Sounds like conflating layers to me… your request has nullable fields; your domain model does not

# jackson-kotlin

[mp]

Sounds like conflating layers to me… your request has nullable fields; your domain model does not

[rrader]

yes, request has nulls, and I want in response to write that baz and bar fields are required

[rrader]

But Kotlin throw an execption when pass null to not nullable, so we fail at first field, and can write only about 1 field at once

[rrader]

the desired result will be to write about both fields

[diesieben07]

Non-Nullable types are not for user-input validation. If there is a possibility that null can come in from the outside world, the type in kotlin must be nullable. Validation is a separate step.

[rrader]

if field is nullable, I will have to check field if it is not null everytime I want to use it, but it was already validated at some step

[diesieben07]

Yes, unfortunately Kotlin's type system is not as rich as e.g. TypeScript's. That would allow you express something like that

[diesieben07]

The way to do it would be to have two versions of your data classes, one that is not validated and one that is validated.
Then you can also introduce domain classes like Email.

[rrader]

Do you have an example of TypeScript in such cases?

[rrader]

I don't want 2 classes, why is it not ok to disable null checks in this only for module with such classes, in these classes validation is done by framework and will guarantee that fields will not be null

[diesieben07]

Typescript example:

type Foo<T> = {
    baz: string | T
    bar: number | T
}

type FooUnvalidated = Foo<null>
type FooValidated = Foo<never>

function validate(input: FooUnvalidated): FooValidated {
    const {baz, bar} = input;
    if (baz === null) throw Error();
    if (bar === null) throw Error();
    return {
        baz, bar
    }
}

const input: FooUnvalidated = {baz: null, bar: 123};
const validated = validate(input);
const bar: number = validated.bar;
const doesntWork: number = input.bar; // does not compile, input.bar could be null