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.

dma_k · Accepted Answer · 2021-06-08 19:31:25Z

8

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.

answered Jun 8, 2021 at 19:31

dma_k

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4 Comments

Jignesh M. Khatri Over a year ago

What can be done if there is List<String> instead of String? I mean list of object Ids.

dma_k Over a year ago

Good question. I would probably raise a ticket for Spring Data MongoDB GitHub project, because somebody would ask for Set instead of List and so on.

Tarunjeet Singh Salh Over a year ago

@dma_k Any solution for List<String> ? I mean it's only 3 months but still gotta ask.

dma_k Over a year ago

I don't have any solution, you'd better ask Spring Data community. Probably one can hack by implementing a custom converter?

rieckpil · Accepted Answer · 2017-12-28 20:47:40Z

3

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

answered Dec 28, 2017 at 20:47

rieckpil

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Comments

Kevin Montalvo · Accepted Answer · 2020-03-22 04:16:35Z

3

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

answered Mar 22, 2020 at 4:16

Kevin Montalvo

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1 Comment

SledgeHammer Over a year ago

The only actually correct solution

Alex P. · Accepted Answer · 2017-12-28 20:35:11Z

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);

answered Dec 28, 2017 at 20:35

Alex P.

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3 Comments

Mathieu LECLAIRE Over a year ago

Thanks Alex. I've updated my question with more details because I would like to avoid this mapping. But what you're suggesting is working.

Alex P. Over a year ago

Unfortunately there is no specific annotation provided yet. Only field _id is handled in the mapping layer. When using the MappingMongoConverter there are certain rules that govern how properties from the Java class is mapped to this _id field

Alex P. Over a year ago

But you could look into customizing the MappingMongoConverter

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