Java: Rethink Domain Primitives with Valhalla - hckrnws

hckrnws

Java: Rethink Domain Primitives with Valhalla

(dfa1.github.io)

31

11

4d

by dfa11

exabrial

53d

> Value classes cannot be null.

Won't this be an issue for JPA/JSONB? `null` is a an important and value in JSON and nearly every database, and for modeling the real world.

dfa11 • OP

03d

True: this compiles and the test passes today on JDK 27-jep401ea3:

  record Person(String name, Age age, Iban iban) {}

  // {"name": "SuperMario", "age": null, "iban": null}
  Person result = mapper.readValue(json, Person.class);

  assertThat(result.age()).isNull();   // passes — value class field, null
  assertThat(result.iban()).isNull();  // passes — value class field, null

  Jackson bypasses the constructor for null JSON tokens (getNullValue() short-circuits), so the
  validation in new Age(...) never runs. Both Age and Iban are value classes; both fields are null.

What do you think? Of course, there are limitations as Person cannot be flattened anymore but I guess Valhalla will ship more JEPs later?

mrkeen
33d
It is not.
Null is the thing which it isn't. A null value is evidence that your modelling does not fit the domain.
1. exabrial
  23d
  Unfortunately, the simple fact is that one can be handed a JSON document with non-existent keys, and one can be handed a database row with a null column. Often, the programmer may handed a schema from a third party they have no control over: opening a semantics debate is likely not a good course of action.
  I guess since basic types, like an int or double, cannot be null, I understand why these cannot be null. This unfortunately limits their usefulness, but it's a carryover from the underlying properties of the basic type.