Assertion: 13111:wrong type for field 3 != 4 - MongoDB C++ driver

Question

In my MongoDB database I have documents of this form:

   {    "timestamp" : "2012-01-15T17:56:14.85",
        "Event" : [
            {
                "id" : "1851236846",
                "qualifier_id" : "209"
            },
            {
                "id" : "378258775",
                "qualifier_id" : "57",
                "value" : "1"
            }
        ]
    }

   {   "timestamp" : "2012-01-15T16:06:09.378"

   }

Some of them contain the array Event some don't.

When I'm trying to process the data using the C++ MongoDB driver 2.4:

 while (cursor->more()) { 
  BSONObj bo = cursor->next();
  cout << "timestamp: " << bo.getStringField("timestamp") << std::endl;

  if(bo.hasElement("Event")) {
    cout<<"HERE"<< endl;

    std::vector<BSONElement> be = bo.getField("Event").Array(); // ---> at this line breaks!!

    for (unsigned int j = 0; j < be.size(); j++) {

              BSONObj bo2 = be[j].embeddedObject();
              cout << "Qualifier ID: " << bo2.getStringField("qualifier_id") << std::endl;
              cout << "Value: " << bo2.getStringField("value")<< std::endl;

    }
  }

I get this error:

  timestamp: 2012-01-15T16:06:06.529
   HERE
   Qualifier ID: 15
   Value: 

   Qualifier ID: 56
   Value: Back

  timestamp: 2012-01-15T16:06:07.560
   HERE
   Qualifier ID: 212
   Value: 14.6

   Qualifier ID: 141
   Value: 89.2

   Qualifier ID: 213
   Value: 5.9

   Qualifier ID: 56
   Value: Back

   Qualifier ID: 140
   Value: 46.7

  timestamp: 2012-01-15T16:06:09.378
  HERE
  Sun Jul 21 20:06:16.974 Assertion: 13111:wrong type for field (Event) 3 != 4
  caught wrong type for field (Event) 3 != 4

In conclusion the condition bo.hasElement("Event") is always true.(???) The program brakes here:

   std::vector<BSONElement> be = bo.getField("Event").Array();

When the array Event has no members.

Pease help!

Answer 1

I can help you with more info about the error: http://docs.mongodb.org/manual/reference/operator/type/#op._S_type 3 => Object 4 => Array