Using ObjectId as String in Java (Manual reference) with spring-data mongodb

Question

In MongoDB documentation they suggest to use ObjecId for manual references. please see https://docs.mongodb.com/manual/reference/database-references/#document-references

original_id = ObjectId()

db.places.insert({
    "_id": original_id,
    "name": "Broadway Center",
    "url": "bc.example.net"
})

db.people.insert({
    "name": "Erin",
    "places_id": original_id,
    "url":  "bc.example.net/Erin"
})

I'm using spring-data-mongodb and what I'm looking for is to have a People class defined like this:

@Document
public class People {

    private String name;
    @Reference // or any Annotation to convert an ObjectId to a String
    private String placesId; 
    private String url;
}

How to have a "places_id" as ObjectId in mongoDB but mapped to a String in our POJO ?

I was expecting to have an annotation like @Reference but it seems to not be implemented.

I don't understand why we don't have this kind of annotation in spring-data-mongodb. I don't want to implement an explicit converter like suggested in spring documentation for all documents that use manual references. Maybe it's not the right approach.

Did I miss something ?

UPDATE :

I like the idea to have a POJO using only String instead of ObjectId. Let's say I've got a class Place like this :

@Document
public class Place {
  @Id
  private String id;
  private String name;
}

place.getId() will be a String but people.getPlaceId() will be an ObjectId. I want to avoid this unnecessary mapping.

Answer 1

If you want to make a real reference to an other object in your database, use the @DBRef annotation which is provided by Spring Data .

Your updated code could look like the following:

@Document
public class People {

    private String name;

    @DBRef
    private Place place; 
    private String url;
}

Spring Data will then automatically map a Place object to your People object. Internally this is done with a reference to the unique ObjectId . Try this code and have a look at your mongo database.

For more information have a look at: MongoDb with java foreign key

Answer 2

Why don't you leave the field as ObjectId?

@Document
public class People {

    private String name;
    private ObjectId placesId; 
    private String url;
}

If you want to query by this field you can do this:

• For lists

  List<String> ids // the ids as strings List<ObjectId> objIds = ids .stream() .map(i -> new ObjectId(i)) .collect(Collectors.toList());

• For single String

  String id // single id ObjectId objId = new ObjectId(id);

Answer 3

The solution would be:

import org.springframework.data.mongodb.core.mapping.Field;
import org.springframework.data.mongodb.core.mapping.FieldType;

public class People {

    @Field(targetType = FieldType.OBJECT_ID)
    private String placesId; 
}

This will map POJO string to ObjectId in MongoDB.

Answer 4

I have a solution very simple:

@JsonSerialize(using= ToStringSerializer.class)
private ObjectId brandId;
...

put that on the attribute that is Object Id, and the ObjectId gets and inserts like string