MongoDB and java - CodecRegistry only returning an ID field rather than all fields in POJO?

I have the following code to create my mongo client in my Java Spring project:

CodecRegistry pojoCodecRegistry = fromRegistries(MongoClientSettings.getDefaultCodecRegistry(),
        fromProviders(PojoCodecProvider.builder().register(Person.class).automatic(true).build()));

MongoClientSettings settings = MongoClientSettings.builder()
        .codecRegistry(pojoCodecRegistry)
        .applyConnectionString(new ConnectionString("myConnectionStrng"))
        .build();

MongoClient mongoClient = MongoClients.create(settings);
MongoDatabase database = mongoClient.getDatabase("person").withCodecRegistry(pojoCodecRegistry);
MongoCollection<Person> collection = database.getCollection("personCollection", Person.class).withCodecRegistry(pojoCodecRegistry);

My Kotilin Pojo is:

@JsonInclude(JsonInclude.Include.NON_NULL)
class Person {

    @JsonProperty("_id")
    var personID: String? = null

    @JsonProperty("name")
    var type: String? = null

    @JsonProperty("age")
    var age: Int? = null
	
}

I am able to get a response but the response is not as expected, i.e. it is

{
  "persons": [
    {
      "ID": "personId1"
    },
    {
      "ID": "personId2"
    },
    {
      "ID": "personId3"
    }
}

Each person object only shows some ID field rather than the fields in my POJO that I am expecting.

What am I missing here? Do I need to define a custom codec for my Pojo? I am unsure as first time using this mongo library.

Below is some working code where you can see that I write to the DB and read back data.

Several things are not clear in your question which may either explain why your attempt did not work, or I have misunderstood your requirement.

Person class

Person is a POJO - for this you probably don't want to use a straight class. In the way created it is awkward to construct the Person - I had to create a little helper method as there is no constructor in your class:

private static Person makePerson(String id, String type, int age) {
    Person p = new Person();
    p.setPersonID(id);
    p.setType(type);
    p.setAge(age);
    return p;
}

Whereas, if you make a few small alterations and use a data class then this implicitly gives you a constructor, toString(), hashCode():

@JsonInclude(JsonInclude.Include.NON_NULL)
data class Person (     //<< round brackets

    @JsonProperty("_id")
    var personID: String? = null,  //<< comma

    @JsonProperty("name")
    var type: String? = null,

    @JsonProperty("age")
    var age: Int? = null,

)

Codec setup

I don't think you have your Codecs setup in the right way. (If a Codec is missing you will get a startup error.). Observe my working code.

What is your intended output?

You say it is "not as expected", is it that it is missing the age and name/type field? The field name is "ID" too, what do you want? personID, _id or ID ?

How is your output implemented now?

How are you extracting and displaying the data in JSON - you don't say but given the annotations you use (@JsonProperty), you must be using Jackson, I have included that in my code sample. The Quick Start Guide you refer to talks about @BsonProperty - this is for a different purpose - for how to name the fields in the database, where as @JsonProperty is for naming in JSON.

Specimen code

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mongodb.ConnectionString;
import com.mongodb.MongoClientSettings;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.codecs.configuration.CodecRegistry;
import org.bson.codecs.pojo.PojoCodecProvider;

import java.util.ArrayList;
import java.util.List;

import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
import static org.bson.codecs.configuration.CodecRegistries.fromRegistries;

public class Test {

    public static void main(String[] args) {
        ConnectionString connectionString = new ConnectionString("mongodb://127.0.0.1:27017");
        CodecRegistry pojoCodecRegistry = fromProviders(PojoCodecProvider.builder().automatic(true).build());
        CodecRegistry codecRegistry = fromRegistries(MongoClientSettings.getDefaultCodecRegistry(), pojoCodecRegistry);
        MongoClientSettings clientSettings = MongoClientSettings.builder()
                .applyConnectionString(connectionString)
                .codecRegistry(codecRegistry)
                .build();
        try (MongoClient mongoClient = MongoClients.create(clientSettings)) {
            MongoDatabase database = mongoClient.getDatabase("person");
            MongoCollection<Person> collection = database.getCollection("personCollection", Person.class);

            List<Person> persons = new ArrayList<>();
            persons.add(makePerson("personId1", "Lesley", 10));
            persons.add(makePerson("personId2", "Bob", 20));
            persons.add(makePerson("personId3", "Jane", 30));

            collection.insertMany(persons);

            List<Person> persons2 = collection.find().into(new ArrayList<Person>());
            ObjectMapper mapper = new ObjectMapper();
            System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(persons2));

        } catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }

    private static Person makePerson(String id, String type, int age) {
        Person p = new Person();
        p.setPersonID(id);
        p.setType(type);
        p.setAge(age);
        return p;
    }
}

And the output is:

[ {
  "_id" : "personId1",
  "name" : "Lesley",
  "age" : 10
}, {
  "_id" : "personId2",
  "name" : "Bob",
  "age" : 20
}, {
  "_id" : "personId3",
  "name" : "Jane",
  "age" : 30
} ]

And the dependencies I used:

        <dependency>
            <groupId>org.mongodb</groupId>
            <artifactId>mongodb-driver-sync</artifactId>
            <version>4.8.1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.14.0</version>
        </dependency>