如何使用Join定义JPA存储库查询

Question

我想使用带有注释@Query的Jpa存储库进行Join查询.

我有两张桌子:

 table user 
 with iduser,user_name 

和:

 table area 
 with idarea, area_name and iduser

本机查询是:

 SELECT
 u.user_name 
 FROM
  user as u 
  INNER JOIN area as a ON a.iduser = u.iduser
  WHERE
  a.idarea = 4

现在我有一个表Hibernate实体用户和区域

所以我尝试使用UserRespository

@Query(SELECT  u.userName FROM  User u 
  INNER JOIN Area a ON a.idUser = u.idUser
  WHERE
  a.idArea = :idArea)
List<User> findByIdarea(@Param("idArea") Long idArea);

日志说:

意外的标记:

请问有什么想法吗？

我的表实体

#User Table
@Entity
@Table(name="user")
public class User implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long idUser;
    private String userName;

    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="iduser")
    public Long getIdUser() {
        return idUser;
    }

    public void setIdUser(Long idUser) {
        this.idUser = idUser;
    }

    @Column(name="user_name")
    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }
}

#AREA table

@Entity
@Table(name="area")
public class Area  implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long idArea;
    private String areaName;
    private Long idUser;

    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="idarea")
    public Long getIdArea() {
        return idArea;
    }

    public void setIdArea(Long idArea) {
        this.idArea = idArea;
    }

    @Column(name="area_name")
    public String getAreaName() {
        return areaName;
    }

    public void setAreaName(String areaName) {
        this.areaName = areaName;
    }

    @Column(name="iduser")
    public Long getIdUser() {
        return idUser;
    }

    public void setIdUser(Long idUser) {
        this.idUser = idUser;
    }       
}

Answer 1

您遇到此问题有两个原因.

• JPQL查询无效.
• 您尚未在基础JPQL查询可以使用的实体之间创建关联.

在JPQL中执行连接时,必须确保存在尝试连接的实体之间的基础关联.在您的示例中,您缺少User和Area实体之间的关联.为了创建这种关联,我们必须在User类中添加一个Area字段并建立适当的JPA Mapping.我在下面附上了User的来源.(请注意我将映射移到了字段中)

User.java

@Entity
@Table(name="user")
public class User {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="iduser")
    private Long idUser;

    @Column(name="user_name")
    private String userName;

    @OneToOne()
    @JoinColumn(name="idarea")
    private Area area;

    public Long getIdUser() {
        return idUser;
    }

    public void setIdUser(Long idUser) {
        this.idUser = idUser;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public Area getArea() {
        return area;
    }

    public void setArea(Area area) {
        this.area = area;
    }
}

建立此关系后,您可以在@Query声明中引用area对象.@Query注释中指定的查询必须遵循正确的语法,这意味着您应该省略on子句.请参阅以下内容:

@Query("select u.userName from User u inner join u.area ar where ar.idArea = :idArea")

在查看您的问题时,我还将用户和区域实体之间的关系设置为双向.以下是Area实体建立双向关系的来源.

Area.java

@Entity
@Table(name = "area")
public class Area {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="idarea")
    private Long idArea;

    @Column(name="area_name")
    private String areaName;

    @OneToOne(fetch=FetchType.LAZY, mappedBy="area")
    private User user;

    public Long getIdArea() {
        return idArea;
    }

    public void setIdArea(Long idArea) {
        this.idArea = idArea;
    }

    public String getAreaName() {
        return areaName;
    }

    public void setAreaName(String areaName) {
        this.areaName = areaName;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }
}