Documentation of why Kotlin JDSL returns a nullable list in the Spring Support module.

[progress0407]

Motivation

• This PR on the subject

Modifications

• wrote why-kotlin-jdsl-returns-nullable-list-in-the-spring-support-module.md document.

Result

• As described in the topic above(Modifications)

Closes

• Documentation of why Kotlin JDSL returns a nullable list in the Spring Support module. #667

[progress0407]

hello!
I think the original date I was going to do the work and post the PR was 3.27~28th...
I apologize for posting it now, and thank you for your help.

[shouwn]

Thanks for your help! I think the confirmation of this PR will be delayed for a week or two.

[progress0407]

Thank you. I'm sure you've been busy deploying version 3.4.0 otherwise. I understand. 🥰

[cj848]

This is inaccurate information. In case of DTO Projection, Nullable is also allowed. For example

class Entity {
   @Id
   var id: Long? = null

   @Column(nullable = true)
   var name: String? = null
}

class DTO {
  var name: String?
}

When there is an entity like the above, null may occur at the time of the query below.

select new DTO(name) from Entity;

[shouwn]

This is correct information. When using the new keyword in JPQL, the constructor is called for every row to create the object. That's why there can't be a nullable for DTO Projection only.

[cj848]

If you mean returning a DTO object itself, that is correct.
I meant that the fields in the object are nullable, but that seems to be incorrect information. Thanks for the good point.

[progress0407]

Ah, I see you got it, I'll add it to the documentation!

[progress0407]

It's nice to be able to check it with test code.

[progress0407]

Thank you so much for the review! We will reflect it sequentially after checking :)

[shouwn]

This is correct information. When using the new keyword in JPQL, the constructor is called for every row to create the object. That's why there can't be a nullable for DTO Projection only.

[shouwn]

메타데이터 모델 생성은 nullable 주제와는 연관이 적어 보입니다.

'Type Safe하게 쿼리를 작성할 수 있게 도와주지만, 왜 리스트 반환 시에는 non-null한 것도 nullable하게 반환하는지 궁금하실 수 있다' 는 스토리로 글을 풀어가면 좋을 것 같습니다.

[progress0407]

음 확실히 저번에 올린 PR(메타 모델)과는 성격이 다른 것 같아요. 수정하겠습니다!

[progress0407]

Thank you for your review!
I reflected!

[cj848]

Suggested change

	| DTO Projection | X | 모든 ROW에 대한 생성자 호출하기 때문에 객체가 생성되어 null을 허용하는 결과가 나오지 않음<br/>DTO의 필드가 null일 수는 있으나 DTO 객체가 null일 수는 없음 |
	| DTO Projection | X | 모든 ROW에 대한 생성자를 호출하기 때문에 객체가 생성되어 null을 허용하는 결과가 나오지 않음<br/>DTO의 필드가 null일 수는 있으나 DTO 객체가 null일 수는 없음 |

i think this is correct.

[progress0407]

Thank you for the detailed review! I will edit it. ☺️

[shouwn]

I apologize for the delay in reviewing, I've been busy with other things.

Thanks for your help. I'll make some changes to the documentation later!

[progress0407]

Oh, no, I know it's not easy to take the time to review outside of work hours. I always appreciate your reviews!