How to Store and Retrieve Image on SQLite

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Images (or any other binary data, from files or otherwise) can be stored in a database. One way to do it is converting the data into a QByteArray, and insert it into the database as a Binary Large OBject (BLOB).

Below is a full example of such a workflow, including reading the image back from the database and displaying it:

#include <QtSql>
#include <QtWidgets>

int main( int argc, char *argv[] )
{
    QApplication app( argc, argv );

    // Set up database
    QString dbName( "myDatabase.db3" );
    QFile::remove( dbName ); // delete sqlite file if it exists from a previous run
    QSqlDatabase db = QSqlDatabase::addDatabase( "QSQLITE" );
    db.setDatabaseName( dbName );
    db.open();
    QSqlQuery query = QSqlQuery( db );
    query.exec( "CREATE TABLE IF NOT EXISTS imgTable ( filename TEXT, imagedata BLOB )" );

    // Generate an image (in this case a screenshot) and store it in a QByteArray
    QScreen *screen = app.primaryScreen();
    QPixmap inPixmap = screen->grabWindow( 0 );
    QByteArray inByteArray;
    QBuffer inBuffer( &inByteArray );
    inBuffer.open( QIODevice::WriteOnly );
    inPixmap.save( &inBuffer, "PNG" ); // write inPixmap into inByteArray in PNG format

    // Alternatively, load an image file directly into a QByteArray
    // QFile file("screenshot.png");
    // if (!file.open(QIODevice::ReadOnly)) return;
    // QByteArray inByteArray = file.readAll();

    // Insert image bytes into the database
    // Note: make sure to wrap the :placeholder in parenthesis
    query.prepare( "INSERT INTO imgTable (filename, imagedata) VALUES ('screenshot.png', :imageData)" );
    query.bindValue( ":imageData", inByteArray );
    if( !query.exec() )
        qDebug() << "Error inserting image into table:\n" << query.lastError();

    // Get image data back from database
    if( !query.exec( "SELECT imagedata from imgTable" ))
        qDebug() << "Error getting image from table:\n" << query.lastError();
    query.first();
    QByteArray outByteArray = query.value( 0 ).toByteArray();
    QPixmap outPixmap = QPixmap();
    outPixmap.loadFromData( outByteArray );
    db.close();

    // Display image
    QLabel myLabel;
    myLabel.setPixmap( outPixmap );
    myLabel.show();

    return app.exec();
}