How to calculate totalPrice in sequelize?

Question

I have four tables: Users, Orders, OrderProducts (join table), and Products.

I want to calculate totalprice column in Orders table. OrderProducts has quantity and productId, Products has price column.

Do I need to add price column in OrderProducts table for each item (price * quantity)?

Answer 1

You don't necessarily need to add a price column in the OrderProducts table. You can achieve this by creating a Sequelize association between the tables and using Sequelize's aggregation functions.

Orders.hasMany(OrderProducts);
OrderProducts.belongsTo(Products);

Now, you can calculate the total price dynamically during queries based on the associated data by using the Sequelize's SUM function to multiply the quantity from OrderProducts with the price from Products, resulting in the total price for each order :

const ordersWithTotalPrice = await Orders.findAll({
attributes: [
    'id',
    [sequelize.fn('SUM', sequelize.literal('`OrderProducts`.`quantity` * `Products`.`price`')), 'totalPrice']
],
include: [
    {
        model: OrderProducts,
        attributes: [],
        include: [
            {
                model: Products,
                attributes: []
            }
        ]
    }
],
group: ['Orders.id']
});

console.log(ordersWithTotalPrice);

It is equivalent to executing the following SQL querie:

SELECT 
Orders.id,
SUM(OrderProducts.quantity * Products.price) AS totalPrice
FROM 
Orders
JOIN 
OrderProducts ON Orders.id = OrderProducts.OrderId
JOIN 
Products ON OrderProducts.ProductId = Products.id
GROUP BY 
Orders.id;

This approach ensures that the totalPrice column in the Orders table stays up-to-date without the need for redundant data storage.

Answer 2

You don't necessarily need to add a price column to the OrderProducts table. Instead, you can calculate the total price when needed by joining the necessary tables in a query. Here's a general approach:

1. Database Schema:

• Users (UserId, UserName, ...)
• Orders (OrderId, UserId, TotalPrice, ...)
• OrderProducts (Id, OrderId, ProductId, Quantity, ...)
• Products (ProductId, Price, ...)

2. Query to Calculate Total Price: You can use a query to calculate the total price by joining the Orders, OrderProducts, and Products tables:

SELECT
    O.OrderId,
    O.UserId,
    SUM(OP.Quantity * P.Price) AS TotalPrice
FROM
    Orders O
    JOIN OrderProducts OP ON O.OrderId = OP.OrderId
    JOIN Products P ON OP.ProductId = P.ProductId
GROUP BY
    O.OrderId, O.UserId;

In this query, SUM(OP.Quantity * P.Price) calculates the total price for each order by multiplying the quantity from OrderProducts with the corresponding product price from the Products table.

By organizing your data this way, you avoid redundancy and ensure that the total price is always calculated based on the current product prices. If the price of a product changes, the total price for historical orders will still reflect the correct value.

3. Updating Total Price in Orders Table: If you want to store the total price in the Orders table for quick retrieval, you can update it using the calculated values:

UPDATE Orders O
SET TotalPrice = (
    SELECT SUM(OP.Quantity * P.Price)
    FROM OrderProducts OP
        JOIN Products P ON OP.ProductId = P.ProductId
    WHERE O.OrderId = OP.OrderId
);

This query updates the TotalPrice column in the Orders table for each order based on the calculated sum.

Remember to adjust the column and table names according to your actual database schema. Adding a TotalPrice column in the Orders table is a common practice to improve query performance when you frequently need to retrieve the total price without recalculating it every time.