Rails Active Record Validation provides a convenient way to validate the state of an object before it is stored in the database. There are various built-in Active Record validations like presence, length, numericality and uniqueness.

By using numericality validator, we can validate an attribute to only have numeric values.

# app/models/blog.rb
class Blog < ApplicationRecord
  validates :likes, numericality: true
end

We can also use helpers like greater_than, greater_than_or_equal_to, equal_to, less_than, less_than_or_equal_to, other_than, odd, even with numericality validator but these work only on numbers.

# app/models/blog.rb
class Blog < ApplicationRecord
  validates :likes, numericality: { greater_than: 1 }
end

Previously for validating comparisons of dates we needed to write custom validators or use a gem like date_validator.

However, Rails 7 has added ComparisonValidator which provides a way to easily validate comparisons with another value, proc, or attribute. Let's assume we have a model Blog with an end_date attribute.

Before

If we want to validate the end_date attribute for the provided value or then we would need to write a custom validator or use a gem like date_validator.

# Using date_validator gem
class Blog < ApplicationRecord
  # validate against provided value
  validates :end_date, date: { after: Proc.new { Date.today } }
  # validate against another attribute
  validates :end_date, date: { after: :start_date }
end

Rails 7 onwards

We can use ComparisonValidator to validate the comparison of the end_date attribute for a provided value.

class Blog < ApplicationRecord
  # validate against provided value
  validates_comparison_of :end_date, greater_than: -> { Date.today }
  # validate against another attribute
  validates :end_date, greater_than: :start_date
end

ComparisonValidator also provides helpers like greater_than, greater_than_or_equal_to, equal_to, less_than, less_than_or_equal_to and other_than.

Check out this pull request for more details.