MONGOID-5790 MONGOID-5791 Fix error caused by loading a referenced class prematurely

[jamis]

The problem manifested when a class declared an association on a class that hadn't yet been loaded; when the touchable module began adding its functionality, there were a few lines that tried to load the referenced class, e.g.:

class Child
  include Mongoid::Document
  embedded_in :parent
end

class Parent
  include Mongoid::Document
  embeds_many :children
end

This would result in a NameError because the embedded_in association could not find the Parent class at load-time.

I started by checking to see if we could just raise a more informative error in this case, as a stop-gap before spending more time later to actually fix the issue. Imagine my joy when I realized that the entire problem was caused by a few lines of dead-code! By simply deleting the unused code, the problem went away. 🎉

Edit: a bit more explanation here, after I went through and triple checked the logic. An Association has a klass, which is the class that the association references directly. In the above example, the Child#parent association would have Parent as the klass. An Association also has an inverse_class, which is the class that the association belongs to. Again, to use the Child#parent association as an example, this would be the Child class.

The reason everything "just works", even when the klass references haven't yet been defined, is because the touch behaviors are added to the inverse_class, and not the klass. That is to say, when the Mongoid::Touchable model works its magic in an embedded_in association, it adds the new methods to Child, and not Parent. Ditto for any of the other associations. Thus, it doesn't matter (at load time) whether the klass references exist yet or not, because all we care about are the inverse_class references, which are guaranteed to exist.

[comandeo-mongo]

🥇