Create 3rd level child in a single form - Rails 5 - ruby-on-rails

Question

I'm building a simple top-to-bottom Workout Routine app on ROR. I'm able to create a Workout Day (parent) and an Exercise (child) on the same form. But I can't seem to save the Weighted Set (grandchild) when I submit the form. The interesting thing is that since the Exercise is saved, I can go to that exercise edit page, add a Weighted Set, and the Weighted Set will show up in the Workout Day show page. I think it has to do with the Weighted Set not being associated with the Exercise at the time of creation. How cam I tie wll three models together? I know I'm close!
I have the whole app on github. I the link isn't working, try this URL https://github.com/j-acosta/routine/tree/association
Models
class WorkoutDay < ApplicationRecord
has_many :exercises, dependent: :destroy
has_many :weighted_sets, through: :exercises
accepts_nested_attributes_for :exercises
accepts_nested_attributes_for :weighted_sets
end
class Exercise < ApplicationRecord
belongs_to :workout_day, optional: true
has_many :weighted_sets, dependent: :destroy
accepts_nested_attributes_for :weighted_sets
end
class WeightedSet < ApplicationRecord
belongs_to :exercise, optional: true
end
Workout Day Controller
class WorkoutDaysController < ApplicationController
before_action :set_workout_day, only: [:show, :edit, :update, :destroy]
...
# GET /workout_days/new
def new
#workout_day = WorkoutDay.new
# has_many association .build method => #parent.child.build
#workout_day.exercises.build
# has_many :through association .build method => #parent.through_child.build
# #workout_day.weighted_sets.build
#workout_day.weighted_sets.build
end
...
# POST /workout_days
# POST /workout_days.json
def create
#workout_day = WorkoutDay.new(workout_day_params)
respond_to do |format|
if #workout_day.save
format.html { redirect_to #workout_day, notice: 'Workout day was successfully created.' }
format.json { render :show, status: :created, location: #workout_day }
else
format.html { render :new }
format.json { render json: #workout_day.errors, status: :unprocessable_entity }
end
end
end
...
private
# Use callbacks to share common setup or constraints between actions.
def set_workout_day
#workout_day = WorkoutDay.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def workout_day_params
params.require(:workout_day).permit(:title, exercises_attributes: [:title, :_destroy, weighted_sets_attributes: [:id, :weight, :repetition]])
end
end
New Workout Day form
<%= form_for #workout_day do |workout_day_form| %>
<% if workout_day.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(workout_day.errors.count, "error") %> prohibited this workout_day from being saved:</h2>
<ul>
<% workout_day.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div>
<%= workout_day_form.label :title, 'Workout Day Name' %>
<%= workout_day_form.text_field :title %>
</div>
exercise_field will go here
<div>
<%= workout_day_form.fields_for :exercises do |exercise_field| %>
<%= exercise_field.label :title, 'Exercise' %>
<%= exercise_field.text_field :title %>
<% end %>
</div>
weighted_set_fields will go here
<div>
<%= workout_day_form.fields_for :weighted_sets do |set| %>
<%= render 'exercises/weighted_set_fields', f: set %>
<% end %>
</div>
<div>
<%= workout_day_form.submit %>
</div>
<% end %>

Answer 1

The culprit is the workout_day_params. In the form you have the fields of weighted_sets nested under the workout_day. But in the workout_day_params, you have weighted_sets_attributes under exercises_attributes which is the reason for your problem. Changing it to below should solve the issue.
def workout_day_params
params.require(:workout_day).permit(:title, exercises_attributes: [:title, :_destroy], weighted_sets_attributes: [:id, :weight, :repetition])
end
ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrMany‌​Reflection
This due to wrong associations. You should consider tweaking your associations like below
class WorkoutDay < ApplicationRecord
has_many :weighted_sets, dependent: :destroy
has_many :exercises, through: :weighted_sets
accepts_nested_attributes_for :exercises
accepts_nested_attributes_for :weighted_sets
end
class Exercise < ApplicationRecord
has_many :weighted_sets, dependent: :destroy
has_many :workout_days, through: :weighted_sets
end
class WeightedSet < ApplicationRecord
belongs_to :exercise, optional: true
belongs_to :workout_day, optional: true
end