Strong params issue in rails 6 - ruby-on-rails

Question

I have a many-to-many model ProductCategory product_category (joint-table) and
I'm having issue with nesting the parameter in the ProductsController. The error I keep getting is that its unpermitted params category_ids but I have nested it in the strong product params.
I took a picture of the important parts of the code. Please take a look and let me know thank you. Here is the most important part of the code I think:
<%= form_with(model: [:user, #product], local: true) do |f|%>
<h4>Category</h4>
<div class="dropdown-trigger btn">
<%= f.collection_select(:category_ids, Category.all, :id, :name) %>
</div>
<h4>Product Name:</h4>
<%= f.text_field :name %><br/>
<h4>Product Price:</h4>
<%= f.number_field :price, value: #product.price ? '%.2f' % #product.price : nil, min: 0, step: 0.01 %>$<br/>
<h4>Product Description:</h4>
<%= f.text_field :description %><br/>
<h4>Product Image (recommended)</h4>
<%= f.file_field :image %><br/>
The require in ProductsController:
def product_params
params.require(:product).permit(:name, :price, :description, :image, category_ids: [])
end
And the relevant parts of Product and ProductCategory model.
class Product < ApplicationRecord
belongs_to :user
has_many :product_categories
has_many :categories, though: :product_categories
has_one_attached :image
end
class ProductCategory < ApplicationRecord
belongs_to :product
belongs_to :category
end
class Category < ApplicationRecord
belongs_to :user
has_many :product_categories
has_many :products, though: :product_categories
end
code screenshot

Answer 1

You are receiving an "unpermitted params category_ids" error, because you first need to declare in your Product model the following:
accepts_nested_attributes_for :categories , allow_destroy: true
Once that is done, you should start receiving all the category_ids info, really nested inside your params.
However, I fully recommend DO NOT perform on your views and partials an ActiveRecord query over your DB. For example:
<div class="dropdown-trigger btn">
<%= f.collection_select(:category_ids, Category.all, :id, :name) %>
</div>
That is not advisable. Instead, you should receive from your controller the whole set of categories. The only function on the view in this case is to fill the data by the user, to select the categories, and then after a submit to send all that information back to the controller. That's all. Not performing any kind of query. It's true that you can do it. I mean, it is physically possible to do it there on that view, or even to do it on a helper (also wrong, a helper is to perform additional actions over resources already loaded or received from controllers), but MVC means the separation of duties for several reasons.
Anyway, in your case I would choose to go more or less with something like this:
On products_controller.rb:
def edit
#categories_to_assign = product_service.get_categories_to_assign(#product)
end
def product_service
ProductService
end
def product_params
params.require(:product).permit(:name, :price, :description, :image, categories_to_assign: [])
end
On product_service.rb it gets the categories:
def self.get_categories_to_assign(product)
categories_scope.where.not(id: product.categories.map(&:id)).map do |category|
["#{category.name}", category.id]
end
end
def self.categories_scope()
Category
end
Then on the edit/new view:
<%
categories_to_assign = #categories_to_assign || []
%>
<% content_for :products_main_content do %>
<div id="edit_product_content">
<%= render partial: 'products/form', locals: {
product: product,
return_to: return_to,
categories_to_assign: categories_to_assign
} %>
</div>
<% end %>
Then on the _form.html.erb partial:
<%
categories_to_assign = local_assigns.fetch(:categories_to_assign, [])
%>
<div class="panel panel-default">
<div class="panel-heading">
<h2 class="panel-title"><%= t('products.categories.title') %></h2>
</div>
<div class="panel-body">
<div class="form-horizontal" id="categories_container" data-sjr-placeholder>
<%= render partial: 'products/categories', locals: {f: f, categories_to_assign: categories_to_assign} %>
</div>
</div>
</div>
And finally on the _categories.html.erb partial:
<%
categories_to_assign = local_assigns.fetch(:categories_to_assign, [])
%>
<% if categories_to_assign.present? %>
<%= select_tag "#{f.object_name}[categories_to_assign][]", options_for_select(categories_to_assign), {id: "#{f.object_name}_categories_to_assign", include_blank: true, multiple: true, class: 'form-control', data: {placeholder: t('products.form.select_category')}} %>
<% end %>
As you can see, the general idea is passing the pertinent information from the controller, after been properly retrieved on the product_service (you should add it), and then it goes to the edit/new view and then it finally goes down into the nested partials. That way everything is separated in its respective areas of responsibilities.