express + mysql : clean code for complex queries - mysql

Question

I am using express with mysql for my api.
This code works fine :
exports.addAuthor = function(req, res, next) { // POST /authors {{{
let sqlquery = '';
let a = checkAuthor(req.body);
if(!a.valid) {
var myerr = new Error(a.msg);
myerr.status = 400;
return next(myerr);
}
//
myPool.getConnection(function(err, connection) {
if (err) { return next(err); }
// check if exists first
sqlquery = 'SELECT COUNT(*) AS nb FROM authors';
sqlquery += ' WHERE name = "' + a.name + '" AND firstname = "' + a.firstname + '";';
connection.query(sqlquery, function(err, rows) {
if (err) {
connection.release();
return next(err);
} else {
if (rows[0].nb > 0) {
connection.release();
let myerr = new Error('This author already exists !');
myerr.status = 400;
return next(myerr);
} else {
sqlquery = 'INSERT INTO authors (name, firstname)';
sqlquery += ' VALUES ("' + a.name + '","' + a.firstname + '")';
connection.query(sqlquery, function(err, rows) {
connection.release();
if (err) { return next(err); }
if (rows.affectedRows) {
res.json({name: a.name, firstname: a.firstname, id: rows.insertId});
}
});
}
}
});
});
}; // }}}
First, I would like to reuse the code to get the id of the author, if it exists, so define one function for that.
Secondly I would like to write simpler and cleaner code as I imagine more complex code with several requests to the DB for future cases. (12 lines only to check if author exists !)
I know it has to deal with asynchronous nature of the Mysql queries.
I read many things but I am still no able to write proper code to acheive that.
Thanks to point me to right way to manage not so simple case.
JPM
I think I succeeded to make work some code that was not working yesterday !
I do not know yet if it is the best way however.
I took some piece of code somewhere but I do not remember where (probably here).
Here it is :
const execQuery = (sql, params) => new Promise((resolve, reject) => { // {{{
myPool.getConnection(function(err, connection) {
if (err) {
reject(err);
} else {
connection.query(sql, function(err, rows) {
connection.release();
if (err) {
reject(err);
} else {
resolve(rows);
}
})
}
});
}); // }}}
async function getIDAuthor(a) { // {{{
sqlquery = 'SELECT id FROM authors';
sqlquery += ' WHERE name = "' + a.name + '" AND firstname = "' + a.firstname + '"';
if(a.id) { // case update name of known author
sqlquery += ' AND id <> ' + a.id;
}
try {
rows = await execQuery(sqlquery);
if(rows.length>0) {
return rows[0].id;
} else {
return 0;
}
} catch (error) {
return -1;
}
} // }}}
exports.addAuthor = async function(req, res, next) { // POST /authors {{{
let sqlquery = '';
let a = checkAuthor(req.body); // {{{
if(!a.valid) {
var myerr = new Error(a.msg);
myerr.status = 400;
return next(myerr);
} // }}}
let ide = await getIDAuthor(a);
if(ide>0) {
let myerr = new Error('This author already exists !');
myerr.status = 400;
return next(myerr);
}
sqlquery = 'INSERT INTO authors (name, firstname)';
sqlquery += ' VALUES ("' + a.name + '","' + a.firstname + '")';
try {
rows = await execQuery(sqlquery);
if (rows.affectedRows) {
res.json({name: a.name, firstname: a.firstname, id: rows.insertId});
}
} catch (error) {
return next(error);
}
}; // }}}
I have not yet checked all possible errors.
Feel free to advise me or correct me if needed.

Answer 1

I took code and ideas from https://nemethgergely.com/error-handling-express-async-await/
So it looks now like this:
exports.addAuthor = asyncMiddleware(async function(req, res, next) { // POST /authors {{{
let sqlquery = '';
let rows;
//
let a = checkAuthor(req.body);
if(!a.valid) { throw boom.badRequest(a.msg); }
let ide = await getIDAuthor(a);
if(ide>0) { throw boom.badRequest('Cet auteur existe déjà !'); }
//
sqlquery = 'INSERT INTO authors (name, firstname)';
sqlquery += ' VALUES ("' + a.name + '","' + a.firstname + '")';
rows = await execQuery(sqlquery);
if (rows.affectedRows) {
res.json({name: a.name, firstname: a.firstname, id: rows.insertId});
}
}); // }}}
In fact this does not handle all error cases. Forget it. Still at start point. Grrrrrr.