perform async multiple Mysql queries on Node - mysql

Question

I'm using node with Mysql and here's my problem.
I'm trying to add new photos on my database and return it as an array
here is my function :
function addNewPhotos(_id, files) {
var deferred = Q.defer();
var new_photos = []
_.each(files, function (one) {
var data = [
one.path,
_id,
0
]
var sql = 'INSERT INTO photos(photo_link, id_user, isProfil) VALUES (?, ?, ?)';
db.connection.query(sql, data, function (err, result) {
if (err)
deferred.reject(err.name + ': ' + err.message);
var sql = 'SELECT id_user, photo_link, isProfil FROM `photos` WHERE id = ?';
if (result){
db.connection.query(sql, [result.insertId], function(err, photo) {
if (err) deferred.reject(err.name + ': ' + err.message);
if (photo) {
new_photos.push(photo[0]);
}
});
}
})
})
deferred.resolve(Array.prototype.slice.call(new_photos));
return deferred.promise}
The Insert works well but i can't retrieve the results to send them back to the client. (my array is empty)
Thanks.

Answer 1

Always promisify at the lowest level, in this case db.connection.query().
if(!db.connection.queryAsync) {
db.connection.queryAsync = function(sql, data) {
return Q.Promise(function(resolve, reject) { // or possibly Q.promise (with lower case p), depending on version
db.connection.query(sql, data, function(err, result) {
if(err) {
reject(err);
} else {
resolve(result);
}
});
});
};
}
Now the higher level code becomes very simple :
function addNewPhotos(_id, files) {
var sql_1 = 'INSERT INTO photos(photo_link, id_user, isProfil) VALUES (?, ?, ?)',
sql_2 = 'SELECT id_user, photo_link, isProfil FROM `photos` WHERE id = ?';
return Q.all(files.map(function(one) {
return db.connection.queryAsync(sql_1, [one.path, _id, 0]).then(function(result) {
return db.connection.queryAsync(sql_2, [result.insertId]);
});
}));
};
To prevent a single failure scuppering the whole thing, you might choose to catch individual errors and inject some kind of default ;
function addNewPhotos(_id, files) {
var sql_1 = 'INSERT INTO photos(photo_link, id_user, isProfil) VALUES (?, ?, ?)',
sql_2 = 'SELECT id_user, photo_link, isProfil FROM `photos` WHERE id = ?',
defaultPhoto = /* whatever you want as a default string/object in case of error */;
return Q.all(files.map(function(one) {
return db.connection.queryAsync(sql_1, [one.path, _id, 0]).then(function(result) {
return db.connection.queryAsync(sql_2, [result.insertId]);
}).catch(function() {
return defaultPhoto;
});
}));
};

Answer 2

Do the return in your async loop function when all has been done
function addNewPhotos(_id, files) {
var deferred = Q.defer();
var new_photos = [];
var todo = files.length;
var done = 0;
_.each(files, function (one) {
var data = [
one.path,
_id,
0
]
var sql = 'INSERT INTO photos(photo_link, id_user, isProfil) VALUES (?, ?, ?)';
db.connection.query(sql, data, function (err, result) {
if (err)
deferred.reject(err.name + ': ' + err.message);
var sql = 'SELECT id_user, photo_link, isProfil FROM `photos` WHERE id = ?';
if (result){
db.connection.query(sql, [result.insertId], function(err, photo) {
if (err) deferred.reject(err.name + ': ' + err.message);
if (photo) {
new_photos.push(photo[0]);
}
if(++done >= todo){
deferred.resolve(Array.prototype.slice.call(new_photos));
return deferred.promise
}
});
}
else
{
if(++done >= todo){
deferred.resolve(Array.prototype.slice.call(new_photos));
return deferred.promise;
}
}
})
})
}