在项目中使用jpa进行多表连接查询，基本上返回的都是多张表中的数据。那么问题来了，这关联返回的数据那么多，还是不同表当中的数据，数据库中也没有表和它对应啊，怎么处理呢？返回Object吗？
其实可以用新建Vo的方法解决，话不多说，直接看代码示例：
示例实体类如下：
1.教师类
public class Teacher implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "teacher_name")
private String teacherName;
@Column(name = "teacher_id_card")
private String teacherIdCard;
@Enumerated(EnumType.STRING)
@Column(name = "sex")
private Sex sex;
@Enumerated(EnumType.STRING)
@Column(name = "teacher_status")
private TeacherStatus teacherStatus;
@Enumerated(EnumType.STRING)
@Column(name = "highest_degree")
private HighestDegree highestDegree;
@Enumerated(EnumType.STRING)
@Column(name = "specialized_technical_job")
private SpecializedTechnicalJob specializedTechnicalJob;
// getter setter 构造 tostring省略了，自己加哈........
}
2.学校类
public class School implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "school_name")
private String schoolName;
@NotNull
@Column(name = "school_principal", nullable = false)
private String schoolPrincipal;
// getter setter 构造 tostring省略了，自己加哈........
}
接收多表关联返回结集，新建Vo类：该类中放你返回的数据，需要什么放什么（我这里放的是school和teacher两张表的定义）
public class SchoolTeacherVo {
private String teacherIdCard;
private String teacherName;
private Sex sex;
private HighestDegree highestDegree;
private SpecializedTechnicalJob specializedTechnicalJob;
private TeacherStatus teacherStatus;
private String schoolName;
// getter setter 构造 tostring省略了，自己加哈........
}
接口中方法：返回你定义的Vo泛型的list就行
@Query(value = "SELECT new com.mycompany.myapp.vo.SchoolTeacherVo( b.teacherIdCard,b.teacherName,b.sex,b.highestDegree,b.specializedTechnicalJob,b.teacherStatus,c.schoolName) FROM ScheduleTeacher a inner JOIN Teacher b on a.teacher.id=b.id LEFT JOIN School c on b.school.id=c.id WHERE a.schedule.id= :scheduleId")
List<SchoolTeacherVo>getTeachers(@Param("scheduleId") Long scheduleId);
注意：写sql时@Query(value = "SELECT new com.mycompany.myapp.vo.XXXVo( a.xxx,b.xxx)FROM XXX a inner JOIN YYY b on a.id=b.xxid WHERE XXXX= :XXX")
再次强调 new 绝对不能少，后面最好跟全限定类名（不写有可能找不到这个类），还有new com.mycompany.myapp.vo.XXXVo( )括号里面写你查得东西，注意这里面返回数据顺序要和你实体类中构造方法参数顺序一致，否则会出错。
运行结果如下：