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Active Model Errors

Provides a modified Hash that you can include in your object for handling error messages and interacting with Action View helpers.

A minimal implementation could be:

class Person
  # Required dependency for ActiveModel::Errors
  extend ActiveModel::Naming

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

  attr_accessor :name
  attr_reader   :errors

  def validate!
    errors.add(:name, :blank, message: "cannot be nil") if name.nil?
  end

  # The following methods are needed to be minimally implemented

  def read_attribute_for_validation(attr)
    send(attr)
  end

  def self.human_attribute_name(attr, options = {})
    attr
  end

  def self.lookup_ancestors
    [self]
  end
end

The last three methods are required in your object for Errors to be able to generate error messages correctly and also handle multiple languages. Of course, if you extend your object with ActiveModel::Translation you will not need to implement the last two. Likewise, using ActiveModel::Validations will handle the validation related methods for you.

The above allows you to do:

person = Person.new
person.validate!            # => ["cannot be nil"]
person.errors.full_messages # => ["name cannot be nil"]
# etc..
Methods
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Included Modules
Constants
LEGACY_ATTRIBUTES = [:messages, :details].freeze
 
Attributes
[R] errors
[R] objects
Class Public methods
new(base)

Pass in the instance of the object that is using the errors object.

class Person
  def initialize
    @errors = ActiveModel::Errors.new(self)
  end
end
# File activemodel/lib/active_model/errors.rb, line 82
def initialize(base)
  @base = base
  @errors = []
end
Instance Public methods
[](attribute)

When passed a symbol or a name of a method, returns an array of errors for the method.

person.errors[:name]  # => ["cannot be nil"]
person.errors['name'] # => ["cannot be nil"]
# File activemodel/lib/active_model/errors.rb, line 204
def [](attribute)
  DeprecationHandlingMessageArray.new(messages_for(attribute), self, attribute)
end
add(attribute, type = :invalid, **options)

Adds message to the error messages and used validator type to details on attribute. More than one error can be added to the same attribute. If no message is supplied, :invalid is assumed.

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

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

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

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

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

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

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

person.errors.messages # => {}

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

person.errors.add(:base, :name_or_email_blank,
  message: "either name or email must be present")
person.errors.messages
# => {:base=>["either name or email must be present"]}
person.errors.details
# => {:base=>[{error: :name_or_email_blank}]}
# File activemodel/lib/active_model/errors.rb, line 373
def add(attribute, type = :invalid, **options)
  attribute, type, options = normalize_arguments(attribute, type, **options)
  error = Error.new(@base, attribute, type, **options)

  if exception = options[:strict]
    exception = ActiveModel::StrictValidationFailed if exception == true
    raise exception, error.full_message
  end

  @errors.append(error)

  error
end
added?(attribute, type = :invalid, options = {})

Returns true if an error on the attribute with the given message is present, or false otherwise. message is treated the same as for add.

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

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

person.errors.add :name, :too_long, { count: 25 }
person.errors.added? :name, :too_long, count: 25                     # => true
person.errors.added? :name, "is too long (maximum is 25 characters)" # => true
person.errors.added? :name, :too_long, count: 24                     # => false
person.errors.added? :name, :too_long                                # => false
person.errors.added? :name, "is too long"                            # => false
# File activemodel/lib/active_model/errors.rb, line 403
def added?(attribute, type = :invalid, options = {})
  attribute, type, options = normalize_arguments(attribute, type, **options)

  if type.is_a? Symbol
    @errors.any? { |error|
      error.strict_match?(attribute, type, **options)
    }
  else
    messages_for(attribute).include?(type)
  end
end
as_json(options = nil)

Returns a Hash that can be used as the JSON representation for this object. You can pass the :full_messages option. This determines if the json object should contain full messages or not (false by default).

person.errors.as_json                      # => {:name=>["cannot be nil"]}
person.errors.as_json(full_messages: true) # => {:name=>["name cannot be nil"]}
# File activemodel/lib/active_model/errors.rb, line 288
def as_json(options = nil)
  to_hash(options && options[:full_messages])
end
delete(attribute, type = nil, **options)

Delete messages for key. Returns the deleted messages.

person.errors[:name]        # => ["cannot be nil"]
person.errors.delete(:name) # => ["cannot be nil"]
person.errors[:name]        # => []
# File activemodel/lib/active_model/errors.rb, line 190
def delete(attribute, type = nil, **options)
  attribute, type, options = normalize_arguments(attribute, type, **options)
  matches = where(attribute, type, **options)
  matches.each do |error|
    @errors.delete(error)
  end
  matches.map(&:message).presence
end
details()
# File activemodel/lib/active_model/errors.rb, line 320
def details
  hash = {}
  group_by_attribute.each do |attribute, errors|
    hash[attribute] = errors.map(&:detail)
  end
  DeprecationHandlingDetailsHash.new(hash)
end
each(&block)

Iterates through each error key, value pair in the error messages hash. Yields the attribute and the error for that attribute. If the attribute has more than one error message, yields once for each error message.

