How to (de)serialize custom ID object to String?

[jean-morissette]

Context
We are using DGS to generate POJO and store/retrieve them directly into Mongo database via DGS graphql web api.

Problem
We want to use Mongo ObjectId as ID in the generated POJO while exposing the ID as a string in the web api.
We should be able to use the method ObjectId.toHexString somewhere to convert ObjectId to String when the POJO is serialized to JSON before sending the response to the client.

Is it possible and if yes, any advices? Thanks in advance.

Example of our code with actual and expected result

GraphQL schema :

type Foo {
    id: ID
    ...
}

build.gradle.kts :

tasks.withType<com.netflix.graphql.dgs.codegen.gradle.GenerateJavaTask> {
    typeMapping = mutableMapOf(
            "ID" to "org.bson.types.ObjectId"
    )
}

generated types :

public class Foo {
  private ObjectId id;
  public ObjectId getId() {
    return id;
  }
  public void setId(ObjectId id) {
    this.id = id;
  }

actual web endpoint output :

{
  "data": {
    "getFoo": { 
      "id": { 
        "timestamp": 1640673996,  
        "counter": 9263472, 
        "randomValue1": 6782678,  
        "randomValue2": -2695  
      }
    }
  }
}

desired web endpoint output :

{
  "data": {
    "getFoo": { 
      "id": "61ca579a677ed6f5790f6e2a" 
    }
  }
}