我正在嘗試除錯兩個具有雙向一對一關系的物體。問題是這種關系導致 N 1 查詢發生。當我findAll()對表中的每個專案執行單個查詢時。
這是一個例子：我有兩個物體
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;
}
當我運行時，vehicleRepository.findAll()我得到以下除錯日志：
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=?
我搜索了 N 1 JPA 查詢問題，希望能找到解決方案，大多數建議使用 EntityGraph 或“位元組碼增強”。我試過使用物體圖，但仍然有 n 1 個查詢，我不想使用位元組碼增強，因為應用程式必須作為微服務在云上運行。
更重要的一件事是我希望在洗掉車輛時洗掉跟蹤器，但不應該在創建車輛時創建它們。
有沒有什么辦法解決這一問題？
我嘗試過使用 Query 并加入 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);
}
它沒有改變任何東西，仍然有 n 1 個查詢。我試過 EntityGraph 也沒有改變：
@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);
}
uj5u.com熱心網友回復：
您可以使用EntityGraph延遲加載來優化它。我認為VehicleEntity是這里的擁有物體。在這種情況下，制作fetch = FetchType.LAZY并且cascade = CascadeType.ALL應該在擁有物體上。EntityGraph可以定義2種方式
- 命名物體圖
- AD-HOC 或未命名物體圖
命名物體圖：
您可以NamedEntityGraph在擁有類上定義并在VehicleEntityRepository界面中參考它
@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 物體圖：
您不必定義任何 EntityGraph 注解 VehicleEntity 類而可以直接使用它的 Repository 介面
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;
}
在使用 Jackson 時，您還可以使用@JsonManagedReferenceand@JsonBackReference來防止嵌套提取或無限遞回。
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