Question

I have the following document in my MongoDB test database:

> db.a.find().pretty()
{
    "_id" : ObjectId("5113d680732fb764c4464fdf"),
    "x" : [
            {
                "a" : 1,
                "b" : 2
            },
            {
                "a" : 3,
                "b" : 4
            }
          ]
}

I’m trying to access and process the elements in the “x” array. However, it seems that the Mongo driver is identifying it not as an array of JSON document, but as Date type, as shown in the following code:

auto_ptr<DBClientCursor> cursor = c.query("test.a", BSONObj());
while (cursor->more()) {      
  BSONObj r = cursor->next();
  cout << r.toString() << std::endl;
}

which output is:

{ _id: ObjectId('51138456732fb764c4464fde'), x: new Date(1360233558334) }

I’m trying to follow the documentation in http://api.mongodb.org/cplusplus and http://docs.mongodb.org/ecosystem/drivers/cpp-bson-array-examples/, but it is quite poor. I have found other examples of processing arrays, but always with simple types (e.g. array of integer), but not when the elements in the array are BSON documents themselves.

Do you have some code example of procesing arrays which elements are generic BSON elements, please?

Answer 1

At the end, it seems that embeddedObject() method was the key:

auto_ptr<DBClientCursor> cursor = c.query("test.a", BSONObj());
while (cursor->more()) { 
  BSONObj r = cursor->next();
  cout << "Processing JSON document: " << r.toString() << std::endl;
  std::vector<BSONElement> be = r.getField("x").Array();
  for (unsigned int i = 0; i<be.size(); i++) {
      cout << "Processing array element: " << be[i].toString() << std::endl;
      cout << "                 of type: " << be[i].type() << std::endl;
      BSONObj bo = be[i].embeddedObject();
      cout << "Processing a field: " << bo.getField("a").toString() << std::endl;
      cout << "Processing b field: " << bo.getField("b").toString() << std::endl;
  }
 }

I was wrongly retrieving a different ObjectID and a different type (Date instead of array) becuase I was looking to a different collection :$

Sorry for the noise. I hope that the fragment above helps others to figure out how to manipulate arrays using the MongoDB C++ driver.