Rails examples: Single Table Inheritance (STI), strong parameters, single controller.

users_controller.rb

# Variant 1
def user_params(type)
  params.require(type.to_sym).permit(attributes)
end

# Variant 2
def user_params(type)
  case type
  when "user"
    params.require(:user).permit(user_attributes)
  when "apprentice"
    params.require(:apprentice).permit(apprentice_attributes)
  end
end

# Variant 3
def update
  ...
  if @user.update(send("#{@user.type.underscore.to_sym}_params"))
  ...
end

def user_params
  params.require(:user).permit(attributes)
end

def apprentice_params
  params.require(:apprentice).permit(attributes)
end

# Variant 4
https://github.com/T-Dnzt/sti-with-rails4/blob/master/app/controllers/animals_controller.rb