Cannot access associated model attributes within a form - ruby-on-rails

Question

I am trying to build a form for a has_many :through relationship. The Problem is, that I can access the attributes from the join table (:through) in the form, but not the other table.
My models look like this:
class Recipe < ActiveRecord::Base
has_many :quantities
has_many :ingredients, through: :quantities
accepts_nested_attributes_for :quantities
end
class Quantity < ActiveRecord::Base
belongs_to :recipe
belongs_to :ingredient
end
class Ingredient < ActiveRecord::Base
has_many :quantities
has_many :recipes, through: :quantities
end
My Form:
<%= form_for(#recipe) do |f| %>
<div class="field">
<%= f.label :title %><br>
<%= f.text_field :title %>
</div>
<div class="field">
<%= f.label :description %><br>
<%= f.text_area :description %>
</div>
<div class="quantities">
<%= f.fields_for :quantities do |builder| %>
<%= render 'quantity_fields', :f => builder%>
<% end %>
<%= link_to_add_association 'Add', f, :quantities %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
And the quantity_fields partial:
<p>
<%= f.label :value, "Value" %>
<%= f.text_field :value %>
<%= f.label :unit, "Unit" %>
<%= f.text_field :unit %>
<%= f.text_field :ingredient %>
<%= f.fields_for :ingredient do |builder|%>
<%= builder.label :name, "Ingredient"%>
<%= builder.text_field :name %>
<% end %>
</p>
The fields for the quantities attributes are correct, but the text field for the ingredient name (within the quantity_fields partial) stays empty.
On the Rails console on the other hand I can easily use the ingredient method on a quantity object and get a result.
I try to find a solution to this since a while now, and it becomes really frustrating to me. I am sure this is a standard task and I am just missing a small part. Can anyone help me?
Edit:
Also when I change my recipe form to directly render the ingredients, it doesn't work. The text fields remain empty.
<%= form_for(#recipe) do |f| %>
<div class="field">
<%= f.label :title %><br>
<%= f.text_field :title %>
</div>
<div class="field">
<%= f.label :description %><br>
<%= f.text_area :description %>
</div>
<div class="ingredients">
<%= f.fields_for :ingredients do |builder| %>
<p>
<%= builder.label :name, "Name" %>
<%= builder.text_field :name %>
<%= builder.label :description, "Description" %>
<%= builder.text_field :description %>
</p>
<% end %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Edit 2:
The recipes controller:
class RecipesController < ApplicationController
before_action :set_recipe, only: [:show, :edit, :update, :destroy]
# GET /recipes
# GET /recipes.json
def index
#recipes = Recipe.all
end
# GET /recipes/1
# GET /recipes/1.json
def show
end
# GET /recipes/new
def new
#recipe = Recipe.new
end
# GET /recipes/1/edit
def edit
end
# POST /recipes
# POST /recipes.json
def create
#recipe = Recipe.new(recipe_params)
respond_to do |format|
if #recipe.save
format.html { redirect_to #recipe, notice: 'Recipe was successfully created.' }
format.json { render :show, status: :created, location: #recipe }
else
format.html { render :new }
format.json { render json: #recipe.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /recipes/1
# PATCH/PUT /recipes/1.json
def update
respond_to do |format|
if #recipe.update(recipe_params)
format.html { redirect_to #recipe, notice: 'Recipe was successfully updated.' }
format.json { render :show, status: :ok, location: #recipe }
else
format.html { render :edit }
format.json { render json: #recipe.errors, status: :unprocessable_entity }
end
end
end
# DELETE /recipes/1
# DELETE /recipes/1.json
def destroy
#recipe.destroy
respond_to do |format|
format.html { redirect_to recipes_url, notice: 'Recipe was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_recipe
#recipe = Recipe.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def recipe_params
params.require(:recipe).permit(:title, :description, quantities_attributes: [:value, :unit, :recipe, :ingredient, :_destroy])
end
end

Answer 1

When utilizing a has_many :through association in that way, you can set up your models like this:
class Recipe < ActiveRecord::Base
has_many :quantities
has_many :ingredients, inverse_of: :recipes
accepts_nested_attributes_for :quantities
end
class Quantity < ActiveRecord::Base
belongs_to :recipe
belongs_to :ingredient
accepts_nested_attributes_for :ingredients
end
class Ingredient < ActiveRecord::Base
has_many :quantities
has_many :recipes, inverse_of: :ingredients
end
This article covers nested attributes with has_many :through associations in a similar context. Hope this helps!