FIX: Error when retrieving nonexisting entities.

src/lib/maoxdb.cpp

@@ -52,13 +52,14 @@ auto mxFromCaosDBMessages(const ce::Messages &messages) -> mxArray *;
  */
 auto transactionStatusToMessage(const caosdb::transaction::Transaction *const trans)
   -> std::pair<string, string> {
-  auto status = trans->GetStatus();
-  auto code = status.GetCode();
-  // Don't raise errors if it's only transaction errors (put into entity messages).
-  if (!status.IsError() || code == caosdb::StatusCode::GENERIC_TRANSACTION_ERROR) {
+  const auto &status = trans->GetStatus();
+  const auto &code = status.GetCode();
+  // Don't raise errors if it's only transaction errors (put into entity
+  // messages).
+  if (!status.IsError()) { // || code == caosdb::StatusCode::GENERIC_TRANSACTION_ERROR) {
     return std::pair<string, string>();
   }
-  string id = std::to_string(code);
+  string id = string("maoxdb:") + std::to_string(code);
   string text = status.GetDescription();
   return std::pair<string, string>(id, text);
 }

src/private/maox_retrieve.cpp

@@ -91,7 +91,7 @@ void mexFunction(int /*nlhs*/, mxArray *plhs[], int nrhs, const mxArray *prhs[])
     transaction->RetrieveById(id);
   }
   transaction->ExecuteAsynchronously();
-  auto t_stat = transaction->WaitForIt();
+  const auto &t_stat = transaction->WaitForIt();
   maoxdb::throwOctExceptionIfError(transaction.get());
   // Status must be OK or GENERIC_TRANSACTION_ERROR now.
   const auto &results = transaction->GetResultSet();