Handle multiple request in Node.js

Question

How to handle multiple request at the same time? I couldn't find anything related to Nestjs and prisma. Does anybody has any recommended article or so?

To provide simple example - let's say I am building e-commerce API. I have simplified orderService in Nestjs. Business logic says, that user can not apply more than 1 voucher in an order. Let's say user somehow sends from UI two separate request at the same time. Condition order.vouchers.length > 1 is true for both requests which results accepting and updating both vouchers.

@Injectable('')
export class OrderService {
    constructor(private readonly database: DatabaseService) {}
    
    async applyVoucher(voucherDto: voucherDto) {
        const order = await this.database.orders.findOne({where: {id: voucherDto.orderId}})
        
        if (order.vouchers.length > 1) {
            return new HttpException('Can not add more than 2 voucher', 400);
        }
        
        await someHeavyWorkFunction()
        
        await this.database.orders.update({ where:{ id: voucherDto.orderId}, data: { vouchers: [...order.vouchers, voucherDto.voucher]}})
    
}

If I call my API endpoint which resolves calling this service three times in a row in a same time, expected behaviour is that 2 requests successfully pass and last request fails. However, this is not the case and all 3 requests pass ending up with 3 vouchers in database.

Answer 1

You can work with transactions, please follow this tutorial

A database transaction symbolizes a unit of work performed within a database management system (or similar system) against a database and treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes:

If you want to use an ORM like Typeorm for your projects, you can use this tutorial