2023年12月8日 问题： 使用 Spring Data JPA 定义 Repo find方法时，发现会执行了N+2条SQL 。 Entity 定义如： @Data @Entity @Table(name = "event") public class Event implements Serializable { .... @OneToOne(mappedBy = "event") private Action action; } @Data @Entity @Table(name = "action") public class Action implements Serializable { .... @JsonIgnore @OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "event_id", insertable = false, updatable = false) private Event event; } 12345678910111213141516171819202122232425 @Data@Entity@Table(name = "event")public class Event implements Serializable {.... @OneToOne(mappedBy = "event") private Action action; } @Data@Entity@Table(name = "action")public class Action implements Serializable {.... @JsonIgnore @OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "event_id", insertable = false, updatable = false) private Event event; } 解决： 使用 @Query 及 left fetch join 来减少 SQL，最后只会执行两条 sql 如： @RepositoryRestResource(path = "event") public interface EventRestRepo extends PagingAndSortingRepository<Event, Integer>, CrudRepository<Event, Integer> { @Query("select e" + " from Event e " + " left join fetch e.action " + " where e.companyCode=?1 ") Page<Event> find2(String companyCode, Pageable p); } 12345678 @RepositoryRestResource(path = "event")public interface EventRestRepo extends PagingAndSortingRepository<Event, Integer>, CrudRepository<Event, Integer> { @Query("select e" + " from Event e " + " left join fetch e.action " + " where e.companyCode=?1 ") Page<Event> find2(String companyCode, Pageable p);} 参考：