Nodejs loops iterating before executing the mysql queries embedded inside them - mysql

Question

I am unable to return the projectIds array after the mysql statements have finished executing as the loop is iterating before executing them. This results in empty array being returned everytime.
function fetchProjects (projects, userId, callback) {
projectIds = [];
Object.keys(projects).forEach(function(key) {
var row = projects[key];
const sql = 'create table if not exists users_' + row.project_id + '(sno int primary key auto_increment, iteration_no int not null, user_id int not null, foreign key(iteration_no) references pro_' + row.project_id + '(iteration_no), foreign key(user_id) references user(user_id))';
connection.query(sql, function(err, result) {
if(err) {
console.log(err.sqlMessage);
return callback(err.sqlMessage, false);
} else {
// console.log("First statement executed");
const sql1 = "select distinct t1.project_id, t1.project_name, t1.client, t1.initial_department_id, t1.start_date, t1.status, t1.current_department, t1.currently_assigned_user from project t1, users_" + row.project_id + " t2 where t1.project_id = '" + row.project_id + "' and (select user_id from users_" + row.project_id +" where user_id = " + userId + ")";
connection.query(sql1, function(err, result1) {
if(err) {
console.log(err.sqlMessage);
return callback(err.sqlMessage, false);
} else {
if(result1.length > 0) {
console.log(result1);
projectIds.push(result1);
}
}
});
}
});
// console.log("Iterating");
});
return callback(false, projectIds);
}

Answer 1

You are trying to execute callback style code in forEach which doesn't wait for the query to finish. That is the reason you are getting emoty array. I would make few modifications
Use promise version of the query method. Check the documentation of mysql node package
Use for..of loop instead of forEach.
Make the function async
Also await when you call the promise version of query method.
Hope this helps.