QTcpSocket read data from DB and send to client

mrjj

Hi
That is very broad question.
Anyway, start with reading data using
https://doc.qt.io/qt-5/qsqlquery.html
Then when that works you can look into
QTCPSocket to send it.

Nio74

Am I on the right track?

qint64 ServerThings::sendToClient(QTcpSocket *socket, const QString &str)
{
    

    QByteArray arrBlock;
    QDataStream out(&arrBlock, QIODevice::WriteOnly);

   // QVector<QStringList> lst;
    QSqlQuery query;
        query.prepare("SELECT * FROM tabripa where  Nbusta =(?)");
        query.bindValue(0, str);
        
        query.exec();
  
    while (query.next()) {
        QSqlRecord record = query.record();
   
        for(int i=0; i < record.count(); i++)
        {
            out.device()->seek(0);
            out << quint16(arrBlock.size() - sizeof(quint16));
            
            out << record.value(i).toString();
        }
       
    }
    return socket->write(arrBlock);
    

    }

jsulm

@Nio74 said in QTcpSocket read data from DB and send to client:

out.device()->seek(0);

Why?!
You're overwriting previous record data in each iteration, so you will only send data from last record.

Nio74

would you say I should not be iterating? could you give me a practical example?

mrjj

@Nio74
Hi
the code "out.device()->seek(0); "
means go to start of "file" and in effect, it means
new data will overwrite what's already written to it.
Im not sure that is what you want ? I assume you want to put all record
into the arrBlock and send it to the other side ?

But Yes, it seems you are on the right track. 👍

jsulm

@Nio74 said in QTcpSocket read data from DB and send to client:

would you say I should not be iterating?

No, that's not what I said, just remove the line I pointed out...

VRonin

could you give me a practical example?

void ServerThings::sendToClient(QTcpSocket *socket, const QString &str)
{
Q_ASSERT(socket);
    QDataStream out(socket);
    QSqlQuery query;
        query.prepare("SELECT * FROM tabripa where  Nbusta =(?)");
        query.bindValue(0, str);
        if(!query.exec()) return;
    while (query.next()) {
        const QSqlRecord record = query.record();
        for(int i=0; i < record.count(); i++)
            out << record.value(i).toString();
    }
    }

Nio74

Good Day, I Try send string "70502" from client,the server should read data from database and retun at client. I did to debug but "arrBlock" seems empty.

this is my code:

void ServerThings::readClient()
{
    QTcpSocket *clientSocket = static_cast<QTcpSocket*>(sender());
    QDataStream in(clientSocket);
    //in.setVersion(QDataStream::Qt_5_10);
    for (;;)
    {
        if (!m_nNextBlockSize)
        {
            if (clientSocket->bytesAvailable() < sizeof(quint16)) { break; }
            in >> m_nNextBlockSize;
        }

        if (clientSocket->bytesAvailable() < m_nNextBlockSize) { break; }
        QString str;
        in >> str;

        emit gotNewMesssage(str);

        m_nNextBlockSize = 0;

        if (sendToClient(clientSocket, str) == -1)
        {
            qDebug() << "Some error occured";
        }
    }
}


qint64 ServerThings::sendToClient(QTcpSocket *socket, const QString &str)
{


    QByteArray arrBlock;
   Q_ASSERT(socket);
        QDataStream out(&arrBlock,QIODevice::WriteOnly);
        QSqlQuery query;
            query.prepare("SELECT * FROM tabripa where  Nbusta =(?)");
            query.bindValue(0, str);
            while (query.next()) {
            const QSqlRecord record = query.record();
            for(int i=0; i < record.count(); i++)
                out << record.value(i).toString();
        }
    return socket->write(arrBlock);


    }

See attacched the debug, sorry for my english

Nio74

I answer myself I forgot to run the query, now must to do the method for receiving

qint64 ServerThings::sendToClient(QTcpSocket *socket, const QString &str)
{


    QByteArray arrBlock;
   Q_ASSERT(socket);
        QDataStream out(&arrBlock,QIODevice::WriteOnly);
        QSqlQuery query;
            query.prepare("SELECT * FROM tabripa where  Nbusta =(?)");
            query.bindValue(0, str);
            query.exec();
            while (query.next()) {
            const QSqlRecord record = query.record();
            for(int i=0; i < record.count(); i++)
                out << record.value(i).toString();
        }
    return socket->write(arrBlock);


    }

Nio74

I tryed so:

but should I always use the QByteArray for send data at client?

SGaist

Hi,

Or you can assign stream to your socket and write to it.

Nio74

I did so and It's Work :))))

side Server:

qint64 ServerThings::sendToClient(QTcpSocket *socket, const QString &str)
{


         QByteArray byteArray;
        // QBuffer buffer(&byteArray);

        //buffer.open(QIODevice::WriteOnly);
        QDataStream stream(&byteArray,QIODevice::WriteOnly);
        QSqlQuery query;
        query.prepare("SELECT Nbusta,costo,vendita FROM tabripa where  Nbusta =(?)");
        query.bindValue(0, str);
        query.exec();
        while (query.next()){
            if(query.isValid()){
                code = query.record().value("Nbusta").toInt();
                pCost = query.record().value("costo").toDouble();
                pPublic = query.record().value("vendita").toDouble();

                stream << code <<pCost << pPublic ;

                //buffer.close();
            }

        }

        return socket->write(byteArray);


    }

side Client:

void ClientServices::readyRead()
{
   QDataStream in(tcpSocket);//QtcpSocket

    int code = 0;
    double pCost = 0;
    double pPublic = 0;

    in >> code >> pCost >> pPublic;

    qDebug() << code << pCost << pPublic;



}

I did not use the Qbuffer because on the client I am not able to integrate it, but if I use it on the server side and on the client no the data is received the same. How does it look? We accept suggestions!