rails Calculation (price * quantity) - ruby-on-rails

Question

Hi Im creating an ec site in my rails.
My migration:
(Item) has :name and :price.
(Basket_Item) has :item_id(fk), :basket_id(fk) and :quantity.
The system User will add some items to their basket.
So Basket_items is JOIN Table between (Item) and (Basket)
see like below.
What I want to do:
Get a price of Item and get a quantity from Basket_Items which is selected by user. Then I want to create #total_price = item_price * item_quantity.
Can anyone help me to create the #total_price please.
This is my a try code but it doesn't work on rails console.
Basket_items
class CreateBasketItems < ActiveRecord::Migration[5.2]
def change
create_table :basket_items do |t|
t.references :basket, index: true, null: false, foreign_key: true
t.references :item, index: true, null: false, foreign_key: true
t.integer :quantity, null: false, default: 1
t.timestamps
end
end
end
///
Items
class CreateItems < ActiveRecord::Migration[5.2]
def change
create_table :items do |t|
t.references :admin, index: true, null: false, foreign_key: true
t.string :name, null: false, index: true
t.integer :price, null: false
t.text :message
t.string :category, index: true
t.string :img
t.string :Video_url
t.text :discription
t.timestamps
end
end
end
///
This is my try a code but it doesn't work on rails console.
basket = current_user.prepare_basket
item_ids = basket.basket_items.select(:item_id)
items = basket.items.where(id: item_ids)
items_price = items.select(:price)
items_quantity = basket.basket_items.where(item_id: item_ids).pluck(:quantity)
def self.total(items_price, items_quantity)
sum(items_price * items_quantity)
end
#total_price = basket.total(items_price, item_quantity)

Answer 1

There are a few issues with your code:
You are trying to call a class method on an instance of the class. That's not gonna work, second you are passing in arrays into the calculation.
basket = current_user.prepare_basket
item_ids = basket.basket_items.select(:item_id)
items = basket.items.where(id: item_ids)
items_price = items.select(:price) # => Array of prices from the items in the basket
items_quantity = basket.basket_items.where(item_id: item_ids).pluck(:quantity) # => Array of quantities from the items in the basket
def self.total(items_price, items_quantity)
sum(items_price * items_quantity) # => So this line will do: sum(['12,95', '9.99'] * [1, 3])
end
#total_price = basket.total(items_price, item_quantity)
As you can see, that ain't gonna work. First you need to change the method and remove the self.
def total(items_price, items_quantity)
# ...
end
Now you can call the total method on a basket object: basket.total(items_price, items_quantity)
And inside the total method you need to loop through each items to do the calculation and add all the results.
def total(items_price, items_quantity)
total_price = 0
items_price.each_with_index do |price, index|
total_price += price * items_quantity[index]
end
total_price
end
But this solution could also fail, because you don't know sure that the order in the items_price is matching with the order of items_quantity. So a better approach would be to do the calculation for each basket_item seperate.
# Basket model
def total
total_price = 0
basket_items.each do |basket_item|
total_price += basket_item.total_price
end
total_price
end
# BasketItem model
def total_price
quantity * item.price
end
Now you can call it like this: basket.total