Rails 4 - Update Join Table Attributes with has_many through - ruby-on-rails-4

Question

This is a follow-up of my question: Rails 4 - Access Join Table Value in views
Now I know how to retrieve join table attributes and show them in view. But still I can't find the right approach to edit and update the attribute.
Models:
class Recipe < ActiveRecord::Base
has_many :recipe_ingredients
has_many :ingredients, through: :recipe_ingredients
end
class Ingredient < ActiveRecord::Base
has_many :recipe_ingredients
has_many :recipes, through: :recipe_ingredients
end
class RecipeIngredient < ActiveRecord::Base
belongs_to :recipe
belongs_to :ingredient
#there is an attribute t.text :amount
end
Recipe#Edit:
...
<%= simple_form_for #recipe do |f| %>
<div class="form-group">
<%= f.input :name, input_html: { class: "form-control"} %>
<%= f.input :description, input_html: { class: "form-control"} %>
<%= f.collection_select(:ingredient_ids, Ingredient.all, :id, :title, {}, {multiple: true}) %>
<!-- reserve for recipe_ingredients.amount -->
</div>
<%= f.submit "Submit", disable_with: 'Submitting...', class: "btn btn-primary"%>
<% end %>
...
As shown above, this is a many-to-many relationship, each recipe may have several ingredients. It works fine and I can choose the right models to associate with (using collection_select). But I have left the work to edit and update join table attributes undone. I have two ideas in my mind:
Make another edit page for editing join model attributes
Ajax? But not quite familiar with
I know the question seems to be trivial, but many solutions are out-dated(Rails 3). Desperate for a Rails 4 solution.
Edit
Intention: I would like to make the creation of Recipe and Ingredient models on their own, which is done. User will see which recipe using the ingredient in Ingredient#show action, which is done also. As to Recipe#show action, there is a slight difference, where user will see which ingredient it is using as well as the amount(join table attribute), which is done in my previous question. The last problem is, I would like to make this attribute editable.

Answer 1

You may want to look into doing nested models combined with the cocoon gem. This will allow you to have a form which updates multiple models at once and it takes care of all the ajax for you. https://github.com/nathanvda/cocoon. I used this gem on a system where the user needed to be able to add one or more answers to a trivia question via dynamic form fields. I think it could work for you as well with giving the user the ability to add one or many RecipeIngredient relations for a recipe. You would be able to add selects dynamically to your form via Cocoon containing a select with the Ingredient model records.