*Problem summary:*
When mapping "diamond shaped" OneToMany relationships using FetchType.EAGER and FetchMode.JOIN, Hibernate generates N+1 select statements. Here is what I mean with "diamond shape":
!Diamond.jpg|thumbnail!
*Expected behavior:*
A single select statement with two joins on the "BOTTOM" table.
*Actual behavior:*
{code:sql}
SELECT top0_.id AS id1_3_0_,
left1_.parent AS parent2_1_1_,
left1_.id AS id1_1_1_,
left1_.id AS id1_1_2_,
left1_.parent AS parent2_1_2_,
bottom2_.parent AS parent2_0_3_,
bottom2_.id AS id1_0_3_,
bottom2_.id AS id1_0_4_,
bottom2_.parent AS parent2_0_4_,
right3_.parent AS parent2_2_5_,
right3_.id AS id1_2_5_,
right3_.id AS id1_2_6_,
right3_.parent AS parent2_2_6_
FROM Top top0_
LEFT OUTER JOIN Left left1_
ON top0_.id = left1_.parent
LEFT OUTER JOIN Bottom bottom2_
ON left1_.id = bottom2_.parent
LEFT OUTER JOIN Right right3_
ON top0_.id = right3_.parent
WHERE top0_.id = ?
SELECT bottom0_.parent AS parent2_0_0_,
bottom0_.id AS id1_0_0_,
bottom0_.id AS id1_0_1_,
bottom0_.parent AS parent2_0_1_
FROM Bottom bottom0_
WHERE bottom0_.parent = ?
{code}
*Detailed explanation and code sample:*
https://stackoverflow.com/q/51199440/3216347
*Test Case:*
I am currently working on a test case https://github . I will update this ticket as soon as possible. com/hibernate/hibernate-orm/pull/2402 |
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