Comparison Validator in Rails 7

Comparison with another value, proc, or attribute.

ActiveRecord Validations are the most widely used and well-known functionality in Rails. It provides a complete validation framework to validate the state of an object before it is saved in the database. There are various ActiveRecord Validators like presence , uniqueness , length and so on…

If you had a scenario of validating an attribute with some value, in the older versions of Rails we had to write our own custom validations for the same. However, Rails 7 has now added ComparisonValidtor. This provides us with an easy way to validate a comparison between two comparable values. This validator requires an option[value, proc, or symbol] to be supplied for comparing.

Let's assume we have a model appointment where we have attributes start_date and end_date along with others.

Before
If you had to validate end_date attribute for any provided value or another attribute, we had to write the custom validation as shown below:

class Appointment < ApplicationRecord

  validates :start_date, presence: true
  validates :end_date, presence: true
  validate :end_date_is_after_start_date
  def end_date_is_after_start_date
    if end_date < start_date
      errors.add(:end_date, 'can not be before the start 
                 date')
    end
  end
end

With Rails 7
You don't need to use any custom validation and the ComparisonValidtor comes to the rescue. Let's rewrite using the comparison

class Appointment < ApplicationRecord
  validates :start_date, presence: true
  validates :end_date, presence: true
  validates :end_date, comparison: { greater_than: :start_date }
  # OR
  validates_comparison_of :end_date, greater_than: :start_date
end

ComparisonValidator provides support to the below-mentioned options:

• greater_than : Specifies that the value must be greater than the supplied value. The default error message would be “must be greater than %{value}”.

• greater_than_or_equal_to : Specifies that the value must be greater or equal to the supplied value. The default error message is “must be greater than or equal to %{value}”.

• equals_to : Specifies that the value should be equal to the supplied value.

• less_than : Specifies that the value should be less than the supplied value.

• less_than_or_equal_to : This signifies that the value should be less than or equal to the supplied value.

• other_than : Specifies that the value must be other than the supplied value. The default error message is “must be other than the %{value}”

Can we combine multiple Compare options?
Yes, absolutely! We can combine multiple compare options.

Let's say that the end_date must be greater than the start_date and also, wants to validate that the end_date is not today.

class Appointment < ApplicationRecord
  validates :start_date, presence: true
  validates :end_date, presence: true
  validates_comparison_of :end_date, greater_than: 
   :start_date, other_than: Date.today
end

Is ComparisonValidator only for date comparison?
Absolutely no, we can compare numeric , date and as well as the string values with the ComparisonValidator.

class Author < ApplicationRecord
   validates_comparison_of :books_count, greater_than: 5
end

ComparisonValidator is definitely a great addition to Rails 7. As it allows us to compare the data without being to write the custom validations and validates the data effortlessly.

Happy Coding!!❤️