Initialize the QSqlQuery to be invalid when creating a sql model

When QSqlQueryModel or QSqlTableModel is created it will create a
QSqlQuery which defaults to using the default QSqlDatabase connection.

If this connection belongs to another thread then it will throw a
warning as this is not safe to use. Since the QSqlQuery is always
recreated when a query is set, the instance which is a member of
the class can effectively be invalid until a new one is set.

Task-number: QTBUG-69213
Change-Id: I68a5dd59fe62788f531d59a0680da11b118ee383
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/sql/models/qsqlquerymodel_p.h

@@ -75,7 +75,7 @@ public:
     void initColOffsets(int size);
     int columnInQuery(int modelColumn) const;
 
-    mutable QSqlQuery query;
+    mutable QSqlQuery query = { QSqlQuery(0) };
     mutable QSqlError error;
     QModelIndex bottom;
     QSqlRecord rec;

src/sql/models/qsqltablemodel_p.h

@@ -93,7 +93,7 @@ public:
     QSqlTableModel::EditStrategy strategy;
     bool busyInsertingRows;
 
-    QSqlQuery editQuery;
+    QSqlQuery editQuery = { QSqlQuery(0) };
     QSqlIndex primaryIndex;
     QString tableName;
     QString filter;

tests/auto/sql/models/qsqltablemodel/tst_qsqltablemodel.cpp

@@ -31,11 +31,29 @@
 #include "../../kernel/qsqldatabase/tst_databases.h"
 #include <QtSql>
 #include <QtSql/private/qsqltablemodel_p.h>
+#include <QThread>
 
 const QString test(qTableName("test", __FILE__, QSqlDatabase())),
                    test2(qTableName("test2", __FILE__, QSqlDatabase())),
                    test3(qTableName("test3", __FILE__, QSqlDatabase()));
 
+// In order to catch when the warning message occurs, indicating that the database belongs to another
+// thread, we have to install our own message handler. To ensure that the test reporting still happens
+// as before, we call the originating one.
+//
+// For now, this is only called inside the modelInAnotherThread() test
+QtMessageHandler oldHandler = nullptr;
+
+void sqlTableModelMessageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg)
+{
+    if (type == QtWarningMsg &&
+        msg == "QSqlDatabasePrivate::database: requested database does not "
+               "belong to the calling thread.") {
+        QFAIL("Requested database does not belong to the calling thread.");
+    }
+    if (oldHandler)
+        oldHandler(type, context, msg);
+}
 
 class tst_QSqlTableModel : public QObject
 {
@@ -116,6 +134,7 @@ private slots:
 
     void sqlite_bigTable_data() { generic_data("QSQLITE"); }
     void sqlite_bigTable();
+    void modelInAnotherThread();
 
     // bug specific tests
     void insertRecordBeforeSelect_data() { generic_data(); }
@@ -276,6 +295,10 @@ void tst_QSqlTableModel::init()
 void tst_QSqlTableModel::cleanup()
 {
     recreateTestTables();
+    if (oldHandler) {
+        qInstallMessageHandler(oldHandler);
+        oldHandler = nullptr;
+    }
 }
 
 void tst_QSqlTableModel::select()
@@ -2100,5 +2123,29 @@ void tst_QSqlTableModel::invalidFilterAndHeaderData()
     QVERIFY(!v.isValid());
 }
 
+class SqlThread : public QThread
+{
+public:
+    SqlThread() : QThread() {}
+    void run()
+    {
+        QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE", "non-default-connection");
+        QSqlTableModel stm(nullptr, db);
+        isDone = true;
+    }
+    bool isDone = false;
+};
+
+void tst_QSqlTableModel::modelInAnotherThread()
+{
+    oldHandler = qInstallMessageHandler(sqlTableModelMessageHandler);
+    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
+    CHECK_DATABASE(db);
+    SqlThread t;
+    t.start();
+    QTRY_VERIFY(t.isDone);
+    QVERIFY(t.isFinished());
+}
+
 QTEST_MAIN(tst_QSqlTableModel)
 #include "tst_qsqltablemodel.moc"