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

person.errors.add(:name, :not_specified, message: "must be specified")
person.errors.each do |attribute, error|
  # Will yield :name and "can't be blank"
  # then yield :name and "must be specified"
end
# File activemodel/lib/active_model/errors.rb, line 222
    def each(&block)
      if block.arity <= 1
        @errors.each(&block)
      else
        ActiveSupport::Deprecation.warn(<<~MSG)
          Enumerating ActiveModel::Errors as a hash has been deprecated.
          In Rails 6.1, `errors` is an array of Error objects,
          therefore it should be accessed by a block with a single block
          parameter like this:

          person.errors.each do |error|
            error.full_message
          end

          You are passing a block expecting two parameters,
          so the old hash behavior is simulated. As this is deprecated,
          this will result in an ArgumentError in Rails 6.2.
        MSG
        @errors.
          sort { |a, b| a.attribute <=> b.attribute }.
          each { |error| yield error.attribute, error.message }
      end
    end
full_message(attribute, message)

Returns a full message for a given attribute.

person.errors.full_message(:name, 'is invalid') # => "Name is invalid"
# File activemodel/lib/active_model/errors.rb, line 472
def full_message(attribute, message)
  Error.full_message(attribute, message, @base.class)
end
full_messages()

Returns all the full error messages in an array.

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

person = Person.create(address: '123 First St.')
person.errors.full_messages
# => ["Name is too short (minimum is 5 characters)", "Name can't be blank", "Email can't be blank"]
Also aliased as: to_a
# File activemodel/lib/active_model/errors.rb, line 446
def full_messages
  @errors.map(&:full_message)
end
full_messages_for(attribute)

Returns all the full error messages for a given attribute in an array.

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

person = Person.create()
person.errors.full_messages_for(:name)
# => ["Name is too short (minimum is 5 characters)", "Name can't be blank"]
# File activemodel/lib/active_model/errors.rb, line 461
def full_messages_for(attribute)
  where(attribute).map(&:full_message).freeze
end
generate_message(attribute, type = :invalid, options = {})

Translates an error message in its default scope (activemodel.errors.messages).

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

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

  • activemodel.errors.models.admin.attributes.title.blank

  • activemodel.errors.models.admin.blank

  • activemodel.errors.models.user.attributes.title.blank

  • activemodel.errors.models.user.blank

  • any default you provided through the options hash (in the activemodel.errors scope)

  • activemodel.errors.messages.blank

  • errors.attributes.title.blank

  • errors.messages.blank

# File activemodel/lib/active_model/errors.rb, line 500
def generate_message(attribute, type = :invalid, options = {})
  Error.generate_message(attribute, type, @base, options)
end
group_by_attribute()
# File activemodel/lib/active_model/errors.rb, line 328
def group_by_attribute
  @errors.group_by(&:attribute)
end
has_key?(attribute)
Alias for: include?
import(error, override_options = {})

Imports one error Imported errors are wrapped as a NestedError, providing access to original error object. If attribute or type needs to be overridden, use `override_options`.

override_options - Hash @option override_options [Symbol] :attribute Override the attribute the error belongs to @option override_options [Symbol] :type Override type of the error.

# File activemodel/lib/active_model/errors.rb, line 115
def import(error, override_options = {})
  [:attribute, :type].each do |key|
    if override_options.key?(key)
      override_options[key] = override_options[key].to_sym
    end
  end
  @errors.append(NestedError.new(@base, error, override_options))
end
include?(attribute)

Returns true if the error messages include an error for the given key attribute, false otherwise.

person.errors.messages        # => {:name=>["cannot be nil"]}
person.errors.include?(:name) # => true
person.errors.include?(:age)  # => false
Also aliased as: has_key?, key?
# File activemodel/lib/active_model/errors.rb, line 177
def include?(attribute)
  @errors.any? { |error|
    error.match?(attribute.to_sym)
  }
end
key?(attribute)
Alias for: include?
keys()

Returns all message keys.

person.errors.messages # => {:name=>["cannot be nil", "must be specified"]}
person.errors.keys     # => [:name]
# File activemodel/lib/active_model/errors.rb, line 259
def keys
  deprecation_removal_warning(:keys)
  keys = @errors.map(&:attribute)
  keys.uniq!
  keys.freeze
end
merge!(other)

Merges the errors from other, each Error wrapped as NestedError.

other - The ActiveModel::Errors instance.

