SQL/MySQL: retrieve default column value for QSqlDatabase::record()

Retrieve the default value (if set) of a column during
QSqlDatabase::record() but not for QSqlQuery::record() as it's done for
the other drivers which support retrieving the default column value.

Fixes: QTBUG-122723
Change-Id: I92e052bfa6d88e019c0151fbcbc1483a65770c55
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

src/plugins/sqldrivers/mysql/qsql_mysql.cpp

@@ -1475,12 +1475,39 @@ QSqlIndex QMYSQLDriver::primaryIndex(const QString &tablename) const
 
 QSqlRecord QMYSQLDriver::record(const QString &tablename) const
 {
+    Q_D(const QMYSQLDriver);
     if (!isOpen())
         return {};
     QSqlQuery i(createResult());
     QString stmt("SELECT * FROM %1 LIMIT 0"_L1);
     i.exec(stmt.arg(escapeIdentifier(tablename, QSqlDriver::TableName)));
-    return i.record();
+    auto r = i.record();
+    if (r.isEmpty())
+        return r;
+    // no binding of WHERE possible with MySQL
+    // escaping on WHERE clause does not work, so use mysql_real_escape_string()
+    stmt = "SELECT column_name, column_default FROM information_schema.columns WHERE table_name = '%1'"_L1;
+    const auto baTableName = tablename.toUtf8();
+    QVarLengthArray<char> tableNameQuoted(baTableName.size() * 2 + 1);
+#if defined(MARIADB_VERSION_ID)
+    const auto len = mysql_real_escape_string(d->mysql, tableNameQuoted.data(),
+                                              baTableName.data(), baTableName.size());
+#else
+    const auto len = mysql_real_escape_string_quote(d->mysql, tableNameQuoted.data(),
+                                                    baTableName.data(), baTableName.size(), '\'');
+#endif
+    if (i.exec(stmt.arg(QString::fromUtf8(tableNameQuoted.data(), len)))) {
+        while (i.next()) {
+            const auto colName = i.value(0).toString();
+            const auto recordIdx = r.indexOf(colName);
+            if (recordIdx >= 0) {
+                auto field = r.field(recordIdx);
+                field.setDefaultValue(i.value(1));
+                r.replace(recordIdx, field);
+            }
+        }
+    }
+    return r;
 }
 
 QVariant QMYSQLDriver::handle() const

src/sql/kernel/qsqlfield.cpp

@@ -208,6 +208,8 @@ void QSqlField::setPrecision(int precision)
     \since 6.8
 
     This property holds the default value for this field.
+    Only some database drivers supports this property. Currently
+    those are SQLite, PostgreSQL, Oracle and MySQL/MariaDB.
 */
 
 /*!

tests/auto/sql/kernel/qsqldriver/tst_qsqldriver.cpp

@@ -35,6 +35,7 @@ static bool driverSupportsDefaultValues(QSqlDriver::DbmsType dbType)
     case QSqlDriver::SQLite:
     case QSqlDriver::PostgreSQL:
     case QSqlDriver::Oracle:
+    case QSqlDriver::MySqlServer:
         return true;
     default:
         break;
@@ -132,8 +133,14 @@ void tst_QSqlDriver::record()
     for (int i = 0; i < fields.size(); ++i)
         QCOMPARE(rec.fieldName(i), fields[i]);
 
-    if (driverSupportsDefaultValues(dbType))
+    if (driverSupportsDefaultValues(dbType)) {
-        QCOMPARE(rec.field(QStringLiteral("name")).defaultValue().toString(), QStringLiteral("defaultVal"));
+        auto defVal = rec.field(QStringLiteral("name")).defaultValue().toString();
+        if (dbType == QSqlDriver::MySqlServer && defVal.startsWith('\'') && defVal.endsWith('\'')) {
+            qDebug() << "MariaDB 10.6 default string value is escaped:" << defVal;
+            defVal = defVal.mid(1, defVal.size() - 2);
+        }
+        QCOMPARE(defVal, QStringLiteral("defaultVal"));
+    }
 
     if (dbType == QSqlDriver::Oracle || dbType == QSqlDriver::DB2)
         tablename = tablename.toUpper();