JPQL 外键查询

Question

There are two tables PersonEntity and cityentity. PersonEntity in the database is linked to cityentity by the external key fk_cityid. I need to select all the records (names) of the PersonEntity table with the given CityId. Join is used everywhere for this, but in this case I don't need data from the cityentity table, only the name field of the PersonEntity table. Here is a description of the classes:

@Entity
public class PersonEntity {
    private Long id;
    private String name;
    private CityEntity cityId;
}
@Entity
public class CityEntity {
    private Long id;
    private String name;
}

Here is the HQL query:

@Repository
public interface PersonEntityRepository extends JpaRepository<PersonEntity, Long> {
  @Query("select p.name FROM PersonEntity p where (p.name = :name or :name is null) " +
        "and (p.cityId = :cityId or :cityId is null)")
    List<PersonEntity> findByNameAndCity (
        @Param("name") String name,
        @Param("cityId") CityEntity cityId);
}

tried by id:

@Query("select p.name FROM PersonEntity p where (p.name = :name or :name is null) " +
        "and (p.cityId.id = :cityId or :cityId is null)")
    List<PersonEntity> findByNameAndCity (
        @Param("name") String name,
        @Param("cityId") Long cityId);

In both cases, the error is: "the data type could not be determined".

options for calling the function:

servisPerson.findByNameAndCity (null, cityId);

or

servisPerson.findByNameAndCity (name, null);

In fact, there are more than two parameters. I only show two for simplification.

servisPerson.findByNameAndCity (name, age, ..., cityId);

Answer 1

Person entity should look something like this

@Entity
public class PersonEntity {
     private Long id;
     private String name;

     @OneToOne
     @JoinColumn(name = "city_id")
     private CityEntity city;
}

Than you can write your query like this

List<PersonEntity> findByNameAndCityOrNameIsNullOrCityIsNull(String name, CityEntity city);

Spring Data JPA is so smart to generate the query for you under the hood.

BTW, you attempted to write JPQL , not HQL .

EDIT (reaction on comment about long method names):

I would suggest to avoid creating JPQL query, because is is more error prone. If you don't like lengthy method name, you can wrap it into shorter default method within repository:

@Repository
public interface PersonEntityRepository extends  JpaRepository<PersonEntity, Long> {
     List<PersonEntity> findByNameAndCityOrNameIsNullOrCityIsNull(String name, CityEntity city);
     
     default List<PersonEntity> shortName(String name, CityEntity city) {
         return findByNameAndCityOrNameIsNullOrCityIsNull(name, city);
     }
}