validate

# File activemodel/lib/active_model/validations.rb, line 171
      def validate(*args, &block)
        options = args.extract_options!

        if args.all?(Symbol)
          options.each_key do |k|
            unless VALID_OPTIONS_FOR_VALIDATE.include?(k)
              raise ArgumentError.new("Unknown key: #{k.inspect}. Valid keys are: #{VALID_OPTIONS_FOR_VALIDATE.map(&:inspect).join(', ')}. Perhaps you meant to call `validates` instead of `validate`?")
            end
          end
        end

        if options.key?(:on)
          options = options.merge(if: [predicate_for_validation_context(options[:on]), *options[:if]])
        end

        set_callback(:validate, *args, options, &block)
      end

      # List all validators that are being used to validate the model using
      # +validates_with+ method.
      #
      #   class Person
      #     include ActiveModel::Validations
      #
      #     validates_with MyValidator
      #     validates_with OtherValidator, on: :create
      #     validates_with StrictValidator, strict: true
      #   end
      #
      #   Person.validators
      #   # => [
      #   #      #<MyValidator:0x007fbff403e808 @options={}>,
      #   #      #<OtherValidator:0x007fbff403d930 @options={on: :create}>,
      #   #      #<StrictValidator:0x007fbff3204a30 @options={strict:true}>
      #   #    ]
      def validators
        _validators.values.flatten.uniq
      end

      # Clears all of the validators and validations.
      #
      # Note that this will clear anything that is being used to validate
      # the model for both the +validates_with+ and +validate+ methods.
      # It clears the validators that are created with an invocation of
      # +validates_with+ and the callbacks that are set by an invocation
      # of +validate+.
      #
      #   class Person
      #     include ActiveModel::Validations
      #
      #     validates_with MyValidator
      #     validates_with OtherValidator, on: :create
      #     validates_with StrictValidator, strict: true
      #     validate :cannot_be_robot
      #
      #     def cannot_be_robot
      #       errors.add(:base, 'A person cannot be a robot') if person_is_robot
      #     end
      #   end
      #
      #   Person.validators
      #   # => [
      #   #      #<MyValidator:0x007fbff403e808 @options={}>,
      #   #      #<OtherValidator:0x007fbff403d930 @options={on: :create}>,
      #   #      #<StrictValidator:0x007fbff3204a30 @options={strict:true}>
      #   #    ]
      #
      # If one runs <tt>Person.clear_validators!</tt> and then checks to see what
      # validators this class has, you would obtain:
      #
      #   Person.validators # => []
      #
      # Also, the callback set by <tt>validate :cannot_be_robot</tt> will be erased
      # so that:
      #
      #   Person._validate_callbacks.empty?  # => true
      #
      def clear_validators!
        reset_callbacks(:validate)
        _validators.clear
      end

      # List all validators that are being used to validate a specific attribute.
      #
      #   class Person
      #     include ActiveModel::Validations
      #
      #     attr_accessor :name, :age
      #
      #     validates_presence_of :name
      #     validates_inclusion_of :age, in: 0..99
      #   end
      #
      #   Person.validators_on(:name)
      #   # => [
      #   #       #<ActiveModel::Validations::PresenceValidator:0x007fe604914e60 @attributes=[:name], @options={}>,
      #   #    ]
      def validators_on(*attributes)
        attributes.flat_map do |attribute|
          _validators[attribute.to_sym]
        end
      end

      # Returns +true+ if +attribute+ is an attribute method, +false+ otherwise.
      #
      #  class Person
      #    include ActiveModel::Validations
      #
      #    attr_accessor :name
      #  end
      #
      #  User.attribute_method?(:name) # => true
      #  User.attribute_method?(:age)  # => false
      def attribute_method?(attribute)
        method_defined?(attribute)
      end

      # Copy validators on inheritance.
      def inherited(base) # :nodoc:
        dup = _validators.dup
        base._validators = dup.each { |k, v| dup[k] = v.dup }
        super
      end

      private
        @@predicates_for_validation_contexts = {}

        def predicate_for_validation_context(context)
          context = context.is_a?(Array) ? context.sort : Array(context)

          @@predicates_for_validation_contexts[context] ||= -> (model) do
            if model.validation_context.is_a?(Array)
              model.validation_context.any? { |model_context| context.include?(model_context) }
            else
              context.include?(model.validation_context)
            end
          end
        end
    end