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

Where are you getting type from?

type is a keyword reserved by Active Record. If you're using STI on your models it gets automatically set with the class name of the object.

For more check out the section Single Table Inheritance here: http://api.rubyonrails.org/classes/ActiveRecord/Base.html#label-Single+table+inheritance

For multipart product names (like in my case CoreProduct, AddonProduct...) adding an underscore
call is needed to get the model name to the right format.

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

If the list gets too long I took an approach where I defined the permitted attributes in every model

# products_controller.rb
def product_class
 @product_class ||= params[:product][:type].camelcase.constantize
end
def create
  product_class.new product_params
end

def product_params
  @product_params ||= product_class.permitted_attributes_from_params(params[:product])
end

# product/product_a.rb 
class ProductA < Product
 def self.permitted_attributes_from_params(params)
  parameters = ActionController::Parameters.new(params)

  parameters.permit(:name, :price).tap do |whitelisted|
    whitelisted[:hash_attribute] = params[:hash_attribute] # this is in case the hash keys are dynamic
  end
 end
end

Again, this approach is for when the possible amount of permitted gets crazy big cause of STI.

Thank you this worked wonderfully!

Just stumbled upon this and found a handy solution for my problem, thank you :)

Thanks! To get the name of the model used in the parameters, you can also use:
@model_instance.model_name.param_key

And what about that?

def user_params
    type = @user.type.underscore.to_sym
    params.require(type).permit(:name, :age)
end

Thanks! To get the name of the model used in the parameters, you can also use:
@model_instance.model_name.param_key

👍 - cleanest IMO. Thanks @flavio-b!