class ActiveModel::Errors

# etc..
person.errors.full_messages # => [“name cannot be nil”]
person.validate! # => [“cannot be nil”]
person = Person.new
The above allows you to do:
for you.
ActiveModel::Validations will handle the validation related methods
you will not need to implement the last two. Likewise, using
languages. Of course, if you extend your object with ActiveModel::Translation
able to generate error messages correctly and also handle multiple
The last three methods are required in your object for Errors to be

end
end
[self]
def self.lookup_ancestors
end
attr
def self.human_attribute_name(attr, options = {})
end
send(attr)
def read_attribute_for_validation(attr)
# The following methods are needed to be minimally implemented
end
errors.add(:name, :blank, message: “cannot be nil”) if name.nil?
def validate!
attr_reader :errors
attr_accessor :name
end
@errors = ActiveModel::Errors.new(self)
def initialize
extend ActiveModel::Naming
# Required dependency for ActiveModel::Errors
class Person
A minimal implementation could be:
for handling error messages and interacting with Action View helpers.
Provides a modified Hash that you can include in your object
== Active Model Errors

def [](attribute)

person.errors.keys # => [:name]
person.errors[:name] # => []
person.errors.keys # => []

of error keys which includes this attribute.
an empty error list for it and +keys+ will return an array
no errors associated with it, this method will instantiate
Note that, if you try to get errors of an attribute which has

person.errors['name'] # => ["cannot be nil"]
person.errors[:name] # => ["cannot be nil"]

for the method.
When passed a symbol or a name of a method, returns an array of errors 
def [](attribute)
  messages[attribute.to_sym]
end

def add(attribute, message = :invalid, options = {})

# => {:base=>[{error: :name_or_email_blank}]}
person.errors.details
# => {:base=>["either name or email must be present"]}
person.errors.messages
message: "either name or email must be present")
person.errors.add(:base, :name_or_email_blank,

directly associated with a single attribute.
+attribute+ should be set to :base if the error is not

person.errors.messages # => {}

# => NameIsInvalid: Name is invalid
person.errors.add(:name, :invalid, strict: NameIsInvalid)
# => ActiveModel::StrictValidationFailed: Name is invalid
person.errors.add(:name, :invalid, strict: true)

:strict option can also be set to any other exception.
ActiveModel::StrictValidationFailed instead of adding the error.
If the :strict option is set to +true+, it will raise

Time.now to be used within an error.
If +message+ is a proc, it will be called, allowing for things like

scope (see +generate_message+).
If +message+ is a symbol, it will be translated using the appropriate

# => {:name=>[{error: :not_implemented}, {error: :invalid}]}
person.errors.details

# => {:name=>["is invalid", "must be implemented"]}
person.errors.messages

# => ["is invalid", "must be implemented"]
person.errors.add(:name, :not_implemented, message: "must be implemented")
# => ["is invalid"]
person.errors.add(:name)

If no +message+ is supplied, :invalid is assumed.
More than one error can be added to the same +attribute+.
Adds +message+ to the error messages and used validator type to +details+ on +attribute+. 
def add(attribute, message = :invalid, options = {})
  message = message.call if message.respond_to?(:call)
  detail  = normalize_detail(message, options)
  message = normalize_message(attribute, message, options)
  if exception = options[:strict]
    exception = ActiveModel::StrictValidationFailed if exception == true
    raise exception, full_message(attribute, message)
  end
  details[attribute.to_sym]  << detail
  messages[attribute.to_sym] << message
end

def added?(attribute, message = :invalid, options = {})

person.errors.added? :name, "is too long" # => false
person.errors.added? :name, :too_long # => false
person.errors.added? :name, :too_long, count: 24 # => false
person.errors.added? :name, "is too long (maximum is 25 characters)" # => true
person.errors.added? :name, :too_long, count: 25 # => true
person.errors.add :name, :too_long, { count: 25 }

the correct option, or +false+ with an incorrect or missing option.
If the error message requires an option, then it returns +true+ with

person.errors.added? :name, "can't be blank" # => true
person.errors.added? :name, :blank # => true
person.errors.add :name, :blank

present, or +false+ otherwise. +message+ is treated the same as for +add+.
Returns +true+ if an error on the attribute with the given message is 
def added?(attribute, message = :invalid, options = {})
  message = message.call if message.respond_to?(:call)
  message = normalize_message(attribute, message, options)
  self[attribute].include? message
end

def apply_default_array(hash) 

def apply_default_array(hash)
  hash.default_proc = proc { |h, key| h[key] = [] }
  hash
end

def as_json(options = nil)

person.errors.as_json(full_messages: true) # => {:name=>["name cannot be nil"]}
person.errors.as_json # => {:name=>["cannot be nil"]}

if the json object should contain full messages or not (false by default).
object. You can pass the :full_messages option. This determines
Returns a Hash that can be used as the JSON representation for this 
def as_json(options = nil)
  to_hash(options && options[:full_messages])
end

def clear

person.errors.full_messages # => []
person.errors.clear
person.errors.full_messages # => ["name cannot be nil"]

Clear the error messages. 
def clear
  messages.clear
  details.clear
end

def copy!(other) # :nodoc:

:nodoc:
person.errors.copy!(other)

Examples

other - The ActiveModel::Errors instance.

