Rails REST API - Generate permitted fields for json input based on model's nested associations without hardcoding attributes

Question

I'm developing a REST Api for an app's factory generators to allow model instances to be also be created using REST, and I'm wondering how can I permit the nested attributes of the model without hardcoding the attributes.

Suppose I have a model called Restaurant

class Restaurant < ApplicationRecord
  has_one :cost, dependent: :destroy, inverse_of: :grant
  has_one :address, dependent: :destroy, inverse_of: :grant
  has_one :owner, dependent: :destroy, inverse_of: :grant

  accepts_nested_attributes_for :cost, :address, :owner
  ...

where its associations also have its own model attributes, and a factory

FactoryGirl.define do factory :restaurant, class Restaurant do

  after(:create) do |restaurant|
    restaurant.cost = assign_attributes(attributse_for(:cost_factory))
    restuarnat.address = assign_attributes(attributes_for(:address_factory))
    restaurant.owner = assign_attributes(attributes_for(:owner_factory))
  end
 ...
end

where its nested associations also have its own factory. I am passing a json body through REST api in this format

{
  "restaurant": {
    "cost_attributes": {
     "staff": 123
     "tables": 123
    }
}

I know I can permit the attributes these way

params.permit(:restaurant)
      .permit(cost_attributes: [:staff, :tables],
              address_attributes: [:address_attr_1],
              owner_attributes: [:owner_attr_1]]

but the actual model I'm working on has many associations. It will be painful to hardcode everything. Is there a way i can permit the parameters coming through instead of hardcoding in my controller? Currently this is what im thinking

params.permit(Restaurant.nested_attributes_options.keys)

but obviously this does not work out.

yoones · Accepted Answer · 2018-11-06 14:09:35Z

1

Here's one way to collect nested attribute names:

mod = Restaurant

nested_attributes = mod.nested_attributes_options.keys.each_with_object({}) do |association, hash|
  hash[:"#{association}_attributes"] = association.
                                       to_s.
                                       classify.
                                       constantize.
                                       send(:attribute_names).
                                       map(&:to_sym)
end
params.permit(:restaurant).permit(nested_attributes)

This code is kinda generic, do not hesitate to adapt it to your specific use-case.

edited Nov 6, 2018 at 14:09

answered Nov 6, 2018 at 13:59

yoones

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Comments

houdinisparks · Accepted Answer · 2018-12-02 14:52:12Z

To improve on yoones answer, here is a way to collect all deeply nested attribute names recursively using reflections :

  def get_nested_attributes(model, _attributes = [])

    # base case
    if model.nested_attributes_options.empty?
      nil

    # recurse deeper
    else
      associations_list = model.reflect_on_all_associations(:has_one)
      associations_list = associations_list.push(model.reflect_on_all_associations(:has_many)).flatten

      nested_attributes = associations_list.each_with_object({}) do |association , hash|

        association_model = association.klass.nil? ? association.name.to_s.classify.constantize : association.klass

        # include attributes of association model
        # { _attributes => [attributes_1, attribute_2] }
        attribute_name = :"#{association.name.to_s}_attributes"
        hash[attribute_name] = association_model
                               .send(:attribute_names)
                               .map(&:to_sym)

        # recurse deeper into tree, get the result and append
        # { _attributes => [attributes_1, attribute_2, { } ] }
        result = get_nested_attributes(association_model, hash[attribute_name])
        if !result.nil?
          hash[attribute_name].push(result)
        end
      end
      nested_attributes
    end
  end

model = Restaurant
nested_attributes = get_nested_attributes(model)
params.permit(nested_attributes)

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