Custom validator to allow creation of a record with duplicate content if it has been flagged as deleted.

paranoid_uniqueness_validator.rb

# Custom validator to allow for duplicate content on an attribute in a class using acts_as_paranoid gem.
#
# Scenario: 
# A user can create a record with an attribute with given content 'test'
# if a previous record with that attribute/content does not exist or if it does exist but was flagged as deleted (deleted_at IS NOT NULL)
#
# Usage:
# validates :attribute, paranoid_uniqueness: true
# or
# validates :attribute, paranoid_uniqueness: { scope: platform_id, message: 'custom message }
# Note scope and message is optional (obviously), If it needs to work with additional options, it will need to be built as required.

class ParanoidUniquenessValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    scope = options[:scope]
    query = { attribute => record[attribute], deleted_at: nil }
    
    query.merge!(scope => record[scope]) if scope
    
    if record.class.with_deleted.where(query).any?
      record.errors.add attribute, (options[:message] || 'has already been taken')
    end
  end
end