QtSql: execBatch() with SELECT statements

[herrmarder]

I am not an expert SQL user and I do not have much experience with the QtSql Module, I hope I am not missing something obvious:

I want to retrieve a list of blobs from my (sqlite) database with a batch command. But it does not work properly. isSelect() is not true for the query and I cannot get the results of the query.
Am I using the command correctly? Or should I simply do consecutive exec() commands. Will that have an effect on the speed?

Here is my sample code:

QString query_string = QString(
      "SELECT my_blob_column FROM my_table WHERE id = ? ;"
    );
  q.prepare(query_string);
  q.addBindValue(ids_in_qvariantlist);
 
  if (!q.execBatch()) {...}
 
  qDebug() << q.isSelect();  // is false
 
  while (q.next()) {  // is never true
    qDebug() << q.value(0).toByteArray()
  }

QString query_string = QString(
      "SELECT my_blob_column FROM my_table WHERE id = ? ;"
    );
  q.prepare(query_string);
  q.addBindValue(ids_in_qvariantlist);

  if (!q.execBatch()) {...}

  qDebug() << q.isSelect();  // is false

  while (q.next()) {  // is never true
    qDebug() << q.value(0).toByteArray()
  }

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edit:
I am running Qt 4.5.3 on OpenSuse 11.2

[JohannesMunk]

Why don't you build a list of the ids you want to retrieve. (I assume, that its not just all or some simple subset...)

QString idset = "(";
for (int i=0;i < list.length();++i)
{
  idset += QString::number(list.at(i));
  if (i <  list.length()-1)
   idset += ",";
}
idset += ")";
 
QSqlQuery q;
q.exec("SELECT my_blob_column FROM my_table WHERE id in "+idset+";");
while (q.next())
{
}
..

QString idset = "(";
for (int i=0;i < list.length();++i)
{
  idset += QString::number(list.at(i));
  if (i <  list.length()-1)
   idset += ",";
}
idset += ")";

QSqlQuery q;
q.exec("SELECT my_blob_column FROM my_table WHERE id in "+idset+";");
while (q.next())
{
}
..

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HIH

Johannes

[herrmarder]

Thank you Johannes,
I have tried using execBatch() so much that I did not see the obvious workaround :-)
Tobias