MySQL: Free the results when QSqlQuery::finished() is called

Calling mysql_stmt_free_result() frees the results of the last
executed query while keeping the prepared statement valid. This
allows to keep around prepared QSqlQueries without the overhead
of keeping all the results in memory.

Change-Id: I4589e90857cc4e9a6f9612799bfca967a67e2ab2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/plugins/sqldrivers/mysql/qsql_mysql.cpp b/src/plugins/sqldrivers/mysql/qsql_mysql.cpp
index f2ae3fbc47..80c0c9c522 100644
--- a/src/plugins/sqldrivers/mysql/qsql_mysql.cpp
+++ b/src/plugins/sqldrivers/mysql/qsql_mysql.cpp
@@ -197,6 +197,7 @@ protected:
     QSqlRecord record() const override;
     void virtual_hook(int id, void *data) override;
     bool nextResult() override;
+    void detachFromResultSet() override;
 
 #if MYSQL_VERSION_ID >= 40108
     bool prepare(const QString &stmt) override;
@@ -804,6 +805,15 @@ int QMYSQLResult::numRowsAffected()
     return d->rowsAffected;
 }
 
+void QMYSQLResult::detachFromResultSet()
+{
+    Q_D(QMYSQLResult);
+
+    if (d->preparedQuery) {
+        mysql_stmt_free_result(d->stmt);
+    }
+}
+
 QVariant QMYSQLResult::lastInsertId() const
 {
     Q_D(const QMYSQLResult);