. For example:

class User < ApplicationRecord
  validate :username_cannot_be_admin, :email_must_be_valid

  private

  def username_cannot_be_admin
    errors.add(:username, 'cannot be admin') if username == 'admin'
  end

  def email_must_be_valid
    errors.add(:email, 'must be a valid email') unless email =~ /[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b/i
  end
end