module ActiveModel::Validations

# File activemodel/lib/active_model/validations.rb, line 301
def errors
  @errors ||= Errors.new(self)
end

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

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates_presence_of :name
end

person = Person.new
person.valid? # => false
person.errors # => #<ActiveModel::Errors:0x007fe603816640 @messages={name:["can't be blank"]}>

# File activemodel/lib/active_model/validations.rb, line 373
def invalid?(context = nil)
  !valid?(context)
end

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

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates_presence_of :name
end

person = Person.new
person.name = ''
person.invalid? # => true
person.name = 'david'
person.invalid? # => false

Context can optionally be supplied to define which callbacks to test against (the context is defined on the validations using :on).

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates_presence_of :name, on: :new
end

person = Person.new
person.invalid?       # => false
person.invalid?(:new) # => true

# File activemodel/lib/active_model/validations.rb, line 334
def valid?(context = nil)
  current_context, self.validation_context = validation_context, context
  errors.clear
  run_validations!
ensure
  self.validation_context = current_context
end

Runs all the specified validations and returns true if no errors were added otherwise false.

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates_presence_of :name
end

person = Person.new
person.name = ''
person.valid? # => false
person.name = 'david'
person.valid? # => true

Context can optionally be supplied to define which callbacks to test against (the context is defined on the validations using :on).

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates_presence_of :name, on: :new
end

person = Person.new
person.valid?       # => true
person.valid?(:new) # => false

# File activemodel/lib/active_model/validations.rb, line 382
def validate!(context = nil)
  valid?(context) || raise_validation_error
end

Runs all the validations within the specified context. Returns true if no errors are found, raises ValidationError otherwise.

Validations with no :on option will run no matter the context. Validations with some :on option will only run in the specified context.

# File activemodel/lib/active_model/validations/with.rb, line 137
def validates_with(*args, &block)
  options = args.extract_options!
  options[:class] = self.class

  args.each do |klass|
    validator = klass.new(options, &block)
    validator.validate(self)
  end
end

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

  validate :instance_validations

  def instance_validations
    validates_with MyValidator
  end
end

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

You may also pass it multiple classes, like so:

class Person
  include ActiveModel::Validations

  validate :instance_validations, on: :create

  def instance_validations
    validates_with MyValidator, MyOtherValidator
  end
end

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

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