How to use Typeorm to return ROW_NUMBER from a Postgres database

When using TypeORM to query a PostgreSQL database, we can achieve this using native SQL queries with the ROW_NUMBER() function. In this context, we typically employ a window function that assigns a unique sequence number to each row based on a specific ordering.

Assume you have a table named users, and you want to obtain the row number for each user based on the registration date. Below is how to implement this using TypeORM:

typescript
import { getManager } from "typeorm";

async function getUsersWithRowNumber() {
    const entityManager = getManager(); // or you can use getRepository or getConnection to obtain the entity manager
    const rawData = await entityManager.query(
        `SELECT 
            ROW_NUMBER() OVER (ORDER BY registration_date DESC) as row_num, 
            id, 
            name, 
            registration_date 
         FROM 
            users`
    );

    return rawData;
}

getUsersWithRowNumber().then(users => {
    console.log(users);
}).catch(error => {
    console.error('Error:', error);
});

In this example, we utilize the ROW_NUMBER() window function, specifying the ordering rules via the OVER clause (here, ordering by registration_date in descending order). ROW_NUMBER() assigns a unique sequential integer to each row, starting from 1.

Note:

• When using native SQL queries, ensure proper validation and sanitization of inputs to prevent SQL injection attacks.
• In production environments, consider database performance and query optimization.

This approach allows you to fully leverage the capabilities of the PostgreSQL database while implementing complex queries within TypeORM.