Rails many to many model with select in the view - ruby-on-rails

Question

The logic in the exercise is create a Bill where a Bill have a list of Products with an amount of them.
I have the next 3 models:
Bill
Product
BillItem (This is the intermediate model between Bill and Product for the many to many relationship)
Schema for more clarity:
create_table "bill_items", force: :cascade do |t|
t.integer "amount"
t.integer "product_id"
t.integer "bill_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.index ["bill_id"], name: "index_bill_items_on_bill_id"
t.index ["product_id"], name: "index_bill_items_on_product_id"
end
create_table "bills", force: :cascade do |t|
t.string "user_name"
t.string "dni"
t.date "expiration"
t.float "sub_total"
t.float "grand_total"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "products", force: :cascade do |t|
t.string "name"
t.string "description"
t.float "price"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
First i have a list of created products in my database.
For my BillController i have a _form.html.erb where i want be capable to create dynamic selects for choose a product and set a amount.
My view is the next:
<%= form_for bill do |f| %>
<div>
<%= f.label :user_name %>
<%= f.text_field :user_name %>
</div>
<div>
<%= f.label :dni %>
<%= f.text_field :dni %>
</div>
<div>
<%= f.label :product %>
<%= f.collection_select :product_ids, Product.all, :id, :name %>
</div>
# Here i should add more selects if the user want to add more products.
<div><%= f.submit %></div>
<% end %>
My problem or my question is: how to "groupe" the ids of the products and the amount of them. And the another question is, i can create the other selects dynamically with JS?

Answer 1

You need to be adding multiple BillItem to your form to account for the amount and the product. This is done through accepts_nested_attributes_for on the model. For example:
class Bill < ActiveRecord::Base
has_many :bill_items
accepts_nested_attributes_for :bill_items
end
Initialize a BillItem on the Bill in your controller:
class BillsController < ActionController::Base
def new
#bill = Bill.new
#bill.bill_items.build
end
end
Then in your form, use the fields_for helper to create sub-forms:
<%= form_for #bill do |f| %>
<div>
<%= f.label :user_name %>
<%= f.text_field :user_name %>
</div>
<div>
<%= f.label :dni %>
<%= f.text_field :dni %>
</div>
<%= f.fields_for :bill_items do |f| %>
<div>
<%= f.label :product %>
<%= f.collection_select :product_id, Product.all, :id, :name %>
</div>
<div>
<%= f.label :amount %>
<%= f.number_field :amount %>
</div>
<% end %>
<%= f.submit %></div>
<% end %>
And yes, you can use javascript to create new nested forms.