Return NEWID() from a SQL Query

Lany

I'm not a expert in SQL, I started to work in this project (and SQL) at the start of this week.
Here's the full code.

QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
db.setConnectOptions();
db.setDatabaseName("Driver={SQL Server};Server=" + m_str_adresseBaseSQL
                   + ";Database=" + m_str_nomBaseQSL + ";Uid=" + m_str_nomUtilisateur 
                   + ";Pwd=" + m_str_passUtilisateur + ";");

if (db.open()){
    QSqlQuery query;
    query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
	       "SET @myid = NEWID();"
	       "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
	       "SELECT @myid;");
    qDebug() << query.next();
    qDebug() << query.value(0).toString();
    db.close();
}

And the debug output:

false
QSqlQuery::value: not positioned on a valid record
""

JonB

@Lany
https://doc.qt.io/qt-5/qsqlquery.html#exec-1 also returns a bool value. Check that. When you discover it's returning false, debug out https://doc.qt.io/qt-5/qsqlquery.html#lastError.

Lany

Here's the result of

qDebug() << query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
                       "SET @myid = NEWID();"
                       "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
                       "SELECT @myid;");
qDebug() << query.next();
qDebug() << query.value(0).toString();
qDebug() << query.lastError().text();

Debug output:

true
false
QSqlQuery::value: not positioned on a valid record
""
" "

JonB

@Lany
If QSqlQuery::next() is returning false I would see what query.lastError() on the immediately following line returns (I don't know whether that gets set, try it). I would read https://doc.qt.io/qt-5/qsqlquery.html#next, where restrictions are mentioned, e.g. for all I know/I suspect that for your statement https://doc.qt.io/qt-5/qsqlquery.html#isSelect is returning false.

Christian Ehrlicher

I'm unsure if the qt mysql driver can handle multiple queries - I would guess no.

Lany

I tried this

qDebug() << query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
                       "SET @myid = NEWID();"
                       "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
                       "SELECT @myid;");
qDebug() << query.lastError().text();
qDebug() << query.isActive();
qDebug() << query.isSelect();
qDebug() << query.next();
qDebug() << query.value(0).toString();

the result:

true
" "
true
false
false
QSqlQuery::value: not positioned on a valid record
""

The query is not in a SELECT state, as mentioned by Christian, I think this driver can't handle multiple query.
I'm going to look for another solution.

Thanks!

KroMignon

@Lany said in Return NEWID() from a SQL Query:

I'm going to look for another solution.

Perhaps you can try to send the SQL statement through QSqlDatabase::exec() ?

Mucip

Hi,
I think you want to insert a record and get the record serila number from DB.
I guess it depends of what you use as database but in my case I use PostgreSQL and in this situation you have good SQL command like below:

//Yeni kaydet yapılıyor...
    QSqlQuery kayitDb(baglanti::mdb());
    kayitDb.prepare("INSERT INTO teklif(teklif_no, teklif_tarih, teklif_tip, aciklama, cari_kod, teslim_sure, odeme_tip, odeme_vade, teklif_kur, proje_kod) "
                    "VALUES(:teklif_no, :teklif_tarih, :teklif_tip, :aciklama, :cari_kod, :teslim_sure, :odeme_tip, :odeme_vade, :teklif_kur, :proje_kod) RETURNING sira_no;");

    kayitDb.bindValue(":teklif_no", ui->lETeklifNo->text());
    kayitDb.bindValue(":teklif_tarih", ui->dateTeklifTarih->date());
    kayitDb.bindValue(":teklif_tip", ui->lETeklifTip->text() );
    kayitDb.bindValue(":aciklama", ui->plainAciklama->toPlainText());
    kayitDb.bindValue(":cari_kod", ui->lECariKod->text().toInt());
    kayitDb.bindValue(":teslim_sure", ui->lETeslim->text());

    kayitDb.bindValue(":odeme_tip", ui->cBOdeme->currentText() );
    kayitDb.bindValue(":odeme_vade", ui->lEVade->text() );
    kayitDb.bindValue(":teklif_kur", ui->comboKur->currentText() );



     //Sending and returning serial ID...
    if(kayitDb.exec() && kayitDb.first())
    {
        int belgeSiraNo = kayitDb.value(0).toInt();
         ui->lESiraNo->setText(kayitDb.value(0).toString());


            if(detayKaydet(belgeSiraNo))
            {
                //İşlem sonu
                QMessageBox::information(this, "Tamamdır :)", "Fiş: " + ui->lESiraNo->text() + " sıra numarası ile kaydedildi.");
                ekranTemizle();
                iptalKonum();
            }

    } else
    {
        QMessageBox::critical(this, "Hata", "Veritabanına ulaşılamadı!\n"+kayitDb.lastError().text() );
        return;
    }

You're sending INSERT sql and reading returning serila value.

Regards,
Mucip:

kshegunov

Just use the api, here you go: https://doc.qt.io/qt-5/qsqlquery.html#lastInsertId
There's little sense in trying to emulate something that's not standard and is already implemented in the driver.

Lany

@kshegunov
The ID is generated by the db not by "me"

query.exec("INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (NEWID(), '0');");
qDebug() << query.lastInsertId().toString();

result:

"0"

In the db I have something like this :

315FD979-F300-4493-A0B9-4B5FE64A8F45

kshegunov

@Lany said in Return NEWID() from a SQL Query:

The ID is generated by the db not by "me"

Yes, that's why the client library and the driver on top of it knows about it and can give it back to you. It's not necessary to do a query to emulate the behavior.

PS. You need to handle the variant you got properly, not just blindly convert it to a string.

qDebug() << query.lastInsertId().type();

should help. Also, please make sure that TEST_ID is a primary key in the database (i.e. is properly indexed).

Lany

@kshegunov
The returned type is :

QVariant::double

TEST_ID is a primary key (PK, uniqueidentifier, not null)
If I try this

qDebug() << query.lastInsertId().toDouble();

The returned value is :

kshegunov

What database engine is this? MySQL, PgSQL, MSSQL?

Lany

Microsoft SQL server 2014

kshegunov

Right, sorry I was misled about the talk about MySql. Anyways, you really should auto-generate the id, not insert it manually (probably not the problem here, just saying). I haven't worked with MS for ages. Check if the driver supports lastInstertId at all.

qDebug() << db.driver()->hasFeature(QSqlDriver::LastInsertId);

If it doesn't then you're stuck to using non-standard queries. That means once you run the insert, you run a second query to fetch the inserted id.