Question

I’m working on a small DataMapper-like ODM project, and I’m trying to make use of the ActiveModel::Validations component. However, I ran into a problem while writing tests – I’m using anonymous classes to construct my test schemas, however when it comes to running the validators, the ActiveModel::Name class is throwing an error:
Class name cannot be blank. You need to supply a name argument when anonymous class given

Here’s a simple code example to reproduce:

require 'active_model'

book_class = Class.new do
  include ActiveModel::Validations

  validates_presence_of :title

  def title; ""; end # This will fail validation
end

book_class.new.valid? # => throws error

The exception is only raised when there’s a failed validator – I’m guessing the problem happens when it tries to construct the validation error message. So my question is:

• I did a lot of searching, but couldn’t find anyone trying to do something similar. Is this simply not possible with ActiveModel, or is there a workaround I’m not aware of?

Answer 1

ActiveModel tries to get the model name (as you see here) when setting up the error messages. The quickest way to get around it (short of giving your anonymous class a name), is to give your class a class method model_name that returns an instance of ActiveModel::Name.

for example

require 'active_model'

book_class = Class.new do
  include ActiveModel::Validations
  def self.model_name
    ActiveModel::Name.new(self, nil, "temp")
  end
  validates_presence_of :title

  def title; ""; end # This will fail validation
end

book_class.new.valid? # => no error