Qt: QPSQL prepare doesn't work in class - qt

Question

I tried to outsource the code for the connection to a local PostgreSQL server from my "main.cpp" file into a seperate class called "database.cpp".
The connection worked just fine, when I had the code in the "main.cpp":
main.cpp
QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
QSqlQuery query(db);
qint32 declareConnection()
{
db.setHostName("127.0.0.1");
db.setPort(5432);
db.setDatabaseName("postgres");
db.setUserName("postgres");
db.setPassword("password");
return 0;
}
qint32 createUser(QString username, QString password)
{
if (db.open())
{
db.transaction();
query.prepare("INSERT INTO users (name, password) VALUES (?, ?);");
query.bindValue(0, username);
query.bindValue(1, toMD5(password));
query.exec();
query.finish();
db.commit();
db.close();
}
return 0;
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
qDebug() << "Declare Database: " << declareConnection();
qDebug() << "Create User: " << createUser("Testuser", "Testpassword");
return a.exec();
}
But after I put the functions in the "database.cpp", the prepare.query() fails every time I try to execute it.
Here's my current code:
main.cpp
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Database postgre;
qDebug() << "Declare Database: " << postgre.declareConnection();
qDebug() << "Create User: " << postgre.createUser("Testuser", "Testpassword");
return a.exec();
}
Database.h
class Database : public QObject
{
Q_OBJECT
public:
explicit Database(QObject *parent = 0);
qint32 declareConnection();
qint32 createUser(QString username, QString password);
QSqlDatabase db();
};
Database.cpp
QSqlDatabase Database::db()
{
return QSqlDatabase::database();
}
qint32 Database::declareConnection()
{
QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
db.setHostName("127.0.0.1");
db.setPort(5432);
db.setDatabaseName("postgres");
db.setUserName("postgres");
db.setPassword("password");
return 0;
}
qint32 Database::createUser(QString username, QString password)
{
if (db().open())
{
db().transaction();
QSqlQuery query(db());
query.prepare("INSERT INTO users (name, password) VALUES (?, ?);");
query.bindValue(0, username);
query.bindValue(1, toMD5(password));
query.exec();
query.finish();
db().commit();
db().close();
}
return 0;
}
The declaration of the database seems to work just fine, but when it comes to the "createUser()" function, there is always that problem with the "query.prepare()" command.
The database is open, so that works.
Also the transaction is in an open state, when I check in debug.
The prepare is false.
The query.exec() says: Syntaxerror at end of line LINE 1: EXECUTE ^.
QPSQL: Unable to create query.
WARNING: No open transaction. (But was open???)

Answer 1

The problem is here
void Database::declareConnection()
{
QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
you declared local variable db on a stack.
The decision is:
class Database : public QObject
{
...
QSqlDatabase & db() { return m_db; }
private:
QSqlDatabase m_db;
};
void Database::declareConnection()
{
m_db = QSqlDatabase::addDatabase("QPSQL");
...
}