Active Model Validator
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.add :base, "This is some custom error message"
record.errors.add :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(options)
super
@my_custom_field = options[:field_name] || :first_name
end
end
Note that the validator is initialized only once for the whole application life cycle, and not on each validation run.
The easiest way to add custom validators for validating individual
attributes is with the convenient ActiveModel::EachValidator.
class TitleValidator < ActiveModel::EachValidator
def validate_each(record, attribute, value)
record.errors.add attribute, 'must be Mr., Mrs., or Dr.' unless %w(Mr. Mrs. Dr.).include?(value)
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, title: true end
It can be useful to access the class that is using that validator when
there are prerequisites such as an attr_accessor being
present. This class is accessible via +options+ in the
constructor. To setup your validator override the constructor.
class MyValidator < ActiveModel::Validator
def initialize(options={})
super
options[:class].send :attr_accessor, :custom_attribute
end
end