rails/activemodel/lib/active_model/validator.rb

module ActiveModel #:nodoc:
  # A simple base class that can be used along with ActiveModel::Base.validates_with
  #
  #   class Person < ActiveModel::Base
  #     validates_with MyValidator
  #   end
  #
  #   class MyValidator < ActiveModel::Validator
  #     def validate
  #       if some_complex_logic
  #         record.errors[:base] = "This record is invalid"
  #       end
  #     end
  #
  #     private
  #       def some_complex_logic
  #         # ...
  #       end
  #   end
  #
  # Any class that inherits from ActiveModel::Validator will have access to <tt>record</tt>,
  # which is an instance of the record being validated, and must implement a method called <tt>validate</tt>.
  #
  #   class Person < ActiveModel::Base
  #     validates_with MyValidator
  #   end
  #
  #   class MyValidator < ActiveModel::Validator
  #     def validate
  #       record # => The person instance being validated
  #       options # => Any non-standard options passed to validates_with
  #     end
  #   end
  #
  # To cause a validation error, you must add to the <tt>record<tt>'s errors directly
  # from within the validators message
  #
  #   class MyValidator < ActiveModel::Validator
  #     def validate
  #       record.errors[:base] << "This is some custom error message"
  #       record.errors[:first_name] << "This is some complex validation"
  #       # etc...
  #     end
  #   end
  #
  # To add behavior to the initialize method, use the following signature:
  #
  #   class MyValidator < ActiveModel::Validator
  #     def initialize(record, options)
  #       super
  #       @my_custom_field = options[:field_name] || :first_name
  #     end
  #   end
  class Validator
    attr_reader :options

    def initialize(options)
      @options = options
    end

    def validate(record)
      raise NotImplementedError
    end
  end

  # EachValidator is a validator which iterates through the attributes given
  # in the options hash invoking the validate_each method passing in the
  # record, attribute and value.
  #
  # All ActiveModel validations are built on top of this Validator.
  class EachValidator < Validator
    attr_reader :attributes

    def initialize(options)
      @attributes = options.delete(:attributes)
      super
      check_validity!
    end

    def validate(record)
      attributes.each do |attribute|
        value = record.send(:read_attribute_for_validation, attribute)
        next if (value.nil? && options[:allow_nil]) || (value.blank? && options[:allow_blank])
        validate_each(record, attribute, value)
      end
    end

    def validate_each(record, attribute, value)
      raise NotImplementedError
    end

    def check_validity!
    end
  end

  # BlockValidator is a special EachValidator which receives a block on initialization
  # and call this block for each attribute being validated. +validates_each+ uses this
  # Validator.
  class BlockValidator < EachValidator
    def initialize(options, &block)
      @block = block
      super
    end

    def validate_each(record, attribute, value)
      @block.call(record, attribute, value)
    end
  end
end