Java code to print keys and values from nested document in mongo

Question

For a mongo database which has the following details:

[{
    "Name" : "Krishna",
    "Fruits" : {
    "Apples" : 5,
    "Oranges" : 10
    }
},
{
    "Name" : "Kiran",
    "Fruits" : {
    "Plums" : 10,
    "Watermelons" : 1
    }
}]

I want to print the following output:

Krishna has 5 Apples, 10 Oranges

Kiran has 10 Plums, 1 Watermelons

Following is the snippet of code I wrote. Please help me in filling up the blanks. Please note that there is no limit on the kind of fruits that the user can have.

try {
    MongoDatabase database = mongoClient.getDatabase("test");
    MongoCollection < Document > collection = database.getCollection("inventory");
    MongoCursor < Document > cursor = collection.find().iterator();
    try {
        while (cursor.hasNext()) {
            Document doc = cursor.next();
            String name = doc.getString("Name"));
            //TODO: Fill inventory
            String inventory =

        System.out.println(name + " has " + inventory);
    }
} finally {
    cursor.close();
}
} catch (MongoException e) {
    e.printStackTrace();
}

Accept the solution proposed by Igor

What did you try so far? What is your specific question/problem? — Jan
– Jan, Commented Aug 11, 2015 at 12:16
I know how to query if i know the key. But in this case, i dont know what keys to expect and the keys are in a nested document: Fruits — Krishna
– Krishna, Commented Aug 11, 2015 at 12:20
possible duplicate of MongoDB extracting values from BasicDBObject (Java) — Neo-coder
– Neo-coder, Commented Aug 11, 2015 at 12:44
Probably my question is not understood properly. (1) I just want to access the inner document which is under "Fruits" (2) I want to iterate over all the keys in that document since i dont know what keys are present inside it — Krishna
– Krishna, Commented Aug 11, 2015 at 16:40

Igor · Accepted Answer · 2015-08-11 18:03:19Z

0

The easiest way that you can do:

    Map<String, Integer> map = (Map) document.get("Fruits");
    Iterator iterator = map.keySet().iterator();
    String inventory = " ";
    while(iterator.hasNext()) {
        String key = iterator.next().toString();
        int value = map.get(key);
        inventory += value + " " + key;
        if (iterator.hasNext()) {
            inventory += ", ";
        } else {
            inventory += ".";
        }
    }

This should be work but casting is not recommended thing, so better check this link and figure out how to avoid it with BsonReader:
http://mongodb.github.io/mongo-java-driver/3.0/bson/readers-and-writers/

answered Aug 11, 2015 at 18:03

Igor

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