如何在Spring Boot Data Jpa应用程序中使用条件查询

Question

public interface StudentRepository extends CrudRepository<StudentEntity, Integer>{
    @Query(value = "" 
        + "SELECT s.studentname "
        + "FROM   studententity s, "
        + "       courseentity c "
        + "WHERE  s.courseid = c.courseid "
        + "       AND s.courseid IN (SELECT c.courseid "
        + "                          FROM   courseentity c "
        + "                          WHERE  c.coursename = ?1)")
    List<String> nameByCourse(String coursename);
}

Answer 1

从文档

要用自定义功能丰富存储库，首先要为自定义功能定义接口和实现。使用您提供的存储库接口来扩展自定义接口。

定义接口，如下所示

public interface StudentRepositoryCustom {

    List<String> nameByCourse(String coursename);

}

@Service
class StudentRepositoryImpl implements StudentRepositoryCustom {

    @PersistenceContext
    private EntityManager em;

    public List<String> nameByCourse(String coursename) {            
        CriteriaBuilder cb = em.getCriteriaBuilder();
        //Using criteria builder you can build your criteria queries.
    }

}

public interface StudentRepository extends CrudRepository<StudentEntity, Integer>, StudentRepositoryCustom {

}