Spring Data Jpa & Hibernate

Technologies

• Spring Data JPA
• Hibernate
• H2

Description

In this repo, you can find the same query findAll using different approaches in order to manipulate the fetch plan of the query

Goal

This repo is used to demonstrate the different behaviours of JPA/Hibernate when loading a single Entity and its relations or a List of Entities and their relations, and understand the differences and the defaults

How to start the application

mvn spring-boot:run

Examples

findAll using JPA Criteria to enable the fetch join for the relations

curl http://localhost:8080/user/predicate

Hibernate: select user0_.id as id1_1_0_, userdetail1_.id as id1_21_, contactdet2_.id as id1_0_2_, user0_.contact_details_id as contact_3_1_0_, user0_.name as name2_1_0_, userdetail1_.nationality as national2_2_1_, userdetail1_.user_id as user_id3_2_1_, contactdet2_.email as email2_0_2_, contactdet2_.mobile as mobile3_0_2_ 
from user user0_ 
left outer join user_details userdetail1_ on user0_.id=userdetail1_.user_id 
left outer join contact_details contactdet2_ on user0_.contact_details_id=contactdet2_.id

findAll using NamedEntityGraphs to specify the fetch plan

curl http://localhost:8080/user/all

Hibernate: select user0_.id as id1_1_0_, contactdet1_.id as id1_0_1_, userdetail2_.id as id1_2_2_, user0_.contact_details_id as contact_3_1_0_, user0_.name as name2_1_0_, contactdet1_.email as email2_0_1_, contactdet1_.mobile as mobile3_0_1_, userdetail2_.nationality as national2_2_2_, userdetail2_.user_id as user_id3_2_2_ 
from user user0_ 
left outer join contact_details contactdet1_ on user0_.contact_details_id=contactdet1_.id 
left outer join user_details userdetail2_ on user0_.id=userdetail2_.user_id

... you can also change the name of the EntityGraph that is being used in the UserRepository to @EntityGrah("withUserDetails") and see the difference

findAll without any customization

Go to the UserRepository and comment the @EntityGraph("withAllDetails")

    //@EntityGraph("withAllDetails")
    List<User> findAll();

Restart the application

curl http://localhost:8080/user/all

Hibernate: select user0_.id as id1_1_, user0_.contact_details_id as contact_3_1_, user0_.name as name2_1_ from user user0_
Hibernate: select contactdet0_.id as id1_0_0_, contactdet0_.email as email2_0_0_, contactdet0_.mobile as mobile3_0_0_ from contact_details contactdet0_ where contactdet0_.id=?
Hibernate: select userdetail0_.id as id1_2_2_, userdetail0_.nationality as national2_2_2_, userdetail0_.user_id as user_id3_2_2_, user1_.id as id1_1_0_, user1_.contact_details_id as contact_3_1_0_, user1_.name as name2_1_0_, contactdet2_.id as id1_0_1_, contactdet2_.email as email2_0_1_, contactdet2_.mobile as mobile3_0_1_ from user_details userdetail0_ left outer join user user1_ on userdetail0_.user_id=user1_.id left outer join contact_details contactdet2_ on user1_.contact_details_id=contactdet2_.id where userdetail0_.user_id=?
Hibernate: select contactdet0_.id as id1_0_0_, contactdet0_.email as email2_0_0_, contactdet0_.mobile as mobile3_0_0_ from contact_details contactdet0_ where contactdet0_.id=?
Hibernate: select userdetail0_.id as id1_2_2_, userdetail0_.nationality as national2_2_2_, userdetail0_.user_id as user_id3_2_2_, user1_.id as id1_1_0_, user1_.contact_details_id as contact_3_1_0_, user1_.name as name2_1_0_, contactdet2_.id as id1_0_1_, contactdet2_.email as email2_0_1_, contactdet2_.mobile as mobile3_0_1_ from user_details userdetail0_ left outer join user user1_ on userdetail0_.user_id=user1_.id left outer join contact_details contactdet2_ on user1_.contact_details_id=contactdet2_.id where userdetail0_.user_id=?
Hibernate: select userdetail0_.id as id1_2_2_, userdetail0_.nationality as national2_2_2_, userdetail0_.user_id as user_id3_2_2_, user1_.id as id1_1_0_, user1_.contact_details_id as contact_3_1_0_, user1_.name as name2_1_0_, contactdet2_.id as id1_0_1_, contactdet2_.email as email2_0_1_, contactdet2_.mobile as mobile3_0_1_ from user_details userdetail0_ left outer join user user1_ on userdetail0_.user_id=user1_.id left outer join contact_details contactdet2_ on user1_.contact_details_id=contactdet2_.id where userdetail0_.user_id=?