Copies the errors from other. 
def copy!(other) # :nodoc:
  @messages = other.messages.dup
  @details  = other.details.dup
end

def delete(key)

person.errors[:name] # => []
person.errors.delete(:name) # => ["cannot be nil"]
person.errors[:name] # => ["cannot be nil"]

Delete messages for +key+. Returns the deleted messages. 
def delete(key)
  attribute = key.to_sym
  details.delete(attribute)
  messages.delete(attribute)
end

def each

end
# then yield :name and "must be specified"
# Will yield :name and "can't be blank"
person.errors.each do |attribute, error|
person.errors.add(:name, :not_specified, message: "must be specified")

end
# Will yield :name and "can't be blank"
person.errors.each do |attribute, error|
person.errors.add(:name, :blank, message: "can't be blank")

has more than one error message, yields once for each error message.
Yields the attribute and the error for that attribute. If the attribute
Iterates through each error key, value pair in the error messages hash. 
def each
  messages.each_key do |attribute|
    messages[attribute].each { |error| yield attribute, error }
  end
end

def empty?

person.errors.empty? # => false
person.errors.full_messages # => ["name cannot be nil"]

If the error message is a string it can be empty.
Returns +true+ if no errors are found, +false+ otherwise. 
def empty?
  size.zero?
end

def full_message(attribute, message)

person.errors.full_message(:name, 'is invalid') # => "Name is invalid"

Returns a full message for a given attribute. 
def full_message(attribute, message)
  return message if attribute == :base
  attr_name = attribute.to_s.tr(".", "_").humanize
  attr_name = @base.class.human_attribute_name(attribute, default: attr_name)
  I18n.t(:"errors.format",
    default:  "%{attribute} %{message}",
    attribute: attr_name,
    message:   message)
end

def full_messages

# => ["Name is too short (minimum is 5 characters)", "Name can't be blank", "Email can't be blank"]
person.errors.full_messages
person = Person.create(address: '123 First St.')

end
validates_length_of :name, in: 5..30
validates_presence_of :name, :address, :email
class Person

Returns all the full error messages in an array. 
def full_messages
  map { |attribute, message| full_message(attribute, message) }
end

def full_messages_for(attribute)

# => ["Name is too short (minimum is 5 characters)", "Name can't be blank"]
person.errors.full_messages_for(:name)
person = Person.create()

end
validates_length_of :name, in: 5..30
validates_presence_of :name, :email
class Person

Returns all the full error messages for a given attribute in an array. 
def full_messages_for(attribute)
  attribute = attribute.to_sym
  messages[attribute].map { |message| full_message(attribute, message) }
end

def generate_message(attribute, type = :invalid, options = {})

* errors.messages.blank
* errors.attributes.title.blank
* activemodel.errors.messages.blank
* any default you provided through the +options+ hash (in the activemodel.errors scope)
* activemodel.errors.models.user.blank
* activemodel.errors.models.user.attributes.title.blank
* activemodel.errors.models.admin.blank
* activemodel.errors.models.admin.attributes.title.blank

it looks for these translations:
the :blank error message for the title attribute,
class Admin < User; end and you wanted the translation for
models too, but only if the model itself hasn't been found. Say you have
When using inheritance in your models, it will check all the inherited

interpolation.
name, translated attribute name and the value are available for
(e.g. activemodel.errors.messages.MESSAGE). The translated model
that is not there also, it returns the translation of the default message
if it's not there, it's looked up in activemodel.errors.models.MODEL.MESSAGE and if
Error messages are first looked up in activemodel.errors.models.MODEL.attributes.ATTRIBUTE.MESSAGE,

