Question

In a Rails 3.1 project, I have a model class with a custom validator:

class Car < ActiveRecord::Base
  validate :road_must_exist_nearby, :on => :create

  # ...

  def not_a_validator_method
    Road.exists_nearby?
  end

  def road_must_exist_nearby
    if !Road.exists_nearby?
      # ...
    end
  end
end

When I attempt to save my instance of Car …

> car = Car.new
> car.save

I get the following error:

NameError: uninitialized constant Car::Road

---

Why does calling Road.exists_nearby? from a normal instance method work?:

> car.not_a_validator_method
=> true

And why does calling it from a validator method raise an error, as though Rails believes Road should be called through Car?:

> car.road_must_exist_nearby
NameError: uninitialized constant Car::Road

And how can I make the validator method work?

Answer 1

I’m only guessing, but I’d say it’s a namespace/scope issue. Rails is interpreting the “Road” constant as existing in the scope of Car (ie Car::Road). You can probably get around it by referencing the global namespace using: “::Road”