multiple nested callback functions before parent's callback in javascript - mysql

Question

Im using expressjs and mysql package.
I have a user table, each user could have many skills, projects, certifications stored in different tables. How can I get all of these data into a single user object.
getUserDataById(req.params.id, function (user) {
if (user) {
res.send(user);
}
}
var getUserDataById = function (id, callback) {
connection.query(userSql, id, function (err, rows) {
if (rows[0]) {
user = new User(rows[0]); //parse row data to user obj
// The main problem
//get skills and projects.... and asign to user obj
parseArrayData(skillSql, user.id, Skill, function (skills) {
user.skills = skills;
}
);
parseArrayData(projectSql, user.id, Project, function (project) {
user.projects = projects;
}
);
// is here
callback(user);
}
});
}
var parseArrayData = function (query, id, Obj, callback) {
connection.pool.query(query, id, function (err, rows) {
if (err) {
throw err;
} else {
console.log('rows',rows);
var array = [];
for (var i = 0; i < rows.length; i++) {
array[i] = new Obj(rows[i]); // map obj's attributes with fields
};
callback(rows);
}
});
};

Answer 1

You might have these different tables with names (assume): users, skills, projects, certifications;
function to get result from db for query;
function executeQuery(tablename, userId, callback) {
var sql = 'select * from ' + tablename + ' where id = ' + userId;
connection.query(sql, function (err, rows) {
if (err) { callback(err, null); }
else { callback(null, rows); }
})
}
Function that will fetch all results for user id and return json object;
var getUserDataById = function (userId, callback) {
executeQuery('users', userId, function(users) {
executeQuery('projects', userId, function(projects) {
executeQuery('skills', userId, function(skills) {
executeQuery('certifications', userId, function(certifications) {
var result = { // format you result.
id: userId,
users: users,
projects: projects,
skills: skills,
certifications: certifications
};
callback(result);
});
});
});
});
callback(null);
});
Usage:
getUserDataById(req.params.id, function (user) {
if (user) {
res.send(user);
}
}