SQLite+Qt: Select from table always returns single row

Question

I use the following piece of code to fetch data from SQLite DB using Qt:

QSqlQuery wordQuery( QString( "SELECT id, word FROM Words WHERE ref_id = :ref_id" ) );
wordQuery.bindValue( ":ref_id", refId );
wordQuery.setForwardOnly( true );
wordQuery.exec( );

while( wordQuery.next( ) ) {
    // obtain data from `wordQuery` using QSqlQuery::value( )
}

The Words table do contain rows with ref_id field equal to needed value. I've checked this with sqlbrowser supplied as Qt demo application. But QSqlQuery::next( ) returns true only the first time and I cannot fetch rest of rows.

BTW, here I found similar question but for me backward iteration doesn't work

Below I put the whole function code:

QList<Word> LyricsMasterModel::fetchWords( const DbId &refId )
{
QList<Word> result;

if ( !db.isOpen( ) && !db.open( ) ) {
    return result;
}

QSqlQuery wordQuery;
wordQuery.setForwardOnly( true );
wordQuery.prepare( QString( "SELECT id, word FROM %1 WHERE ref_id = :ref_id" )
    .arg( WORDS_TABLE_NAME ) );
wordQuery.bindValue( ":ref_id", refId );
if ( !wordQuery.exec( ) ) {
    qDebug( ) << "SQL QUERY ERROR:" << wordQuery.lastError( ).text( );
}

const QSqlRecord wordTuple = wordQuery.record( );
const int idIndex = wordTuple.indexOf( "id" );
Q_ASSERT( -1 != idIndex );
const int wordIndex = wordTuple.indexOf( "word" );
Q_ASSERT( -1 != wordIndex );

while (wordQuery.next()) {
    Word word;

    word.setId( wordQuery.value( idIndex ).toByteArray( ) );
    word.setSongId( refId );
    word.setWord( wordQuery.value( wordIndex ).toString( ) );

    result << word;
}

db.close( );
return result;
}

Solution: I didn't manage to find the reason of the problem, but the following variant appeared to be the working one:

QSqlQuery wordQuery;
wordQuery.prepare( QString( "SELECT id, word FROM %1 WHERE ref_id = :ref_id" )
    .arg( WORDS_TABLE_NAME ) );
wordQuery.bindValue( ":ref_id", refId );
const bool res = wordQuery.exec( );
Q_ASSERT( res );

if ( wordQuery.last( ) ) {
    do {
        // do stuff
    } while (wordQuery.previous());
}

Answer 1

Your code has one major issue for the binding, namely:

QSqlQuery::QSqlQuery(const QString & query = QString(), QSqlDatabase db = QSqlDatabase())

Constructs a QSqlQuery object using the SQL query and the database db. If db is not specified, or is invalid, the application's default database is used. If query is not an empty string, it will be executed.

So, your query will be executed during the construction since it is not empty, and the bind is already too late for that.

I would personally construct the instance with an empty string as the default, and then do an explicit preparation as per documentation.

So, I would write something like this:

QSqlQuery wordQuery();
wordQuery.setForwardOnly(true);
wordQuery.prepare("SELECT id, word FROM Words WHERE ref_id = :ref_id");
wordQuery.bindValue(":ref_id", refId);
if (!wordQuery.exec())
    qDebug() << "SQL QUERY ERROR:" << wordQuery.lastError().text();

while (wordQuery.next()) {
    // obtain data from `wordQuery` using QSqlQuery::value( )
}