Reusing QSqlQuery by using QSqlQuery::prepare()

PetrS82

Hello,
is possible to reuse an instance of QSqlQuery by redefinition of query by calling QSqlQuery::prepare(newSQL_string) after query.exec()?

If yes, is it neccessary to clear previous data by calling some function like QSqlQuery::clear() or QSqlQuery::finish() or ... before I will call prepare() function?

Or is neccessary to use for each SQL query the new instance of QSqlQuery?

Assume the code like this:

query.prepare("INSERT INTO PERSONS (Name, City) VALUES ('John', 'Boston')");
if (query.exec()) {
query.prepare("SELECT * FROM CARS WHERE CAR_ID = 10");
query.exec();
}

KroMignon

@PetrS82 Yes, no problem:

QSqlQuery query(dbConnection);

if(query.exec("INSERT INTO PERSONS (Name, City) VALUES ('John', 'Boston'))
{
     if(query.exec("SELECT * FROM CARS WHERE CAR_ID = 10"))
    {
        while(query.next())
        {
            // do stuff...
        }
    }
}

kshegunov

It's a good idea to call QSqlQuery::finish before you run your next prepare statement to tell the DB that it can release any locks or snapshots you may've acquired.

Kent-Dorfman

@PetrS82 said in Reusing QSqlQuery by using QSqlQuery::prepare():

query.prepare("INSERT INTO PERSONS (Name, City) VALUES ('John', 'Boston')");
if (query.exec()) {
query.prepare("SELECT * FROM CARS WHERE CAR_ID = 10");
query.exec();
}

Redefining the prepared statement query is a bad practice because it negates the objective of a prepared statement. Simply create another query object and keep your prepares linked to distinct query objects. If you are intent upon using a single query object then you might as well simply do immediate mode SQL in the exec("sql") fashion.

kshegunov

Unless you bind arguments, which arguably is much better than allowing for injection of invalid query data.