Mongodb Java 3.4 - get fields from embedded document

Question

I can't retrieve the address fields from my embedded document. I haven't seen any solutions for the 3.4 MongoDB driver.

System.out.println("Selecting Person ");

MongoCollection<Document> collection = mdb.getCollection("Person");
MongoCursor<Document> cursor = collection.find().iterator();

try {           
    while (cursor.hasNext()) {
        Document temp_person_doc=cursor.next();
        Document temp_address_doc=temp_person_doc.get("address");   
        String houseNo=temp_address_doc.getString("houseNo");       
    }
} finally {
    cursor.close();
}

Here is the document structure.

{
    "_id" : "5aae9920982f271ba4b08735",
    "firstName" : "homer",
    "surname" : "simpson",
    "address" : {
        "houseNo" : 742,
        "address" : "evergreen terrace",
        "city" : "springfield",
    }
}

glytching · Accepted Answer · 2018-03-19 17:03:14Z

I can see two issues with your code:

This will not return a document

Document temp_address_doc=temp_person_doc.get("address");

The houseNo attribute is an Integer not a String

String houseNo=temp_address_doc.getString("houseNo");

If you just change get("address") to get("address", Document.class) then you'll be on the right track.

For example:

Document temp_person_doc = cursor.next();

// get the sub document _as a_ Document
Document temp_address_doc = temp_person_doc.get("address", Document.class);

// get the houseNo attribute (which is an integer) from the sub document
Integer houseNo = temp_address_doc.getInteger("houseNo");
// get the address attribute (which is a string) from the sub document
String address = temp_address_doc.getString("address");

// prints 742
System.out.println(houseNo);    
// prints evergreen terrace
System.out.println(address);

Key points to note:

You must read the sub document as a Document
You must read the houseNo attribute as an Integer

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