QTcpSocket read data from DB and send to client

Nio74

hello, you have some examples I have to read from a database and on the client table I have to read Name, surname and insert it in an Array and let the client read it

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!