Examples

person.errors.merge!(other)
# File activemodel/lib/active_model/errors.rb, line 132
def merge!(other)
  other.errors.each { |error|
    import(error)
  }
end
messages()
# File activemodel/lib/active_model/errors.rb, line 316
def messages
  DeprecationHandlingMessageHash.new(self)
end
messages_for(attribute)
# File activemodel/lib/active_model/errors.rb, line 465
def messages_for(attribute)
  where(attribute).map(&:message)
end
of_kind?(attribute, message = :invalid)

Returns true if an error on the attribute with the given message is present, or false otherwise. message is treated the same as for add.

person.errors.add :age
person.errors.add :name, :too_long, { count: 25 }
person.errors.of_kind? :age                                            # => true
person.errors.of_kind? :name                                           # => false
person.errors.of_kind? :name, :too_long                                # => true
person.errors.of_kind? :name, "is too long (maximum is 25 characters)" # => true
person.errors.of_kind? :name, :not_too_long                            # => false
person.errors.of_kind? :name, "is too long"                            # => false
# File activemodel/lib/active_model/errors.rb, line 426
def of_kind?(attribute, message = :invalid)
  attribute, message = normalize_arguments(attribute, message)

  if message.is_a? Symbol
    !where(attribute, message).empty?
  else
    messages_for(attribute).include?(message)
  end
end
slice!(*keys)

Removes all errors except the given keys. Returns a hash containing the removed errors.

person.errors.keys                  # => [:name, :age, :gender, :city]
person.errors.slice!(:age, :gender) # => { :name=>["cannot be nil"], :city=>["cannot be nil"] }
person.errors.keys                  # => [:age, :gender]
# File activemodel/lib/active_model/errors.rb, line 143
def slice!(*keys)
  deprecation_removal_warning(:slice!)

  keys = keys.map(&:to_sym)

  results = messages.dup.slice!(*keys)

  @errors.keep_if do |error|
    keys.include?(error.attribute)
  end

  results
end
to_a()
Alias for: full_messages
to_h()
# File activemodel/lib/active_model/errors.rb, line 306
    def to_h
      ActiveSupport::Deprecation.warn(<<~EOM)
        ActiveModel::Errors#to_h is deprecated and will be removed in Rails 6.2
        Please use `ActiveModel::Errors.to_hash` instead. The values in the hash
        returned by `ActiveModel::Errors.to_hash` is an array of error messages.
      EOM

      to_hash.transform_values { |values| values.last }
    end
to_hash(full_messages = false)

Returns a Hash of attributes with their error messages. If full_messages is true, it will contain full messages (see full_message).

person.errors.to_hash       # => {:name=>["cannot be nil"]}
person.errors.to_hash(true) # => {:name=>["name cannot be nil"]}
# File activemodel/lib/active_model/errors.rb, line 297
def to_hash(full_messages = false)
  hash = {}
  message_method = full_messages ? :full_message : :message
  group_by_attribute.each do |attribute, errors|
    hash[attribute] = errors.map(&message_method)
  end
  hash
end
to_xml(options = {})

Returns an xml formatted representation of the Errors hash.

person.errors.add(:name, :blank, message: "can't be blank")
person.errors.add(:name, :not_specified, message: "must be specified")
person.errors.to_xml
# =>
#  <?xml version=\"1.0\" encoding=\"UTF-8\"?>
#  <errors>
#    <error>name can't be blank</error>
#    <error>name must be specified</error>
#  </errors>
# File activemodel/lib/active_model/errors.rb, line 277
def to_xml(options = {})
  deprecation_removal_warning(:to_xml)
  to_a.to_xml({ root: "errors", skip_types: true }.merge!(options))
end
values()

Returns all message values.

person.errors.messages # => {:name=>["cannot be nil", "must be specified"]}
person.errors.values   # => [["cannot be nil", "must be specified"]]
# File activemodel/lib/active_model/errors.rb, line 250
def values
  deprecation_removal_warning(:values)
  @errors.map(&:message).freeze
end
where(attribute, type = nil, **options)

Search for errors matching attribute, type or options.

Only supplied params will be matched.

person.errors.where(:name) # => all name errors.
person.errors.where(:name, :too_short) # => all name errors being too short
person.errors.where(:name, :too_short, minimum: 2) # => all name errors being too short and minimum is 2
# File activemodel/lib/active_model/errors.rb, line 164
def where(attribute, type = nil, **options)
  attribute, type, options = normalize_arguments(attribute, type, **options)
  @errors.select { |error|
    error.match?(attribute, type, **options)
  }
end