liangbodeng/unnecessary-flush-on-dirty

Demo of unnecessary onFlushDirty() invoked on the parent entity in a @OneToOne relationship

This project was created to demonstrate a behavior change in Hibernate 5.6 comparing to Hibernate 5.4: if a @OneToOne field in a parent entity is changed, it will trigger an unnecessary onFlushDirty() to the parent entity, even though none of its columns was changed.

Description

For example, assuming we have two entities with @OneToOne relationship: User and Profile, and User is the parent entity.

Entity	Table
User(id, version, profile)	users(id, version)
Profile(id, user)	profile(id, user_id)

Scenario: user1 previously had profile=null, and now we create profile1 and link it to user1 and save profile1.

Expected: onFlushDirty() should not be invoked on user1.

Actual: onFlushDirty() was invoked on user1.

Run the test case

• To see the Hibernate 5.6.x behavior, run following command, and check the output

  ./gradlew clean test --info

  ======== START ========
  Hibernate: insert into users (version, id) values (?, ?)
  Hibernate: select user0_.id as id1_1_0_, user0_.version as version2_1_0_, profile1_.id as id1_0_1_, profile1_.user_id as user_id2_0_1_ from users user0_ left outer join profile profile1_ on user0_.id=profile1_.user_id where user0_.id=?
  onFlushDirty invoked on a User
  Hibernate: insert into profile (user_id, id) values (?, ?)
  Hibernate: update users set version=? where id=?
  ========= END =========
  

• To see the Hibernate 5.4.x behavior (with a local org.hibernate.type.OneToOneType class)

  ./gradlew clean test --info -Phibernate54=true

  ======== START ========
  Hibernate: insert into users (version, id) values (?, ?)
  Hibernate: select user0_.id as id1_1_0_, user0_.version as version2_1_0_, profile1_.id as id1_0_1_, profile1_.user_id as user_id2_0_1_ from users user0_ left outer join profile profile1_ on user0_.id=profile1_.user_id where user0_.id=?
  Hibernate: insert into profile (user_id, id) values (?, ?)
  ========= END =========