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

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

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"]

Adds a new error of type on attribute. More than one error can be added to the same attribute. If no type is supplied, :invalid is assumed.

person.errors.add(:name)
# Adds <#ActiveModel::Error attribute=name, type=invalid>
person.errors.add(:name, :not_implemented, message: "must be implemented")
# Adds <#ActiveModel::Error attribute=name, type=not_implemented,
                            options={:message=>"must be implemented"}>

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

If type is a string, it will be used as error message.

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

person.errors.add(:name, :blank)
person.errors.messages
# => {:name=>["can't be blank"]}

person.errors.add(:name, :too_long, count: 25)
person.errors.messages
# => ["is too long (maximum is 25 characters)"]

If type 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}]}

Returns true if an error matches provided attribute and type, or false otherwise. type 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 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

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"]}

Returns all error attribute names

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

Delete messages for key. Returns the deleted messages.

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

Returns a Hash of attributes with an array of their error details.

Returns a full message for a given attribute.

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

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"]

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"]

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

Returns a Hash of attributes with an array of their Error objects.

person.errors.group_by_attribute
# => {:name=>[<#ActiveModel::Error>, <#ActiveModel::Error>]}

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.

Options

• :attribute - Override the attribute the error belongs to.

• :type - Override type of the error.

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

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

Parameters

• other - The ActiveModel::Errors instance.

Examples

person.errors.merge!(other)

Returns a Hash of attributes with an array of their error messages.

Returns all the 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.messages_for(:name)
# => ["is too short (minimum is 5 characters)", "can't be blank"]

Returns true if an error on the attribute with the given type is present, or false otherwise. type 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

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"]}

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