[Interest] Qt Sql BLOB data converting

[Yauheni Pervenenka]

Scott, thanks you for your time

On Mon, Nov 28, 2022 at 10:11 PM Scott Bloom <scott at towel42.com> wrote:

> @Christian Ehrlicher you beat me to the punch.
>
> If you dump out the value (not the size) you will see the QVariant is a of
> type QString not QByteArray
>
>         const auto value = query.value(0);
>         qDebug() << "value = " << value;
>         auto tmp = QVariant( value.toByteArray() );
>         qDebug() << "tmp = " << tmp;
>
> value =  QVariant(QString, "v10I-F½L\u009C{░?x\u009B)δ\u001EG#?????fóu??H")
> tmp =  QVariant(QByteArray,
> "v10I-F\xC2\xABL\xC2\x9C{\xC2\xB0\xEF\xBF\xBDx\xC2\x9B)\xC3\xAB\x1EG#\xDE\xA6\xEF\xBF\xBD\xEF\xBF\xBD\xEF\xBF\xBD\xEF\xBF\xBD""f\xC2\xA2u\xEF\xBF\xBD\xEF\xBF\xBD\xC4\xA6")
>
> This is the root cause of the problem.
>
> Ive hit this before, the query.value function should return a QByteArray
> type of QVariant, not a QString type when the column type is of type blob.
>
>     auto record = db.record( "test" );
>     qDebug() << "record =" << record;
>
> returns the correct record type
>
> record = QSqlRecord(1)
>  0: QSqlField("value", QByteArray, tableName: "test", required: yes,
> generated: yes, autoValue: false, readOnly: false) ""
>
> Whats interesting, is in my qsql_sqlite.cpp (the driver for the sql
> database,
>
> sqlite3_column_decltype16 returns "BLOB" but sqlite3_column_type returns
> SQLITE_TEXT
>
> in the init columns function, to determine which Qt type to use, it first
> gets the string name of the column, if empty then use  sqlite3_column_type
> otherwise it uses qGetColumnType
>
> So the Record is correct, but the return type is of QString not QByteArray
>
> Scott
>
>
>
>
> -----Original Message-----
> From: Interest <interest-bounces at qt-project.org> On Behalf Of Christian
> Ehrlicher
> Sent: Monday, November 28, 2022 10:41 AM
> To: Yauheni Pervenenka <yauheni.pervenenka at viber.com>;
> interest at qt-project.org
> Subject: Re: [Interest] Qt Sql BLOB data converting
>
>
> Am 28.11.2022 um 19:16 schrieb Yauheni Pervenenka via Interest:
> > Thiago, hello, thanks for your reply, sorry have no instructions for
> > create and insert, but have data base with one value which can't be
> > parsed correct(db is cut to one value for provide example)
> >
> > https://bugreports.qt.io/browse/QTBUG-108992
> >
> Your database looks strange to me - even though your column type according
> to the schema is BLOB:
>
> sqlite> .schema
> CREATE TABLE IF NOT EXISTS "test" (
>          "value" BLOB NOT NULL
> );
>
> the return value of sqlite3_column_type() is SQLITE_TEXT (3).
>
> Therefore the return value is treated as string and the data is screwed
> up. If I change the return value to SQLITE_BLOB (4) in the debugger, all is
> correct:
>
> qDebug() << value.toByteArray().toHex();
>
> -->
>
> "763130492d46ab4c9c7bb0e9789b29c3ab1e4723dea6c8e5d2f9b266a275e1fbe4a6"
>
>
>
> Christian
>
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