如何在避免 n+1 查询的同时设置 JPA 双向一对一

Question

I'm trying to debug two entities that have a bi-directional one to one relationship. The problem is that the relationship is causing N+1 Queries to occur. When I run findAll() a single query is executed for every item in my table.

Here is an example: I have two entities

package ...;
import ...;

@AllArgsConstructor(access = AccessLevel.PRIVATE)
@NoArgsConstructor
@EqualsAndHashCode
@Getter
@Builder

@Entity
@Table(name = "tracker")
public class TrackerEntity {
    @Id
    @Column(name = "vehicleid")
    private UUID vehicleId;

    @Column(name = "trackerid")
    private String trackerId;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "vehicleid", referencedColumnName = "id")
    private VehicleEntity vehicleEntity;
}

@AllArgsConstructor(access = AccessLevel.PRIVATE)
@NoArgsConstructor
@EqualsAndHashCode
@Getter
@Builder

@Entity
@Table(name = "vehicle")
public class VehicleEntity {
    @Id
    private UUID id;

    @Column(name = "vehiclename")
    private String vehicleName;

    @OneToOne(mappedBy = "vehicleEntity", cascade = CascadeType.REMOVE, orphanRemoval = true)
    private TrackerEntity trackerEntity;
}

When I run vehicleRepository.findAll() I get following debug logs:

2022-05-17 19:16:45.071 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.097 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.104 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.106 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.109 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.110 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.113 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.115 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.117 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.119 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.123 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.125 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.128 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.130 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.133 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.135 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.138 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.141 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.144 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_0_, vehicleent0_.vehiclename as vehiclen2_1_0_ from vehicle vehicleent0_ where vehicleent0_.id=?
2022-05-17 19:16:45.146 DEBUG 62639 --- [           main] org.hibernate.SQL                        : insert into vehicle (vehiclename, id) values (?, ?)
2022-05-17 19:16:45.246 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select vehicleent0_.id as id1_1_, vehicleent0_.vehiclename as vehiclen2_1_ from vehicle vehicleent0_
2022-05-17 19:16:45.253 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.258 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.259 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.261 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.262 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.264 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.265 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.267 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.269 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?
2022-05-17 19:16:45.271 DEBUG 62639 --- [           main] org.hibernate.SQL                        : select trackerent0_.vehicleid as vehiclei1_0_0_, trackerent0_.trackerid as trackeri2_0_0_ from tracker trackerent0_ where trackerent0_.vehicleid=?

I've searched for N+1 JPA Query problems in hopes of finding a solution and most either suggested using EntityGraph or "bytecode enhancement". I've tried using entitygraph and still got n+1 queries and I don't want to use bytecode enhancement since the application has to run on a cloud as a microservice.

One more important thing is I want Trackers to be removed when their Vehicle is removed but they should not be created when a vehicle is created.

Is there any way to fix this?

I have tried using Query and join fetch:

public interface VehicleRepository extends JpaRepository<VehicleEntity, UUID> {

    @Override
    @Query("SELECT v FROM VehicleEntity v left outer join fetch v.trackerEntity t")
    <S extends VehicleEntity> List<S> findAll(Example<S> example);
}

which did not change anything, still got n+1 queries. I have tried EntityGraph which changed nothing as well:

@Entity
@Table(name = "vehicle")
@NamedEntityGraph(name="vehicleGraph", attributeNodes = {@NamedAttributeNode("trackerEntity")})
public class VehicleEntity {
    @Id
    private UUID id;

    @Column(name = "vehiclename")
    private String vehicleName;

    @OneToOne(mappedBy = "vehicleEntity", cascade = CascadeType.REMOVE, orphanRemoval = true)
    private TrackerEntity trackerEntity;
}

public interface VehicleRepository extends JpaRepository<VehicleEntity, UUID> {

    @Override
    @EntityGraph(value = "vehicleGraph", type = EntityGraph.EntityGraphType.LOAD)
    <S extends VehicleEntity> List<S> findAll(Example<S> example);
}

Answer 1

You can optimize this with EntityGraph and lazy loading. I presume VehicleEntity is the owning entity here. In that case make fetch = FetchType.LAZY and cascade = CascadeType.ALL should be on the owning entity. And EntityGraph can be defined 2 ways

1. Named Entity Graph
2. AD-HOC or Unnamed Entity Graph

Named Entity Graph:

you can define NamedEntityGraph on owning class and reference it in VehicleEntityRepository interface

@NamedEntityGraph(name = "VehicleEntity.trackerEntity", attributeNodes = @NamedAttributeNode("trackerEntity"))
public class VehicleEntity {
}

VehicleEntityRepository.java

public interface VehicleEntityRepository extends JpaRepository<VehicleEntity, UUID> {
     @EntityGraph(value = "VehicleEntity.trackerEntity", type = EntityGraphType.LOAD)
    List<VehicleEntity> findAll();
}

AD-HOC Entity Graph:

You don't have to define any EntityGraph annotation VehicleEntity class but can directly use it Repository interface

VehicleEntityRepository.java

public interface VehicleEntityRepository extends JpaRepository<VehicleEntity, UUID> {
    @EntityGraph(attributePaths = { "trackerEntity" })
    List<VehicleEntity> findAll();
}

VehicleEntity.java

@AllArgsConstructor(access = AccessLevel.PRIVATE)
@NoArgsConstructor
@EqualsAndHashCode
@Getter
@Builder

@Entity
@Table(name = "vehicle")
@NamedEntityGraph(name = "VehicleEntity.trackerEntity", attributeNodes = @NamedAttributeNode("trackerEntity"))
public class VehicleEntity {
    @Id
    private UUID id;

    @Column(name = "vehiclename")
    private String vehicleName;

 
@OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "vehicleEntity")
    @JsonManagedReference
    private TrackerEntity trackerEntity;
}

TrackerEntity.java

package ...;
import ...;

@AllArgsConstructor(access = AccessLevel.PRIVATE)
@NoArgsConstructor
@EqualsAndHashCode
@Getter
@Builder

@Entity
@Table(name = "tracker")
public class TrackerEntity {
    @Id
    @Column(name = "id")
    private UUID id;

    @Column(name = "trackerid")
    private String trackerId;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "vehicleid", referencedColumnName = "id")
@JsonBackReference
    private VehicleEntity vehicleEntity;
}
    

You can also use @JsonManagedReference and @JsonBackReference to prevent nested fetch or infinite recursion when using Jackson.