validates_with

Passes the record off to the class or classes specified and allows them to add errors based on more complex conditions.

class Person
  include ActiveModel::Validations
  validates_with MyValidator
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    if some_complex_logic
      record.errors.add :base, 'This record is invalid'
    end
  end

  private
    def some_complex_logic
      # ...
    end
end

You may also pass it multiple classes, like so:

class Person
  include ActiveModel::Validations
  validates_with MyValidator, MyOtherValidator, on: :create
end

There is no default error message for validates_with. You must manually add errors to the record’s errors collection in the validator class.

To implement the validate method, you must have a record parameter defined, which is the record to be validated.

Configuration options:

• :on - Specifies the contexts where this validation is active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. on: :create or on: :custom_validation_context or on: [:create, :custom_validation_context])

• :if - Specifies a method, proc, or string to call to determine if the validation should occur (e.g. if: :allow_validation, or if: Proc.new { |user| user.signup_step > 2 }). The method, proc, or string should return or evaluate to a true or false value.

• :unless - Specifies a method, proc, or string to call to determine if the validation should not occur (e.g. unless: :skip_validation, or unless: Proc.new { |user| user.signup_step <= 2 }). The method, proc, or string should return or evaluate to a true or false value.

• :strict - Specifies whether validation should be strict. See ActiveModel::Validations#validates! for more information.

If you pass any additional configuration options, they will be passed to the class and available as options:

class Person
  include ActiveModel::Validations
  validates_with MyValidator, my_custom_key: 'my custom value'
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    options[:my_custom_key] # => "my custom value"
  end
end

# File activemodel/lib/active_model/validations/with.rb, line 88
      def validates_with(*args, &block)
        options = args.extract_options!
        options[:class] = self

        args.each do |klass|
          validator = klass.new(options.dup, &block)

          if validator.respond_to?(:attributes) && !validator.attributes.empty?
            validator.attributes.each do |attribute|
              _validators[attribute.to_sym] << validator
            end
          else
            _validators[nil] << validator
          end

          validate(validator, options)
        end
      end