Adapt SQL drivers to Qt 6 change of QVariant::isNull

In Qt 5, QVariant::isNull returned true if either the variant didn't
contain a value, or if the value was of a nullable type where the type's
isNull member function returned true.

In Qt 6, QVariant::isNull only returns true for variants that don't
contain a value; if the value contained is e.g. a null-QString or
QDateTime, then QVariant::isNull  returns false.

This change requires a follow up in the SQL drivers, which must
still treat null-values the same as null-variants, lest they write data
into the data base.

Add a static helper to QSqlResultPrivate that implements isNull-checking
of variants that contain a nullable type relevant for Sql, and add a
test case to the QSqlQuery test that exercises that code.

Pick-to: 6.2 6.3
Fixes: QTBUG-99408
Fixes: QTBUG-98471
Change-Id: I08b74a33aa3235c37d974f182da1f2bdcfd8217e
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/plugins/sqldrivers/oci/qsql_oci.cpp b/src/plugins/sqldrivers/oci/qsql_oci.cpp
index 5ba862f430..324e502f8c 100644
--- a/src/plugins/sqldrivers/oci/qsql_oci.cpp
+++ b/src/plugins/sqldrivers/oci/qsql_oci.cpp
@@ -515,7 +515,7 @@ int QOCIResultPrivate::bindValues(QVariantList &values, IndicatorArray &indicato
 
         OCIBind * hbnd = nullptr; // Oracle handles these automatically
         sb2 *indPtr = &indicators[i];
-        *indPtr = val.isNull() ? -1 : 0;
+        *indPtr = QSqlResultPrivate::isVariantNull(val) ? -1 : 0;
 
         bindValue(sql, &hbnd, err, i, val, indPtr, &tmpSizes[i], tmpStorage);
     }
@@ -1372,7 +1372,7 @@ bool QOCICols::execBatch(QOCIResultPrivate *d, QVariantList &boundValues, bool a
             // not a list - create a deep-copy of the single value
             QOCIBatchColumn &singleCol = columns[i];
             singleCol.indicators = new sb2[1];
-            *singleCol.indicators = boundValues.at(i).isNull() ? -1 : 0;
+            *singleCol.indicators = QSqlResultPrivate::isVariantNull(boundValues.at(i)) ? -1 : 0;
 
             r = d->bindValue(d->sql, &singleCol.bindh, d->err, i,
                              boundValues.at(i), singleCol.indicators, &tmpSizes[i], tmpStorage);
@@ -1469,7 +1469,7 @@ bool QOCICols::execBatch(QOCIResultPrivate *d, QVariantList &boundValues, bool a
         for (uint row = 0; row < col.recordCount; ++row) {
             const QVariant &val = boundValues.at(i).toList().at(row);
 
-            if (val.isNull() && !d->isOutValue(i)) {
+            if (QSqlResultPrivate::isVariantNull(val) && !d->isOutValue(i)) {
                 columns[i].indicators[row] = -1;
                 columns[i].lengths[row] = 0;
             } else {