how to save QVector<float> into sqlite as BLOB?

[lni]

Hi,

I am trying to save QVector<float> into database as a BLOB field, but I am not getting the data back correctly. Here is the code.

Can anyone please tell me what is the problem?

Many thanks!

QByteArray toByarray( const QVector<float>& data )
{
  QByteArray result;
  QDataStream bWrite( &result, QIODevice::WriteOnly );
  bWrite << data;
 
  return result;
 
}
 
QVector<float> toVectorF( const QByteArray& buffer )
{
  QVector<float> result;
  QDataStream bRead( buffer );
  bRead >> result;
 
  return result;
 
} 
 
int saveToDB( const QVector<float>& vec )
{
  QSqlQuery query( db );
 
  query.prepare( "insert into MyTable ( array ) values ( ? )" );
  query.bindValue( 0, toByarray( vec ) );
 
  int id( -1 );
  if ( query.exec() ) {
    id = query.lastInsertId().toInt();
  }
 
  return id;
}
 
QVector<float> readFromDB( int id )
{
  QSqlQuery query( db );
 
  query.prepare( "select array from MyTable where id=?" );
  query.bindValue( 0, id );
 
  QVector<float> result;
  if ( query.exec() && query.next() ) {
    result = toVectorF( query.value( 0 ).toByteArray() );
  }
 
  return result;
}

QByteArray toByarray( const QVector<float>& data )
{
  QByteArray result;
  QDataStream bWrite( &result, QIODevice::WriteOnly );
  bWrite << data;

  return result;

}

QVector<float> toVectorF( const QByteArray& buffer )
{
  QVector<float> result;
  QDataStream bRead( buffer );
  bRead >> result;

  return result;

} 

int saveToDB( const QVector<float>& vec )
{
  QSqlQuery query( db );

  query.prepare( "insert into MyTable ( array ) values ( ? )" );
  query.bindValue( 0, toByarray( vec ) );

  int id( -1 );
  if ( query.exec() ) {
    id = query.lastInsertId().toInt();
  }

  return id;
}

QVector<float> readFromDB( int id )
{
  QSqlQuery query( db );

  query.prepare( "select array from MyTable where id=?" );
  query.bindValue( 0, id );

  QVector<float> result;
  if ( query.exec() && query.next() ) {
    result = toVectorF( query.value( 0 ).toByteArray() );
  }

  return result;
}

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[ChrisW67]

What is not correct about what you get back?
Do you have a valid id to retrieve? Does your insert succeed? Does your insert return a valid id? Does the id overflow an int?

[lni]

It creates a record in the table as I can see using sqlitebrowser and returns a valid id.

I use that id to read back the BLOB data, and convert back to QVector<float>, the vector length is correct, but the content is wrong.

The QVector I save is
QVector(0, 41.41, 69.29, 98.1, 126.92, 155.77, 184.64, 213.48, 242.15, 271.06)

But when I read back and convert back to QVector, I get:
QVector(0, 0.59, 0.75, 1.09, 1.5, 1.7, 1.83, 2.13, 2.15, 1.89)

[lni]

Problem solved.

It is stupid that the sql statement missing a commas.