best way to load image from db

[C167]

Hi, i'm currently loading images from a sqlite3 blob-field using this code:

void ImageViewer::loadImage ( int pic )
{
	QSqlQuery query ( QSqlDatabase::database() );
	query.prepare ( "SELECT data FROM img_images WHERE id = :id" );
	query.bindValue ( ":id", img_list[pic] );
	query.exec();
	if ( query.next() )
	{
		return QImage::fromData ( query.value ( 0 ).toByteArray() ) );
	}
	else
	{
		return QImage();
	}
}

void ImageViewer::loadImage ( int pic )
{
	QSqlQuery query ( QSqlDatabase::database() );
	query.prepare ( "SELECT data FROM img_images WHERE id = :id" );
	query.bindValue ( ":id", img_list[pic] );
	query.exec();
	if ( query.next() )
	{
		return QImage::fromData ( query.value ( 0 ).toByteArray() ) );
	}
	else
	{
		return QImage();
	}
}

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Now i found some examples in one of my Qt-Books:

QImage ImageCollection::getImage( int id )
{
	QSqlQuery qrx;
	qry.prepare ( "SELECT data FROM images WHERE id = :id" );
	qry.bindValue ( ":id", id );
	if ( !qry.exec() ) qFatal ( "Failed to get image" );
	if ( !qry.next() ) qFatal ( "Failed to get image id" );
	QByteArray array = qry.value ( 0 ).toByteArray();
	QBuffer buffer ( &array );
	buffer.open ( QIODevice::ReadOnly );
	QImageReader reader ( &buffer, "PNG" );
	QImage image = reader.read();
	return image;
}

QImage ImageCollection::getImage( int id )
{
	QSqlQuery qrx;
	qry.prepare ( "SELECT data FROM images WHERE id = :id" );
	qry.bindValue ( ":id", id );
	if ( !qry.exec() ) qFatal ( "Failed to get image" );
	if ( !qry.next() ) qFatal ( "Failed to get image id" );
	QByteArray array = qry.value ( 0 ).toByteArray();
	QBuffer buffer ( &array );
	buffer.open ( QIODevice::ReadOnly );
	QImageReader reader ( &buffer, "PNG" );
	QImage image = reader.read();
	return image;
}

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Which code is better, if i know that i only have one image format in the database and why? which one is the fastest?
Using Qt4.4b1, 4.4rc1 is compiling atm. System is Debian Sid.
C167

[jacek]

IMO the first version is better, because it's shorter and supports all possible images formats. It might be a bit slower, because Qt must detect the format, but I don't think you will notice the difference.

[Lykurg]

Hi,

because of QImage::fromData is defined as

QImage QImage::fromData(const uchar *data, int size, const char *format)
{
    QByteArray a = QByteArray::fromRawData(reinterpret_cast<const char *>(data), size);
    QBuffer b;
    b.setData(a);
    b.open(QIODevice::ReadOnly);
    return QImageReader(&b, format).read();
}

QImage QImage::fromData(const uchar *data, int size, const char *format)
{
    QByteArray a = QByteArray::fromRawData(reinterpret_cast<const char *>(data), size);
    QBuffer b;
    b.setData(a);
    b.open(QIODevice::ReadOnly);
    return QImageReader(&b, format).read();
}

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both are equal. But as jacek mentioned your code is shorter in "front end", so I would prefer it.

If you need speed improvement store all images in the database in the same image format, and specify it in fromRawData(). Also if img_list is an private member and you definitely know the content you may use

query.exec( "SELECT data FROM img_images WHERE id = " +  QString::number(img_list[pic]));

query.exec( "SELECT data FROM img_images WHERE id = " +  QString::number(img_list[pic]));

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(assuming img_list[pic] will return an integer)

Lykurg