CODEWITHSUNDEEP
c++sqlqtsqliteqsqlquery
Efog
Efog

Reputation: 1179

QSqlQuery size() always returns -1

QSqlQuery query;
QString queryText("SELECT * FROM section");
query.exec(queryText);
qDebug() << query.size(); //always -1
while (query.next()) qDebug() << query.value(0).toString(); //got 16 records

Method size() always returns -1.

Upvotes: 10

Views: 5707

Answers (4)

Nejat
Nejat

Reputation: 32635

query.size() is not supported with SQLite. But you can get the number of rows with a workaround.

QSqlQuery::last () retrieves the last record in the result, if available, and positions the query on the retrieved record. After calling last() you can retrieve the index of the last record and position the query before the first record using first() and previous():

int numberOfRows = 0;
if(qry.last())
{
    numberOfRows =  qry.at() + 1;
    qry.first();
    qry.previous(); 
}

Upvotes: 15

Jablonski
Jablonski

Reputation: 18504

From QSqlQuery::size:

Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if the database does not support reporting information about query sizes. Note that for non-SELECT statements (isSelect() returns false), size() will return -1. If the query is not active (isActive() returns false), -1 is returned.

To determine the number of rows affected by a non-SELECT statement, use numRowsAffected().

Your query isSelect and active, but SQLite is one of the databases for which the size of the query is not directly available.

To prove this, call this for example:

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

It returns false.

Upvotes: 6

papadave
papadave

Reputation: 21

I get the same problem when using qsqlite in qt5. query.size always return -1, so i use query.first() instead.

QString username = ui->usernameInput->text();
QString password = ui->passwordInput->text();
QString command = "SELECT * FROM user WHERE username = '" + username + "' AND password = '" + password + "'";
QSqlQuery query;
if (query.exec(command)) {
    qDebug() << query.size(); // the size will always -1 when using QSqlite
    if (query.first()) { // so i use query.first() to check if there has any result
        QMessageBox::information(this, "Login success.", "You have successfully logged in!");
    } else {
        QMessageBox::information(this, "Login failed.", "Please Check the username and password");
    }
}

Upvotes: 2

Ivan Romanov
Ivan Romanov

Reputation: 1228

For myself I use this function

int sqlSize(QSqlQuery query)
{
    int initialPos = query.at();
    // Very strange but for no records .at() returns -2
    int pos = 0;
    if (query.last())
        pos = query.at() + 1;
    else
        pos = 0;
    // Important to restore initial pos
    query.seek(initialPos);
    return pos;
}

Upvotes: 3

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