Is this a safe implementation of a generic SQL execute function? - c++

Question

Suppose the following implementation of a generic function to query a database using MySQL:
bool execute(const sql::SQLString query, std::vector<sql::ResultSet*> &results)
{
// ConnectionPool holds premade connections to the database
sql::Connection* conn = ConnectionPool::getInstance()::getConnection();
std::unique_ptr<sql::Statement> stmt;
bool success = false;
try
{
stmt.reset( conn->createStatement() );
stmt->execute( query );
do
{
results.push_back( stmt->getResultSet() );
} while ( stmt->getMoreResults() )
success = true;
}
catch ( ... )
{
// Other catch() statements are not a part of this question
std::cerr << "Exception caught!" << std::endl;
success = false;
}
conn->commit();
ConnectionPool::getInstance()::returnConnection( conn );
return success;
}
According to this example for retrieving results from a query, the ResultSet needs to be explicitly deleted. In regard to the implementation above, does this mean the vector of ResultSet pointers is safe to use (i.e., the objects they point to are not deleted by the deletion of the creating Statement)?
Also, am I doing anything unspeakably evil with this implementation?

Answer 1

The following implementation is safer. This is because the ResultSet is tied to the Connection, rather than the Statement. If the connection is closed, destroyed, or used for another purpose prior to the results being read, the ResultSet objects may become defunct and cause an abort condition. It is safer to let the calling function handle the Connection on its own.
Note that a better implementation would be for the sql::Connection* parameter to be std::unique_ptr< sql::Connection >&, but my personal needs dictate this cannot be done at this time.
bool execute(sql::Connection *conn, const sql::SQLString query, std::vector< std::unique_ptr<sql::ResultSet> > &results)
{
std::unique_ptr<sql::Statement> stmt;
bool success = false;
try
{
stmt.reset( conn->createStatement() );
stmt->execute( query );
do
{
results.emplace_back( stmt->getResultSet() );
} while ( stmt->getMoreResults() )
success = true;
}
catch ( ... )
{
// Other catch() statements are not a part of this question
std::cerr << "Exception caught!" << std::endl;
success = false;
}
conn->commit();
return success;
}