Iterating multiple documents using cursor in Mongo

Question

I am facing an issue while iterating documents in mongo database using Java code. I am iterating records on the basis of User_ID value as "demo" in the collection. While iteration its storing the most recent record instead of all matching data. The code is as below:

public BasicDBObject Demo1(String User_ID) throws Exception {
        DB db = ConnectToDB.getConnection();
        DBCollection collection = db.getCollection("demo");
        BasicDBObject document = new BasicDBObject();
        BasicDBObject Project_Detail = new BasicDBObject();
        document.put("User_ID", User_ID);
        field.put("ProjectName", 1);
        field.put("ProjectNumber", 1);
        field.put("_id", 0);
        DBCursor cursor = collection.find(document, field);
while (cursor.hasNext()) {
                    BasicDBObject object=new BasicDBObject();
                    object = (BasicDBObject) cursor.next();

                    Project_Detail.append("ProjectName", object.get("ProjectName"));
                    Project_Detail.append("ProjectNumber", object.get("ProjectNumber"));
                    System.out.println("Project_Detail value is:" + Project_Detail);

                }
return Project_Detail;
}

My mongo collection is as below, which is having two documents:

{
    "_id" : ObjectId("59dc85905f0446bfb39417f5"),
    "User_ID" : "demo",
    "ProjectNumber" : "1",
    "ProjectName" : "Project1",
 },
{
    "_id" : ObjectId("59dc85a15f0446bfb39417f9"),
    "User_ID" : "demo",
    "ProjectNumber" : "2",
    "ProjectName" : "Project2",
 }

When I run the above code, it shows the following result for given User_ID: "demo":

 {
    "ProjectName": "Project2",
    "ProjectNumber": "2"}

But the desired result should be :

{
    "ProjectName": "Project1",
    "ProjectNumber": "1"},
{
    "ProjectName": "Project2",
    "ProjectNumber": "2"}

It seems like it is updating the record in second counter and hence so updating the value in the second document in the second iteration. Please specify If I can fetch both the matching records and store these in the result. Thanks for any help.

Answer 1

In second iteration you are replacing values of same key. That's why only one value remains in result. You should use BasicDBList to store multiple BasicDBObject :

Eg

BasicDBList Project_Detail = new BasicDBList();
while (cursor.hasNext()) {
                    BasicDBObject object=new BasicDBObject();
                    object = (BasicDBObject) cursor.next();
                    BasicDBObject temp = new BasicDBObject();
                    temp.append("ProjectName", object.get("ProjectName"));
                    temp.append("ProjectNumber", object.get("ProjectNumber"));
                    Project_Detail.add(temp);

                }

Convert BasicDBList to BasicDBObject :

    BasicDBObject result = new BasicDBObject();
    result.putAll(Project_Detail.toMap());