How to get the ObjectId value from MongoDB?

Question

I'm using Jongo with Play framework 2, java. I added some data into my MongoDB.

{"_id" : ObjectId("538dafffbf6b562617252178"), ... }

However, when I fetched the ObjectId from the database, it gave me like:

de.undercouch.bson4jackson.types.ObjectId@484431ff instead of 538dafffbf6b562617252178. I don't quite understand how can I get the ObjectId value. My class is defined as following:

public class Product {
    @JsonProperty("_id")
    protected String id;
    ...
    public Product() {
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }
}

EDIT

In order to fetch the data, I simply use find() function provided by Jongo as following:

public static Iterable<Product> findAll(){
    return products().find().as(Product.class);
}

Did you try fetching it using the key value ie cursor.get("_id").valueOf() ? — AppleBud, Jun 05 '14 at 08:55
@AppleBud I used `find()` method to fetch the data. Please see my edited question. — lvarayut, Jun 05 '14 at 08:58

score 1 · Answer 1 · answered Jun 05 '14 at 09:22

Your ObjectId is of type de.undercouch.bson4jackson.types.ObjectId. By looking at the source you can see that there isn't a toString method defined on that class, so the default toString implementation is used instead.

MongoDB's ObjectId is actually 12-bit BSON type that's constructed using:

a 4-byte value representing the seconds since the Unix epoch,
a 3-byte machine identifier,
a 2-byte process id, and
a 3-byte counter, starting with a random value.

The class your are using is built a little bit different - it's internally stored as 3 integers. It has public getTime, getMachine and getInc methods so you can create your own using those values. Something like this will probably get you what you want:

(id.getTime() + id.getMachine() + ide.GetInc()).toHexString()

score 1 · Accepted Answer · answered Jun 06 '14 at 08:25

1

id field annotated with @JsonProperty("_id") just means that your product documents have custom ids (ie. setted by user eg: 1234, 5678, ...)

You should annotate id field with both @Id and @ObjectId annotations to tell Jongo to handle id field as a real ObjectId managed by MongoDB.

public class Product {

@org.jongo.marshall.jackson.oid.Id
@org.jongo.marshall.jackson.oid.ObjectId
protected String id;
...
  public Product() {
  }
}

During deserialization, a string representation of ObjectId will be setted into Product instances

answered Jun 06 '14 at 08:25

Benoît Guérout

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Thanks for your response. I tried what you mentioned above, however, it gave me `Execution exception[[RuntimeException: java.lang.IllegalArgumentException: invalid ObjectId [de.undercouch.bson4jackson.types.ObjectId@6e07e6fc] (through reference chain: java.util.ArrayList[0]->models.Product["_id"])]]` – lvarayut Jun 11 '14 at 11:34
You should open an issue https://github.com/bguerout/jongo/issues and provide the full stack trace. This question will be updated later with what we have found. – Benoît Guérout Jun 12 '14 at 19:00

How to get the ObjectId value from MongoDB?

2 Answers2