Loading image from computer files save in database and display later

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.

GREYON

@JonB thanks people for your help,after going through documentation and one of example which I was given a here ,I found out that the code below is one having a problem,it was storing a file in a data base as a file path and not as Byte.


QByteArray HOME::bigimage;
void HOME::on_commandLinkButton_clicked()
{
 // QByteArray bigimage;
 QString filename=QFileDialog::getOpenFileName(this,tr("Open image"),"/",tr("Image Files(*.png;*.jpg;*.bmp)"));
 bigimage +=filename;

 QPixmap pixmap=QPixmap(filename);
 ui->label_8->setText(filename);
}```

So I had to change to something like this and it worked.

QByteArray HOME::bigimage;
void HOME::on_commandLinkButton_clicked()
{
// QByteArray bigimage;
QString filename=QFileDialog::getOpenFileName(this,tr("Open image"),"/",tr("Image Files(.png;.jpg;*.bmp)"));

Qfile file(filename)
if(!file.open(QIODevice::ReadOnly) return;
bigimage=file.readAll();

HoMa

@Christian-Ehrlicher It really does. I change only the file name from what is here to ":memory:" (like in the line below, which is commented out) and the picture can no longer be retreived.

Here the code with all calls tested:

    try
    {
        QPixmap pixmap("../sqlPixmap/image.jpg");
        QByteArray ba;
        QBuffer bu(&ba);
        bu.open(QIODevice::WriteOnly);
        pixmap.save(&bu);
        if( pixmap.width ()<= 0 || pixmap.height () <= 0) throw "Loading image from file failed";

        QSqlDatabase db =QSqlDatabase::addDatabase ("QSQLITE");
        db.setDatabaseName ("../sqlPixmap/db.sqlite");
        //db.setDatabaseName (":memory:");
        if( ! db.open()) throw "database could not be opened";

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

        QSqlQuery q ("CREATE TABLE t (c)"); // executes on creation

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

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

        q.prepare ("SELECT c FROM t");
        if( ! q.exec()) throw "failed in select query";

        if( ! q.next()) throw "failed to move to data set";

        QByteArray readBa =q.value (0).toByteArray ();
        if( 0 >= readBa.size ()) throw "returned data is empty";

        QPixmap readPic;
        readPic.loadFromData(readBa);
        ui->lbl->setPixmap (readPic);
        ui->lbl->setScaledContents (true);
    }
    catch(const char* error)
    {
        qDebug() << error;
        return;
    }

JonB

@GREYON
Not sure what happened to your QPixmap pixmap=QPixmap(filename); line now. After reading a QPixmap from a file (or elsewhere) you can/should always check bool QPixmap::isNull() const. That would cover e.g. "file not found" as well as "error reading contents of file as pixmap".

GREYON

This is the correct one

QByteArray HOME::bigimage;
void HOME::on_commandLinkButton_clicked()
{
// QByteArray bigimage;
QString filename=QFileDialog::getOpenFileName(this,tr("Open image"),"/",tr("Image Files(.png;.jpg;*.bmp)"));

Qfile file(filename)
if(!file.open(QIODevice::ReadOnly) return;
bigimage=file.readAll();

JonB

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

QPixmap pixmap("../sqlPixmap/image.jpg");
db.setDatabaseName ("../sqlPixmap/db.sqlite");

As @Christian-Ehrlicher commented, you simply should not use a relative path here, as you just do not know where that will be. See my https://forum.qt.io/topic/138832/export-qtableview-to-pdf-with-a-push-button/8 to another user on the same matter.

HoMa

@JonB Thx for your efforts - I appreciate that. But this is a test program for the single purpose of playing around with sqlite, blobs (and meanwhile "in memory"). Anyone who wants to use the code will have to modify the path to the picture - no matter if it is absolute or relative. For this reason I think it makes no difference in this specific case.

GREYON

@HoMa thanks for that code I will try it as well

HoMa

Couldn't resist and created a version, which works also with an in memory database.
@GREYON : Pls check out https://github.com/Schachigel/Qt-QPixmap-2-SQLite.git

have fun!

GREYON

@HoMa okay thanks let me check bro