I found an interesting thing that it seems the model object does not need to specify 'require' method at the beginning, for example:
I can directly use the model object in a class in a different folder, either in a controller class or another model object, I haven't try it on the erb view file yet.
But for other regular ruby class file, I have to specify the 'require' statement at the beginning.
For controller, I found if I want to inside one controller to call another controller's method, I have to specify 'require some_model/some_controller'.
Why is the model object so special, can anybody explain the mechanism to me?