我確實在項目中的三個模型對象之間有關系（文章末尾的模型和存儲庫片段）。當我調用PlaceRepository.findById它時，會觸發三個選擇查詢：（“ sql”）SELECT * FROM place p where id = argSELECT * FROM user u where u.id = place.user.idSELECT * FROM city c LEFT OUTER JOIN state s on c.woj_id = s.id where c.id = place.city.id（對我而言）這是非常不正常的行為。據閱讀Hibernate文檔后所知，它應該始終使用JOIN查詢。在類中FetchType.LAZY更改為 查詢時（帶有附加SELECT 的查詢）沒有任何區別，而在類更改為 （使用JOIN查詢時）則沒有變化。FetchType.EAGERPlaceCityFetchType.LAZYFetchType.EAGER當我使用CityRepository.findById抑制射擊時，有兩個選擇：SELECT * FROM city c where id = argSELECT * FROM state s where id = city.state.id我的目標是在所有情況下都具有sam行為（始終為JOIN或SELECT，但首選JOIN）。型號定義：地點：@Entity@Table(name = "place")public class Place extends Identified { @Fetch(FetchMode.JOIN) @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "id_user_author") private User author; @Fetch(FetchMode.JOIN) @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "area_city_id") private City city; //getters and setters}市：@Entity@Table(name = "area_city")public class City extends Identified { @Fetch(FetchMode.JOIN) @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "area_woj_id") private State state; //getters and setters}倉庫：PlaceRepositorypublic interface PlaceRepository extends JpaRepository<Place, Long>, PlaceRepositoryCustom { Place findById(int id);}UserRepository：public interface UserRepository extends JpaRepository<User, Long> { List<User> findAll(); User findById(int id);}城市資料庫：public interface CityRepository extends JpaRepository<City, Long>, CityRepositoryCustom { City findById(int id);}
3 回答
動漫人物
TA貢獻1815條經驗 獲得超10個贊
我認為Spring Data會忽略FetchMode。在使用Spring Data時，我總是使用@NamedEntityGraph和@EntityGraph批注
@Entity
@NamedEntityGraph(name = "GroupInfo.detail",
attributeNodes = @NamedAttributeNode("members"))
public class GroupInfo {
// default fetch mode is lazy.
@ManyToMany
List<GroupMember> members = new ArrayList<GroupMember>();
…
}
@Repository
public interface GroupRepository extends CrudRepository<GroupInfo, String> {
@EntityGraph(value = "GroupInfo.detail", type = EntityGraphType.LOAD)
GroupInfo getByGroupName(String name);
}
不負相思意
TA貢獻1777條經驗 獲得超10個贊
首先，@Fetch(FetchMode.JOIN)并且@ManyToOne(fetch = FetchType.LAZY)是對立的，一個指示EAGER的獲取，而另一個則指示LAZY的獲取。
急切的獲取很少是一個好的選擇，對于可預期的行為，最好使用query-time JOIN FETCH指令：
public interface PlaceRepository extends JpaRepository<Place, Long>, PlaceRepositoryCustom {
@Query(value = "SELECT p FROM Place p LEFT JOIN FETCH p.author LEFT JOIN FETCH p.city c LEFT JOIN FETCH c.state where p.id = :id")
Place findById(@Param("id") int id);
}
public interface CityRepository extends JpaRepository<City, Long>, CityRepositoryCustom {
@Query(value = "SELECT c FROM City c LEFT JOIN FETCH c.state where c.id = :id")
City findById(@Param("id") int id);
}
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