How to get, use, and close a DB connection using callbacks

db-config.js

module.exports = {
  user: 'hr',
  password: 'oracle',
  connectString: 'localhost:1521/orcl',
  poolMax: 20,
  poolMin: 20,
  poolIncrement: 0
};

employees.js

const oracledb = require('oracledb');

function getEmployee(empId, getEmployeeCallback) {
  oracledb.getConnection(function(err, conn) {
    if (err) {
      console.log('Error getting connection', err);
      getEmployeeCallback(err);
      return;
    }

    console.log('Connected to database');

    conn.execute(
      `select *
      from employees
      where employee_id = :emp_id`,
      [empId],
      {
        outFormat: oracledb.OBJECT
      },
      function(err, result) {
        if (err) {
          console.log('Error executing query', err);

          getEmployeeCallback(err);

          conn.close(function(err) {
            if (err) {
              console.log('Error closing connection', err);
            } else {
              console.log('Connection closed');
            }
          });

          return;
        }

        console.log('Query executed');

        getEmployeeCallback(null, result.rows[0]);

        conn.close(function(err) {
          if (err) {
            console.log('Error closing connection', err);
          } else {
            console.log('Connection closed');
          }
        });
      }
    );
  });
}

module.exports.getEmployee = getEmployee;

index.js

const oracledb = require('oracledb');
const dbConfig = require('./db-config.js');
const employees = require('./employees.js');

oracledb.createPool(dbConfig, function(err) {
  if (err) {
    console.log(err);
    return;
  }

  employees.getEmployee(101, function(err, emp) {
    if (err) {
      console.log(err);
      return;
    }

    console.log(emp);
  });
});

package.json

{
  "name": "callbacks",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "Dan McGhan <dan.mcghan@oracle.com> (https://jsao.io/)",
  "license": "ISC",
  "dependencies": {
    "oracledb": "^1.13.1"
  }
}

This gist is a demo app that shows how to get, use, and close a DB connection using callbacks. See the related blog post and the main post for the series for more details.