JPA fetch join 문제점

• 이미지 중복 문제점

select
    post0_.id as id1_3_0_,
    postimages1_.id as id1_4_1_,
    posttags2_.id as id1_5_2_,
    tag3_.id as id1_6_3_,
    couple4_.id as id1_0_4_,
    post0_.created_date_time as created_2_3_0_,
    post0_.updated_date_time as updated_3_3_0_,
    post0_.content as content4_3_0_,
    post0_.couple_id as couple_i9_3_0_,
    post0_.dating_date as dating_d5_3_0_,
    post0_.latitude as latitude6_3_0_,
    post0_.longitude as longitud7_3_0_,
    post0_.title as title8_3_0_,
    postimages1_.image_url as image_ur2_4_1_,
    postimages1_.post_id as post_id3_4_1_,
    postimages1_.post_id as post_id3_4_0__,
    postimages1_.id as id1_4_0__,
    posttags2_.post_id as post_id2_5_2_,
    posttags2_.tag_id as tag_id3_5_2_,
    posttags2_.post_id as post_id2_5_1__,
    posttags2_.id as id1_5_1__,
    tag3_.color as color2_6_3_,
    tag3_.couple_id as couple_i4_6_3_,
    tag3_.name as name3_6_3_,
    couple4_.created_date_time as created_2_0_4_,
    couple4_.updated_date_time as updated_3_0_4_,
    couple4_.start_date as start_da4_0_4_
from
    post post0_
        inner join
    post_image postimages1_
    on post0_.id=postimages1_.post_id
        inner join
    post_tag posttags2_
    on post0_.id=posttags2_.post_id
        inner join
    tag tag3_
    on posttags2_.tag_id=tag3_.id
        inner join
    couple couple4_
    on post0_.couple_id=couple4_.id
where
        post0_.id=?

• 태그는 중복 제거가 되지만 이미지는 제거가 안되는 모습

• 사실 태그는 set이라 중복제거가 가능한 것

• 이미지는 list라 중복이 발생하게 된다.

• 이미지도 Set으로 변경한다면?

• 중복없이 둘 다 가져온다.

• 하지만 이미지는 썸네일 이미지를 조회할 수 있어야 하기 때문에 순서가 중요하다.

• 결국

select
        post0_.id as id1_3_0_,
        posttags1_.id as id1_5_1_,
        tag2_.id as id1_6_2_,
        couple3_.id as id1_0_3_,
        post0_.created_date_time as created_2_3_0_,
        post0_.updated_date_time as updated_3_3_0_,
        post0_.content as content4_3_0_,
        post0_.couple_id as couple_i9_3_0_,
        post0_.dating_date as dating_d5_3_0_,
        post0_.latitude as latitude6_3_0_,
        post0_.longitude as longitud7_3_0_,
        post0_.title as title8_3_0_,
        posttags1_.post_id as post_id2_5_1_,
        posttags1_.tag_id as tag_id3_5_1_,
        posttags1_.post_id as post_id2_5_0__,
        posttags1_.id as id1_5_0__,
        tag2_.color as color2_6_2_,
        tag2_.couple_id as couple_i4_6_2_,
        tag2_.name as name3_6_2_,
        couple3_.created_date_time as created_2_0_3_,
        couple3_.updated_date_time as updated_3_0_3_,
        couple3_.start_date as start_da4_0_3_ 
    from
        post post0_ 
    inner join
        post_tag posttags1_ 
            on post0_.id=posttags1_.post_id 
    inner join
        tag tag2_ 
            on posttags1_.tag_id=tag2_.id 
    inner join
        couple couple3_ 
            on post0_.couple_id=couple3_.id 
    where
        post0_.id=?

select
        postimages0_.post_id as post_id3_4_1_,
        postimages0_.id as id1_4_1_,
        postimages0_.id as id1_4_0_,
        postimages0_.image_url as image_ur2_4_0_,
        postimages0_.post_id as post_id3_4_0_ 
    from
        post_image postimages0_ 
    where
        postimages0_.post_id=?

• List 반환이 아니라서 자동으로 중복 제거하여 반환해주는 것 같다.
• List로 반환한다면?



• DISTINCT 적용 시

• Hibernate default_batch_fetch_size 처음엔 해당 옵션으로 해결하려 했지만 생각해보니 in절로 날리는 것이 아닌 =절로 쿼리를 수행하면 되서 필요없는 옵션이였다

[JPA] Fetch Join 할 때 MultipleBagFetchException 해결하는 법

이번 글에서는 JPA 를 사용한지 얼마 안된 초보자 입장에서 겪은 어려움을 공유하고 어떻게 해결해나갔는지 공유하며 생각을 정리해보려 합니다. 위의 화면에 대한 API를 만들어야 하는 상황입니다. 위의 뷰에서는 내가 팔로우 하고 있는 사람이 작성한 게시글 이 나타나야 합니다. View를 보면서 DB Table 을 간단하게 같이 보겠습니다.

https://devlog-wjdrbs96.tistory.com/421

A Guide to MultipleBagFetchException in Hibernate | Baeldung

In this tutorial, we'll talk about the MultipleBagFetchException. We'll begin with the necessary terms to understand, and then we'll explore some workarounds until we reach the ideal solution. We'll create a simple music app's domain to demonstrate each of the solutions. A Bag, similar to a List, is a collection that can contain duplicate elements.

https://www.baeldung.com/java-hibernate-multiplebagfetchexception