Loading image from computer files save in database and display later

[JonB]

@GREYON said in Loading image from computer files save in database and display later:

collect it from computer files by opening file dialogand save it as QByteArray.

Use QFileDialog::getOpenFileName() to prompt the user to pick an existing file. Open it with QFile and use its methods to read its content as a QByteArray. Send that to your database to store as a BLOB.

[GREYON]

@JonB thanks for you help,however since am kind of stack,do you have any written example on how to do that?

[HoMa]

You stuff a QByteArray into the database, but you fetch a QString? This does not look good to me. I guess you should try to convert to a QByte Array here:

QString outimage =qry.value(0).toString();
QPixmap outpixmap=QPixmap(outimage);

[GREYON]

@HoMa thanks very much for your observation , however that was just the last option after fetching QByteArray like this

QByteArray outimage =qry.value(0).toByteArray();
QPixmap outpixmap=QPixmap();
outpixmap.loadFromData(outpixmap);
ui->label_6->setPixmap(outpixmap);
```  could not display anything on the label.At least when I used QString I was able to displayt the image though it's not the correct way of doing it.

[JonB]

@GREYON said in Loading image from computer files save in database and display later:

outpixmap.loadFromData(outpixmap);

That's an interesting line that you have copied from your source code.

[GREYON]

@JonB why have you said that its an interesting line?

[jsulm]

@GREYON said in Loading image from computer files save in database and display later:

why have you said that its an interesting line?

Take a closer look at that line please.
You're trying to load data into outpixmap from outpixmap - does that make sense? Shouldn't you load the pixmap from outimage?

[GREYON]

@jsulm okay let me look at it sir

[GREYON]

@GREYON You are right it supposed to be

outpixmap.loadDataFrom(outimage)

It was just an error when I was typing to post here but that's how it was in the actual cade.

[jsulm]

@GREYON What does outpixmap.loadFromData(outpixmap) return?

[J.Hilk]

how sure are you, that IMAGEDATA is actually of type BLOB ?

[JonB]

@GREYON said in Loading image from computer files save in database and display later:

It was just an error when I was typing to post here but that's how it was in the actual cade.

Please copy and paste source code, how else can people know what you actually have if you type it in? Wasted too much time over the years with people saying something is in their source when it turns out it is not....

[mrjj]

Hi
Did you look over this example?
https://wiki.qt.io/How_to_Store_and_Retrieve_Image_on_SQLite

[GREYON]

When i use this code :

  qry.lastError();
      while(qry.next())
        {
     QByteArray outimage =qry.value(0).toByteArray();
     QPixmap outpixmap=QPixmap();
    // outpixmap.loadFromData(outimage);
    int h=ui->label_6->height();
    int d=ui->label_6->width();
    outpixmap.loadFromData(outimage);
    outpixmap.scaled(d,h,Qt::IgnoreAspectRatio,Qt::SmoothTransformation);
    ui->label_6->setPixmap(outpixmap);
      }
     
    }

nothing is being displayed on the label ,am just getting the following error and i don't understand why .
![alt text](

[GREYON]

@mrjj thanks yes did look over it only that it was not very clear to me because it talk much using the screen short unlike when you loading it from the computer.I think its just because am still a learner in qt.

[JonB]

@GREYON
Start by checking the length of qry.value(0).toByteArray(), and indeed the length/number of bytes at the SQL side. Is this perhaps 0? loadFromData() returns a bool for a reason --- you need to check it.

[HoMa]

@GREYON
I was curiouse and typed in the code below. It worked w/o problems. So you are on the right track - maybe you go line to line and compare my code with yours.
btw: your

QPixmap out =QPixmap();

should be

QPixmap out;

and

QPixmap outpixmap=QPixmap(outimage)

should be

QPixmap outpixmap(outimage);

This is not the problem you have, just inefficient code.

To the experts here: I use the code below and only switch to a sqlite in memory database it no longer works. Any idea why this is?

void MainWindow::on_pushButton_clicked()
{
    QPixmap pixmap("../sqlPixmap/image.jpg");
    QByteArray ba;
    QBuffer bu(&ba);
    bu.open(QIODevice::WriteOnly);
    pixmap.save(&bu);

    QSqlDatabase db =QSqlDatabase::addDatabase ("QSQLITE");
    db.setDatabaseName ("../sqlPixmap/db.sqlite");
//    db.setDatabaseName (":memory:");
    db.open();

    QSqlQuery v("SELECT sqlite_version()");
    v.next();
    qDebug() << "sqlite version " << v.value (0);

    QSqlQuery q ("CREATE TABLE t (c)");

    q.prepare ("INSERT INTO t (c) VALUES (:pic)");
    q.bindValue (":pic", ba);
    if( ! q.exec()) {
        qDebug() << "could not store data";
    }

    /////////////////////////////////////////////

    q.prepare ("SELECT c FROM t");
    if( ! q.exec()) {
        qDebug() << "could in select query";
    }
    if( ! q.next()) {
        qDebug() << "failed to retrieve data";
    }
    QByteArray readBa =q.value (0).toByteArray ();

    QPixmap readPic;
    readPic.loadFromData(readBa);
    ui->lbl->setPixmap (readPic);
    ui->lbl->setScaledContents (true);
}

[SGaist]

Hi,

What exactly does not work ?

[HoMa]

Sorry for missing out on that.
All SQL calls have positive result, but the array is empty. Strange …

[Christian Ehrlicher]

@HoMa said in Loading image from computer files save in database and display later:

QPixmap pixmap("../sqlPixmap/image.jpg");
QByteArray ba;
QBuffer bu(&ba);
bu.open(QIODevice::WriteOnly);
pixmap.save(&bu);

Please check if the first line really works. Relaitve paths are not good since you don't know the current working directory of your program.