def register_model(klass)
      LOCK.synchronize do
        models.push(klass) unless models.include?(klass)
      end
    end
def register_model(klass)
      LOCK.synchronize do
        models.push(klass) unless models.include?(klass)
      end
    end
Register a model in the application with Mongoid.

 @example Register a model.
   config.register_model(Band)

 @param [ Class ] klass The model to register.

 @since 3.1.0