From 44ac742f730a5e8cac229067429eb2f5cb90105a Mon Sep 17 00:00:00 2001
From: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Date: Mon, 26 Sep 2022 19:58:27 +0200
Subject: QODBC: fix handling NULL values for strings

Qt6 added a slight behavior change in QVariant - an empty QString in a
QVariant no longer results in QVariant::isNull(). This created an issue
that qGetStringData() could no longer return a NULL value. On the other
side, NULL values in Qt5 could not be distinguished to an empty string
which we now can.

Fixes: QTBUG-106607
Pick-to: 6.2
Change-Id: Iddc6f7e8b97f5abc136bbbfd02d175b80152ac90
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
---
 src/plugins/sqldrivers/odbc/qsql_odbc.cpp | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

(limited to 'src/plugins/sqldrivers/odbc/qsql_odbc.cpp')

diff --git a/src/plugins/sqldrivers/odbc/qsql_odbc.cpp b/src/plugins/sqldrivers/odbc/qsql_odbc.cpp
index 49ceaf9c69..386ffccf36 100644
--- a/src/plugins/sqldrivers/odbc/qsql_odbc.cpp
+++ b/src/plugins/sqldrivers/odbc/qsql_odbc.cpp
@@ -370,7 +370,7 @@ static QMetaType qDecodeODBCType(SQLSMALLINT sqltype, bool isSigned = true)
     return QMetaType(type);
 }
 
-static QString qGetStringData(SQLHANDLE hStmt, int column, int colSize, bool unicode = false)
+static QVariant qGetStringData(SQLHANDLE hStmt, int column, int colSize, bool unicode)
 {
     QString fieldVal;
     SQLRETURN r = SQL_ERROR;
@@ -404,8 +404,7 @@ static QString qGetStringData(SQLHANDLE hStmt, int column, int colSize, bool uni
                             &lengthIndicator);
             if (r == SQL_SUCCESS || r == SQL_SUCCESS_WITH_INFO) {
                 if (lengthIndicator == SQL_NULL_DATA) {
-                    fieldVal.clear();
-                    break;
+                    return {};
                 }
                 // starting with ODBC Native Client 2012, SQL_NO_TOTAL is returned
                 // instead of the length (which sometimes was wrong in older versions)
@@ -431,8 +430,7 @@ static QString qGetStringData(SQLHANDLE hStmt, int column, int colSize, bool uni
                 break;
             } else {
                 qWarning() << "qGetStringData: Error while fetching data (" << qWarnODBCHandle(SQL_HANDLE_STMT, hStmt) << ')';
-                fieldVal.clear();
-                break;
+                return {};
             }
         }
     } else {
@@ -454,8 +452,7 @@ static QString qGetStringData(SQLHANDLE hStmt, int column, int colSize, bool uni
                             &lengthIndicator);
             if (r == SQL_SUCCESS || r == SQL_SUCCESS_WITH_INFO) {
                 if (lengthIndicator == SQL_NULL_DATA || lengthIndicator == SQL_NO_TOTAL) {
-                    fieldVal.clear();
-                    break;
+                  return {};
                 }
                 // if SQL_SUCCESS_WITH_INFO is returned, indicating that
                 // more data can be fetched, the length indicator does NOT
@@ -475,8 +472,7 @@ static QString qGetStringData(SQLHANDLE hStmt, int column, int colSize, bool uni
                 break;
             } else {
                 qWarning() << "qGetStringData: Error while fetching data (" << qWarnODBCHandle(SQL_HANDLE_STMT, hStmt) << ')';
-                fieldVal.clear();
-                break;
+                return {};
             }
         }
     }
@@ -620,7 +616,7 @@ static QSqlField qMakeFieldInfo(const SQLHANDLE hStmt, int i, QString *errorMess
 // by SQLColumns. The hStmt has to point to a valid position.
 static QSqlField qMakeFieldInfo(const SQLHANDLE hStmt, const QODBCDriverPrivate* p)
 {
-    QString fname = qGetStringData(hStmt, 3, -1, p->unicode);
+    QString fname = qGetStringData(hStmt, 3, -1, p->unicode).toString();
     int type = qGetIntData(hStmt, 4).toInt(); // column type
     QSqlField f(fname, qDecodeODBCType(type, p));
     QVariant var = qGetIntData(hStmt, 6);
@@ -1261,7 +1257,7 @@ QVariant QODBCResult::data(int field)
             }
             break;
         default:
-            d->fieldCache[i] = QVariant(qGetStringData(d->hStmt, i, info.length(), false));
+            d->fieldCache[i] = qGetStringData(d->hStmt, i, info.length(), false);
             break;
         }
         d->fieldCacheIdx = field + 1;
@@ -2392,8 +2388,7 @@ QStringList QODBCDriver::tables(QSql::TableType type) const
     }
 
     while (r == SQL_SUCCESS) {
-        QString fieldVal = qGetStringData(hStmt, 2, -1, d->unicode);
-        tl.append(fieldVal);
+        tl.append(qGetStringData(hStmt, 2, -1, d->unicode).toString());
 
         if (d->hasSQLFetchScroll)
             r = SQLFetchScroll(hStmt,
@@ -2490,11 +2485,11 @@ QSqlIndex QODBCDriver::primaryIndex(const QString& tablename) const
     // Store all fields in a StringList because some drivers can't detail fields in this FETCH loop
     while (r == SQL_SUCCESS) {
         if (usingSpecialColumns) {
-            cName = qGetStringData(hStmt, 1, -1, d->unicode); // column name
+            cName = qGetStringData(hStmt, 1, -1, d->unicode).toString(); // column name
             idxName = QString::number(fakeId++); // invent a fake index name
         } else {
-            cName = qGetStringData(hStmt, 3, -1, d->unicode); // column name
-            idxName = qGetStringData(hStmt, 5, -1, d->unicode); // pk index name
+            cName = qGetStringData(hStmt, 3, -1, d->unicode).toString(); // column name
+            idxName = qGetStringData(hStmt, 5, -1, d->unicode).toString(); // pk index name
         }
         index.append(rec.field(cName));
         index.setName(idxName);
-- 
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