Rails 6 API only doesn't save nested attributes

Question

I have a Rails 6 application that works in API only mode as a backend provider for a mobile app.

I have two models Offer and ServiceContent

class Offer < ApplicationRecord
  belongs_to :user
  has_many :service_contents
  accepts_nested_attributes_for :service_contents, allow_destroy: true

  #..... much more stuff below here
end

class ServiceContent < ApplicationRecord
  belongs_to :offer
end

My OffersController looks like this:

# frozen_string_literal: true

class OffersController < ApplicationController
  before_action :set_offer, only: %i[show update destroy]
  before_action :authenticate_user, only: %i[create show update destroy]

 
  def new
    @offer = Offer.new
    @offer.service_contents.build
  end
  

  # POST /offers
  # POST /offers.json
  def create
    @offer = Offer.new(offer_params)


    if @offer.save
      render :show, status: :created, location: @offer
    else
      render json: @offer.errors, status: :unprocessable_entity
    end
  end

  # PATCH/PUT /offers/1
  # PATCH/PUT /offers/1.json
  def update
    if @offer.update(offer_params)
      render :show, status: :ok, location: @offer
    else
      render json: @offer.errors, status: :unprocessable_entity
    end
  end

  # DELETE /offers/1
  # DELETE /offers/1.json
  def destroy
    @offer.destroy
  end


  private


  # Use callbacks to share common setup or constraints between actions.
  def set_offer
    @offer = Offer.find(params[:id])
  end

  # Never trust parameters from the scary internet, only allow the white list through.
  def offer_params
    params.require(:offer).permit(:id,
                                  :from,
                                  :to,
                                  :departure_datetime,
                                  :return_datetime,
                                  service_contents_attributes: [:name, :icon_id, :data]
                                  )

    # params.fetch(:offer, {})
  end


end

The problem arises when I want to create this through Postman.

My JSON looks like this:

{
    "from": "Maroco, Maroco",
    "to": "Zagreb, Croatia",
    "departure_datetime": "2020-09-05 14:32:45 +0200",
    "user_id": 1,
    "service_contents": [
        {
            "name": "test",
            "icon_id": 1,
            "data": null
        },
        {
            "name": "itd",
            "icon_id": 2,
            "data": 0
        }
    ]
}

I send the data through the POST method, params clearly go through, but ServiceContent is always created as an empty array.

Started POST "/offers/" for ::1 at 2020-09-05 14:52:56 +0200
Processing by OffersController#create as */*
  Parameters: {"from"=>"Maroco, Maroco", "to"=>"Zagreb, Croatia", "departure_datetime"=>"2020-09-05 14:32:45 +0200", "user_id"=>1, "service_contents"=>[{"name"=>"test", "icon_id"=>1, "data"=>nil}, {"name"=>"itd", "icon_id"=>2, "data"=>0}], "offer"=>{"from"=>"Maroco, Maroco", "to"=>"Zagreb, Croatia", "departure_datetime"=>"2020-09-05 14:32:45 +0200", "user_id"=>1}}
  User Load (0.4ms)  SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2  [["id", 1], ["LIMIT", 1]]
  ↳ app/controllers/application_controller.rb:21:in `refresh_bearer_auth_header'
  CACHE User Load (0.0ms)  SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2  [["id", 1], ["LIMIT", 1]]
  ↳ app/controllers/offers_controller.rb:34:in `create'
  TRANSACTION (0.1ms)  BEGIN
  ↳ app/controllers/offers_controller.rb:34:in `create'
  Offer Create (0.6ms)  INSERT INTO "offers" ("from", "to", "departure_datetime", "user_id", "created_at", "updated_at", "offer_type_icon") VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING "id"  [["from", "Maroco, Maroco"], ["to", "Zagreb, Croatia"], ["departure_datetime", "2020-09-05 12:32:45"], ["user_id", 1], ["created_at", "2020-09-05 12:52:56.689955"], ["updated_at", "2020-09-05 12:52:56.689955"], ["offer_type_icon", 2]]
  ↳ app/controllers/offers_controller.rb:34:in `create'
  TRANSACTION (0.9ms)  COMMIT
  ↳ app/controllers/offers_controller.rb:34:in `create'
  Rendering offers/show.json.jbuilder
  ServiceContent Load (0.3ms)  SELECT "service_contents".* FROM "service_contents" WHERE "service_contents"."offer_id" = $1  [["offer_id", 6]]
  ↳ app/views/offers/_offer.json.jbuilder:10
  Rendered offers/_offer.json.jbuilder (Duration: 7.9ms | Allocations: 2087)
  Rendered offers/show.json.jbuilder (Duration: 8.7ms | Allocations: 2234)
Completed 201 Created in 66ms (Views: 10.2ms | ActiveRecord: 19.7ms | Allocations: 19234)

It clearly saves stuff to the DB since I've got the response:

{
    "id": 6,
    "from": "Maroco, Maroco",
    "to": "Zagreb, Croatia",
    "departure_date": "2020-09-05",
    "departure_time": "12:32",
    "offer_type_icon": 2,
    "service_contents": []
}

But as I said, service_contents are always an empty array.

Any help is appreciated.

Answer 1

Ok, I actually found an answer.

Thanks @dbugger for pointing in a good direction.

After checking the jbuilder I figured out that it's not the actual problem.

When sending nested parameters, Rails expects that they will always have _attributes addition to their name -> https://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html

So instead of:

{
    "from": "Maroco, Maroco",
    "to": "Zagreb, Croatia",
    "departure_datetime": "2020-09-05 14:32:45 +0200",
    "user_id": 1,
    "service_contents": [
        {
            "name": "test",
            "icon_id": 1,
            "data": null
        },
        {
            "name": "itd",
            "icon_id": 2,
            "data": 0
        }
    ]
}

this needs to have:

{
    "from": "Maroco, Maroco",
    "to": "Zagreb, Croatia",
    "departure_datetime": "2020-09-05 14:32:45 +0200",
    "user_id": 1,
    "service_contents_attributes": [
        {
            "name": "test",
            "icon_id": 1,
            "data": null
        },
        {
            "name": "itd",
            "icon_id": 2,
            "data": 0
        }
    ]
}

This way it creates stuff normally and saves it to the database.

Hope it will save someone from headache in the future.