Dirtiness Validator validates the value of the specified attribute against its previous value.

Add this line to your application's Gemfile:

gem 'dirtiness_validator'

And then execute:

$ bundle

Or install it yourself as:

$ gem install dirtiness_validator

Pass dirtiness option to the validates method of your ActiveRecord model.

class Vote < ActiveRecord::Base
  validates :count, dirtiness: { greater: true }
  validates :last_voted_at, dirtiness: { greater: true, message: 'is invalid.' }
end

Configuration options other than :message can be supplied with a symbol or a proc.

# This validates that last_voted_at.to_date is greater than last_voted_at_was.to_date.
validates :last_voted_at, dirtiness: { greater: :to_date }

# This does the same.
validates :last_voted_at, dirtiness: { greater: -> (value) { value.to_date } }

Note that Dirtiness Validator skips validation if the record is not persisted.

To use Dirtiness Validator with ActiveModel, you must include ActiveModell:Dirty and call its methods as instructed in your model. Your model's #persisted? method should return true if the changes to the its attributes are ever applied; otherwise Dirtiness Validator never invokes its validation.

class Vote
  include ActiveModel::Validations
  include ActiveModel::Dirty

  validates :count, dirtiness: { greater_or_equal: true }

  def count
    @count
  end

  def count=(val)
    return if @count == val
    count_will_change!
    @count = val
  end

  def save
    changes_applied
    @persisted = true
  end

  def persisted?
    !!@persisted
  end
end

• :message - A custom error message.

• :greater - Specifies the value must be greater than the previous value.

• :greater_or_equal - Specifies the value must be greater than or equal the previous value.

• :equal - Specifies the value must be equal to the previous value.

• :not_equal - Specifies the value must be other than the previous value.

• :less - Specifies the value must be less than the previous value.

• :less_or_equal - Specifies the value must be less than or equal the previous value.

There is also a list of default options for every validator: :if, :unless, :on, :allow_nil, :allow_blank, and :strict.

Bug reports and pull requests are welcome on GitHub at https://github.com/tyamagu2/dirtiness_validator. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.