Rails 5 has_many_through include pivot table in result - ruby-on-rails

Question

I have a Rails 5 app with restaurants and products. One product has_many restaurant and one restaurant has many products. I created a pivot table and created and has_many_through relation since I want to work with the pivot table.
Product:
has_many :restaurant_products, dependent: :destroy
has_many :restaurants, through: :restaurant_products
Restaurant:
has_many :restaurant_products, dependent: :destroy
has_many :products, through: :restaurant_products
Since every restaurant can modify the price for each product I have added a custom_price column to my restaurant_products table.
Now I can get all products for a certain restaurant:
#restaurant.products
But this way, when I list the products, I don't have access to the custom price. How can I somehow include or access the correct pivot record to get the custom price?

Answer 1

You can use the following:
#restaurant.restaurant_products.joins(:products).select('restaurant_products.custom_price, products.*')
That will give you access to instances including all of a product's columns, as well as the join table's custom price.
The SQL generated will look similar to:
SELECT restaurant_products.custom_price, products.*
FROM `restaurant_products`
INNER JOIN `products` ON `products`.`id` = `restaurant_products`.`product_id`
WHERE `restaurant_products`.`restaurant_id` = 1
Quick tip: what's returned might look a little strange, something like:
[#<RestaurantProduct id: 1, custom_price: 10>]
...though if you call attributes, or a product attribute on an instance here, you'll have access to everything you want.
The above gives quick and efficient access to the records' data, though if you need to access methods on the product itself, you might prefer the following:
#product_details = #restaurant.restaurant_products.includes(:products)
And then to loop through the data:
#product_details.each do |product_detail|
product_detail.custom_price
product_detail.product.column_data
product_detail.product.a_method
end
Hope these help - let me know how you get on or if you have any questions.

Answer 2

Just provide a custom select that includes the row from the join table:
#products = #restaurant.products
.select('products.*, restaurant_products.custom_price')
This returns restaurant_products.custom_price as if it where a column on products. You can us AS to provide a alias if you want to call it something else than custom_price.
So you can do:
<table>
# ...
<% #products.each do |product| %>
<tr>
<td><%= product.name %></td>
<td><%= product.custom_price %></td>
</tr>
<% end %>
</table>

Answer 3

In such cases, it always better to query on pivot table as bellow
#restaurant_products = RestaurantProduct.includes(:product)
.where(restaurant_id: #restaurant.id)
You can display it in the view simply as follows.
<table>
<% #restaurant_products.each do |resta_product| %>
<tr>
<td><%= resta_product.product.name %></td>
<td><%= resta_product.custom_price %></td>
</tr>
<% end %>
</table>
You can even delegate all product methods to work directly on restaurant_product.