How to delete the key/value pair when the Value is of type "Null" (on update)

Question

I'm practicing with the database mongoDB inside a Java project.

I have a Collection "Object" wich holds all documents with information about "objects". These "objects" are represented bij a Class in Java called "LoanboardObject". An Object can be made/changed with an web application that sends the data with a Post message to the Server. The Object is created and the parameters are stored in the object.

LoanBoardObject

public class LoanboardObject implements ILoanBoardEntity {

    private ObjectId id;
    private String objectName;
    private String objectCode;
    private String category;
    private Boolean lent = false;
    private String description = "";
    private Boolean enabled = false;

    public BasicDBObject toDBObject() {
        BasicDBObject object = new BasicDBObject();
        object.put("_id", id);
        object.put("object_name", objectName);
        object.put("object_code", objectCode);
        object.put("category", category);
        object.put("lent", lent);
        object.put("description", description);
        object.put("enabled", enabled);
        return object;
    }

    ...
}

To save this object to the database I do the following:

NewObjectServlet

//Create the object
LoanboardObject object = new LoanboardObject(objectId, etc...);

//Create the database
MongoDataTx tx = new MongoDataTx(DATABASE);
tx.save(object.toDBObject(), "object");

MongoDataTX

private DB db;

public MongoDataTx(String dbName) {
    db = Mongo.getMongoDB().getMongoClient().getDB(dbName);
}

public void save(final DBObject object, String collection) {
    DBCollection coll = db.getCollection(collection);
    coll.save(object);
}

Mongo

private static final String HOST = "localhost";
private static final int PORT = 27017;
private static Mongo mongoDB;
private static MongoClient mongo;

public Mongo() {
    try {
        mongo = new MongoClient(HOST, PORT);
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }
}

public static Mongo getMongoDB() {
    if (mongoDB == null) {
        mongoDB = new Mongo();
    }
    return mongoDB;
}

public MongoClient getMongoClient() {
    return mongo;
}

The problem with this is when a value is Null, the key-value pair it's still added to the database (but that's not nececary). One way to solve this is to make checks to see if the values aren't Null.

if(id != null){
    object.put("_id", id);
}

But is it possible to give mongodb settings so it ignores key-value pairs with the value Null? basicly same as here but than with Java.

Or should i use a function to add these values
something like this

public BasicDBObject toDBObject() {
    addElementToObject("_id", id, object);
    addElementToObject("object_name", objectName, object);
    addElementToObject("object_code", objectCode, object);
    addElementToObject("category", category, object);
    ...
}

private <T> void addElementToObject(String key, T value, BasicDBObject object) {
    if (value != null) {
        object.put(key, value);
    }
}

Possible dubplication

score 0 · Accepted Answer · answered May 01 '14 at 13:29

No, there's no way to tell MongoDB (or the Java driver) to ignore null values - nulls are considered valid input.

In the new Java driver, there might be a helper that will do the null check for you which won't add the field if the value is null. The new driver doesn't have a release date yet, so for now the best thing for you to do is check for null values yourself.

But, if you're only ever using Java to talk to your database, adding a null value for the field or ignoring the field and not writing it at all is exactly the same - the value in your LoanboardObject will still be null, it's not the same as a dynamic language where you can avoid having the field at all. Sure, you'll save a bit of space in the database by not saving null values, but you'll increase the complexity of your code for very little value.

How to delete the key/value pair when the Value is of type "Null" (on update)

1 Answers1