(activemodel.errors.messages).
Translates an error message in its default scope 
def generate_message(attribute, type = :invalid, options = {})
  type = options.delete(:message) if options[:message].is_a?(Symbol)
  if @base.class.respond_to?(:i18n_scope)
    defaults = @base.class.lookup_ancestors.map do |klass|
      [ :"#{@base.class.i18n_scope}.errors.models.#{klass.model_name.i18n_key}.attributes.#{attribute}.#{type}",
        :"#{@base.class.i18n_scope}.errors.models.#{klass.model_name.i18n_key}.#{type}" ]
    end
  else
    defaults = []
  end
  defaults << :"#{@base.class.i18n_scope}.errors.messages.#{type}" if @base.class.respond_to?(:i18n_scope)
  defaults << :"errors.attributes.#{attribute}.#{type}"
  defaults << :"errors.messages.#{type}"
  defaults.compact!
  defaults.flatten!
  key = defaults.shift
  defaults = options.delete(:message) if options[:message]
  value = (attribute != :base ? @base.send(:read_attribute_for_validation, attribute) : nil)
  options = {
    default: defaults,
    model: @base.model_name.human,
    attribute: @base.class.human_attribute_name(attribute),
    value: value,
    object: @base
  }.merge!(options)
  I18n.translate(key, options)
end

def include?(attribute)

person.errors.include?(:age) # => false
person.errors.include?(:name) # => true
person.errors.messages # => {:name=>["cannot be nil"]}

+attribute+, +false+ otherwise.
Returns +true+ if the error messages include an error for the given key 
def include?(attribute)
  attribute = attribute.to_sym
  messages.key?(attribute) && messages[attribute].present?
end

def init_with(coder) # :nodoc:

:nodoc: 
def init_with(coder) # :nodoc:
  coder.map.each { |k, v| instance_variable_set(:"@#{k}", v) }
  @details ||= {}
  apply_default_array(@messages)
  apply_default_array(@details)
end

def initialize(base)

end
end
@errors = ActiveModel::Errors.new(self)
def initialize
class Person

Pass in the instance of the object that is using the errors object. 
def initialize(base)
  @base     = base
  @messages = apply_default_array({})
  @details = apply_default_array({})
end

def initialize_dup(other) # :nodoc:

:nodoc: 
def initialize_dup(other) # :nodoc:
  @messages = other.messages.dup
  @details  = other.details.deep_dup
  super
end

def keys

person.errors.keys # => [:name]
person.errors.messages # => {:name=>["cannot be nil", "must be specified"]}

Returns all message keys. 
def keys
  messages.keys
end

def marshal_dump # :nodoc:

:nodoc: 
def marshal_dump # :nodoc:
  [@base, without_default_proc(@messages), without_default_proc(@details)]
end

def marshal_load(array) # :nodoc:

:nodoc: 
def marshal_load(array) # :nodoc:
  @base, @messages, @details = array
  apply_default_array(@messages)
  apply_default_array(@details)
end

def normalize_detail(message, options) 

def normalize_detail(message, options)
  { error: message }.merge(options.except(*CALLBACKS_OPTIONS + MESSAGE_OPTIONS))
end

def normalize_message(attribute, message, options) 

def normalize_message(attribute, message, options)
  case message
  when Symbol
    generate_message(attribute, message, options.except(*CALLBACKS_OPTIONS))
  else
    message
  end
end

def size

person.errors.size # => 2
person.errors.add(:name, :not_specified, message: "must be specified")
person.errors.size # => 1
person.errors.add(:name, :blank, message: "can't be blank")

Returns the number of error messages. 
def size
  values.flatten.size
end

def to_hash(full_messages = false)

person.errors.to_hash(true) # => {:name=>["name cannot be nil"]}
person.errors.to_hash # => {:name=>["cannot be nil"]}

is +true+, it will contain full messages (see +full_message+).
Returns a Hash of attributes with their error messages. If +full_messages+ 
def to_hash(full_messages = false)
  if full_messages
    messages.each_with_object({}) do |(attribute, array), messages|
      messages[attribute] = array.map { |message| full_message(attribute, message) }
    end
  else
    without_default_proc(messages)
  end
end

def to_xml(options = {})

#
# name must be specified
# name can't be blank
#
#
# =>
person.errors.to_xml
person.errors.add(:name, :not_specified, message: "must be specified")
person.errors.add(:name, :blank, message: "can't be blank")

Returns an xml formatted representation of the Errors hash. 
def to_xml(options = {})
  to_a.to_xml({ root: "errors", skip_types: true }.merge!(options))
end

def values

person.errors.values # => [["cannot be nil", "must be specified"]]
person.errors.messages # => {:name=>["cannot be nil", "must be specified"]}

Returns all message values. 
def values
  messages.values
end

def without_default_proc(hash) 

def without_default_proc(hash)
  hash.dup.tap do |new_h|
    new_h.default_proc = nil
  end
end