module ActiveModel::Validations

Returns the Errors object that holds all information about attribute error messages.

def errors
  @errors ||= Errors.new(self)
end

false otherwise.
Performs the opposite of valid?. Returns true if errors were added,

def invalid?(context = nil)
  !valid?(context)
end

def run_validations!
  _run_validate_callbacks
  errors.empty?
end

to test against (the context is defined on the validations using :on).
otherwise false. Context can optionally be supplied to define which callbacks
Runs all the specified validations and returns true if no errors were added

def valid?(context = nil)
  current_context, self.validation_context = validation_context, context
  errors.clear
  run_validations!
ensure
  self.validation_context = current_context
end

class version of this method for more information
to the class and available as options, please refer to the
If you pass any additional configuration options, they will be passed

in the callback
placed on the validates method as these are applied and tested
available on the class version of validates_with, should instead be
Standard configuration options (:on, :if and :unless), which are

end
end
validates_with MyValidator, MyOtherValidator
def instance_validations

validates :instance_validations, :on => :create

include ActiveModel::Validations
class Person

You may also pass it multiple classes, like so:

creating your own validator.
Please consult the class method documentation for more information on

end
end
validates_with MyValidator
def instance_validations

validates :instance_validations

include ActiveModel::Validations
class Person

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

def validates_with(*args, &block)
  options = args.extract_options!
  args.each do |klass|
    validator = klass.new(options, &block)
    validator.validate(self)
  end
end