Question

Here is my code-

DBClientBase *conn = NULL;
string err_msg;
ConnectionString cs = ConnectionString::parse(connString, err_msg);

if (!cs.isValid()) {
   throw "bad: " + err_msg;
}

try {
  conn = cs.connect(err_msg);
}
catch (DBException &e) {
   cout << "caught " << err_msg << endl;
   return 1;
}

if (!conn) {
   cout << "Unable to connect to DB" << endl;
   return 1;
}

I would expect MongoDB to throw exception in case DB is not reachable. However, I am finding that if (!conn) is getting satisfied.

Why

catch (DBException &e) {
   cout << "caught " << err_msg << endl;
   return 1;
}

block isn’t working?

Answer 1

From the current trunk source, ConnectionString::connect only seems to throw an exception when the string itself was invalid (and you already know that it was not, from your first conditional statement).

It just returns a NULL pointer and sets errMsg in all other cases.

In your defence, I couldn’t find this documented anywhere at all; a very basic example of connect was all I could locate.

string err_msg;
ConnectionString cs = ConnectionString::parse(connString, err_msg);

if (!cs.isValid()) {
   throw "bad: " + err_msg;
}

DBClientBase* conn = cs.connect(err_msg);

if (!conn) {
   cout << "Unable to connect to DB: " << err_msg << endl;
   return 1;
}