dataLayer.js

const { Client } = require('pg')
let { CommandsRunner, PsqlDriver } = require('node-db-migration');
let connectionString = `postgresql://${process.env.PG_USER}:${process.env.PG_PASSWORD}@${process.env.PG_HOST}:5432/${process.env.PG_DATABASE}`;

/**
 * Run database migrations from the ./migrations directory.
 */
exports.runMigrations = async () => {    
    const client = new Client({
        connectionString,
    });

    await client.connect();
    let migrations = new CommandsRunner({
        driver: new PsqlDriver(client),
        directoryWithScripts: __dirname + '/migrations',
    });
    await migrations.run('init');
    await migrations.run('migrate');
    await client.end();
}

/**
 * Return the version number stored in the database.
 */
exports.getDbVersion = async () => {
    const client = new Client({
        connectionString,
    });
    await client.connect();
    const queryResult = await client.query('SELECT version_number FROM version;');
    await client.end();

    return queryResult.rows[0].version_number;
}