Builder pattern when retrieving entity from DB w/ spring boot reactor & mongo

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I have the following bean that describes a mongo document, and that uses lombok:

@JsonDeserialize(builder = MyClass.MyClassBuilder.class)
@Builder(toBuilder = true)
@Value
public class MyClass {

    private final String id;

    @Default
    private final String field = "defaultValue";

    @JsonPOJOBuilder(withPrefix = "")
    public static class MyClassBuilder {}
}

When deserializing {"id": "document"} with jackson, I end-up with a bean containing both id=document and field=defaultValue because it used the builder that provide a default value for the field.

Now what I want to do, is to have the defaultValue set for documents coming out of the database (coming from ReactiveMongoTemplate). But it seems to use the all args constructor even if I set it private (or some reflect black magic)

So the main question is: is it possible to tell spring to use the builder to build the bean when coming out of the database?

spring-mongodb spring-boot lombok spring java
1 Answers

  • You are not going to be able to use your custom serialiser because when I go through the source code of MappingMongoConverter in spring mongodb (debugged it with a sample app) , I see only the following steps.

  • Once the value from db is available as org.bson.Document, MappingMongoConverter.java is looking to create your entity object.

  • First, it checks if you have any custom converters registered and if you have it, then use it. So one option is to use a custom converter registered.

  • If there is no custom converters registered, it goes and find the PersistenceConstructor and use it. I had an object with 3 constructors (no param, one param, and all param) and it chose my no param constructor.

  • However, if I annotate a constructor with @PersistenceConstructor, it is choosing that constructor. So could follow this approach but then you have to keep String field un-initialised and getting initialised differently in each constructor

  • MappingMongoConverter.java

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