How to escape binary data for insertion into PostgreSQL database with Qt?

Question

I'm trying to insert binary data (QImage) into a PostgreSQL 8.4.9 bytea column from Qt 4.8. My code looks like this:

QImage image;
QByteArray ba;
QBuffer buffer(&ba);
image.save(&buffer, "PNG"); // Save the QImage data into the QBuffer

QSqlQuery query = QSqlQuery(database);
query.prepare("INSERT INTO images (image) "
              "VALUES (:image)");

query.bindValue(":image", ba);
query.exec();
qDebug() << query.lastError().text();

This works, but I get the following error:

WARNING: nonstandard use of \ in a string literal LINE 1: ...XECUTE
qpsqlpstmt_1 ('\211PNG... HINT: Use the escape string syntax for
backslashes, e.g., E'\'

How can I escape the data properly to avoid this warning?

EDIT :

Here is some essential information regarding this topic: http://www.postgresql.org/docs/8.4/static/datatype-binary.html

The way I see it, each byte should be surrounded by E''::bytea before passing to bindValue. How can I accomplish this?

I'm not sure what are you trying to do by supplying a binary data where a column name should go (the first mention of :image in your INSERT statement). — Milen A. Radev
– Milen A. Radev, Commented Feb 15, 2012 at 13:13
That was just a typo. I cleaned columns not related to this problem from the code to make the question more general. — Marek Miettinen
– Marek Miettinen, Commented Feb 15, 2012 at 18:07

Milen A. Radev · Accepted Answer · 2012-02-16 08:41:00Z

3

Have a look at the docs for .bindValue - you most probably need to indicate that the value is binary:

query.bindValue(":image", ba, QSql::In | QSql::Binary);

edited Feb 16, 2012 at 8:41

answered Feb 15, 2012 at 18:34

Milen A. Radev

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1 Comment

Marek Miettinen Over a year ago

This doesn't have any effect. And I believe it should be QSql::In | QSql::Binary

Community · Accepted Answer · 2017-05-23 11:52:36Z

0

Have you tried to use the E'' around your QByteArray? I don't know if that will work for an image but it seems to work for strings.

String literals and escape characters in postgresql

edited May 23, 2017 at 11:52

CommunityBot

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answered Feb 15, 2012 at 13:39

masebase

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