mongodb - Sub document id value

Question

I have a collection.

look
 { "_id" : 13.0 , "tenantref" : { "$id" : 3.0}}

I need to retrieve the value of id 3.0 using java. I am getting null pointer exception.

    BasicDBObject field = new BasicDBObject();
    BasicDBObject field = new BasicDBObject();
    field.put("tenantref.$id", 1);

    DBCursor cursor = mongo.getDB("number").getCollection("testthree").find(query,field);   

    while (cursor.hasNext()) 
    {       
    System.out.println(cursor.next().get("tenantref.$id"));
    }

I am getting null pointer exception. How do I need to get the value?

on what line does the null pointer exception occur? – Philipp Sep 05 '12 at 13:09 — Philipp, Sep 05 '12 at 13:09

score 1 · Accepted Answer · answered Sep 05 '12 at 13:13

1

cursor.next().get("tenantref.$id"));

The get() function of BasicDBObject does not support the dot syntax. You have to traverse the object hierarchy by hand. Try

((DBObject)cursor.next().get("tenantref")).get("$id");

answered Sep 05 '12 at 13:13

Philipp

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mongodb - Sub document id value

1 Answers1