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> 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 th

> 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.

mrkeen 5mo ago
It is not. Null is the thing which it isn't. A null value is evidence that your modelling does not fit the domain.
- exabrial 5mo ago
  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.
  - mrkeen 5mo ago
    I agree that it is unfortunate.
  - joe_mwangi 5mo ago
    Value types will be optionally null. What java will introduce to the tooling is narrowing of nullness types. Hence Foo! <: Foo? <: Foo. This will assist in enabling safe domains or scope in code that are null-restricted with ease. Hence we can model around such a type system rule.
dfa11 5mo ago
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?

> 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.

mrkeen 5mo ago

It is not. Null is the thing which it isn't. A null value is evidence that your modelling does not fit the domain.

exabrial 5mo ago
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.
- mrkeen 5mo ago
  I agree that it is unfortunate.
- joe_mwangi 5mo ago
  Value types will be optionally null. What java will introduce to the tooling is narrowing of nullness types. Hence Foo! <: Foo? <: Foo. This will assist in enabling safe domains or scope in code that are null-restricted with ease. Hence we can model around such a type system rule.

dfa11 5mo ago

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?