A simple base class that can be used along with ActiveModel::Validations::ClassMethods.validates_with
class Person include ActiveModel::Validations validates_with MyValidator end class MyValidator < ActiveModel::Validator def validate(record) if some_complex_logic record.errors[:base] = "This record is invalid" end end private def some_complex_logic # ... end end
Any class that inherits from ActiveModel::Validator must implement a method called validate which accepts a record.
class Person include ActiveModel::Validations validates_with MyValidator end class MyValidator < ActiveModel::Validator def validate(record) record # => The person instance being validated options # => Any non-standard options passed to validates_with end end
To cause a validation error, you must add to the record‘s errors directly from within the validators message
class MyValidator < ActiveModel::Validator def validate(record) record.errors[:base] << "This is some custom error message" record.errors[:first_name] << "This is some complex validation" # etc... end end
To add behavior to the initialize method, use the following signature:
class MyValidator < ActiveModel::Validator def initialize(record, options) super @my_custom_field = options[:field_name] || :first_name end end
The easiest way to add custom validators for validating individual attributes is with the convenient ActiveModel::EachValidator. For example:
class TitleValidator < ActiveModel::EachValidator def validate_each(record, attribute, value) record.errors[attribute] << 'must be Mr. Mrs. or Dr.' unless value.in?(['Mr.', 'Mrs.', 'Dr.']) end end
This can now be used in combination with the validates method (see ActiveModel::Validations::ClassMethods.validates for more on this)
class Person include ActiveModel::Validations attr_accessor :title validates :title, :presence => true end
Validator may also define a setup instance method which will get called with the class that using that validator as its argument. This can be useful when there are prerequisites such as an attr_accessor being present for example:
class MyValidator < ActiveModel::Validator def setup(klass) klass.send :attr_accessor, :custom_attribute end end
This setup method is only called when used with validation macros or the class level validates_with method.
Returns the kind of the validator. Examples:
PresenceValidator.kind # => :presence UniquenessValidator.kind # => :uniqueness
# File lib/active_model/validator.rb, line 107 def self.kind @kind ||= name.split('::').last.underscore.sub(/_validator$/, '').to_sym unless anonymous? end
Return the kind for this validator.
# File lib/active_model/validator.rb, line 117 def kind self.class.kind end
Override this method in subclasses with validation logic, adding errors to the records errors array where necessary.
# File lib/active_model/validator.rb, line 123 def validate(record) raise NotImplementedError, "Subclasses must implement a validate(record) method." end
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