Dealing with multiple error checks in NodeJS controller - node.js

Question

I need to validate multiple checks in my controller and throw possible errors to my route. Something like this:
Router:
send post var to controller
Controller:
throw error if post.categoria is blank
check in mysql if already exists
throw error if already exists
Router code:
// POST new
router.post('/', function(req, res, next){
// get post var
var post = {categoria: req.body.categoria};
// validate
controller.newCategoria(post).then(
result => {
// return valid result, I'll implement it later
res.json(result);
},
error => {
// return error to frontend
res.json(error);
}
);
});
Controller code:
module.exports.newCategoria = async (post) => {
// throw error if blank
if (post.categoria.length == 0)
throw "categoria is empty"; // portuguese
db.query('SELECT COUNT(id) AS count FROM categoria WHERE ?', post, function(err, result) {
if (err)
throw err;
if (JSON.stringify(result[0].count) >= 1)
throw new Error("already exists");
});
return "ok";
};
If I send and existing categoria I get: Rethrow non-MySQL errors
I tried to use a promise:
module.exports.newCategoria = async (post) => {
// check if blank
if (post.categoria.length == 0)
throw "blank categoria";
new Promise((resolve, reject) => {
db.query('SELECT COUNT(id) AS count FROM categoria WHERE ?', post, function(err, result) {
if (err)
return reject(err);
if (JSON.stringify(result[0].count) >= 1)
return reject(new Error("already exists"));
return resolve(result);
});
}).then(
resolve => {
// ok.. deal with it
console.log('ok');
console.log(resolve);
},
error => {
throw error;
}
).catch((error) => {
throw error;
});
return "ok";
};
I don't know how to throw it back to rote, I'm getting this error:
UnhandledPromiseRejectionWarning: Error: already exists
I'm new to NodeJS, I need a good practice for it. Thanks.

Answer 1

You need to return a Promise like so
module.exports.newCategoria = async (post) => {
return new Promise((resolve, reject) => {
// throw error if blank
if (post.categoria.length == 0)
reject(new Error("categoria is empty")); // make sure you are throwing Errors or else node will chastise you
db.query('SELECT COUNT(id) AS count FROM categoria WHERE ?', post, function(err, result) {
if (err)
reject(err);
else if (Number(result[0].count) >= 1) // compare ints to ints, not string to int
reject(new Error("already exists"));
else
resolve(result)
});
})
};
If you want to do more async stuff, here is one way you could refactor
const alreadyExists = x => x && x[0] && x[0].length > 1
const getCategoria = post => {
return new Promise((resolve, reject) => {
db.query(
'SELECT COUNT(id) AS count FROM categoria WHERE ?',
post,
(err, result) => {
if (err)
reject(err)
else if (alreadyExists(result))
reject(new Error('already exists'))
else
resolve(result)
},
)
})
}
module.exports.newCategoria = async post => {
const categoria = await getCategoria(post)
// insert here
}