如何使用 JPQL 从 Spring 数据存储库获取 HashMap 结果？

Question

I've currently implemented a Ternary relationship using Map between User , Shop and Role . So in my User Entity i have this mapping:

User.java

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

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(nullable = false)
private int id;

@Basic(fetch = FetchType.LAZY, optional = false)
private String uuid;

@NotBlank(message = "First name can not be empty")
@Column(name = "usFname")
private String usFname;

@NotBlank(message = "Username can not be left empty")
@Column(name = "us_lname")
private String usLname;

@NotBlank(message = "Email field can not be empty")
@ValidEmail
    @Column(name = "usEmail", unique = true)
    @Basic(fetch = FetchType.LAZY, optional = false)
    private String usEmail;
 //this is the actual mapping
//a user can have a list of shops, but one role assigned for each shop
@ManyToMany
    @MapKeyJoinColumn(name = "shop_fk")
    @JoinTable(name = "user_shop_role",
            joinColumns = @JoinColumn(name = "user_fk"), inverseJoinColumns = @JoinColumn(name = "role_fk"))
    private Map<Shop, Role> shopRoleMap = new HashMap<>();
//GETTERS AND SETTERS,
}

Role.java

@Entity
@Table(name = "ro_roles")
public class Role {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(nullable = false)
private int id;

@Column(name = "rn_role_name")
private String roleName;

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getRoleName() {
    return roleName;
}

public void setRoleName(String roleName) {
    this.roleName = roleName;
}

}

Shop.java

@Entity
@Table(name = "sh_shops")
public class Shop {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(nullable = false)
private int id;

@NotBlank(message = "Shop name can not be left blank")
private String sh_name;

@NotBlank(message = "please provide shop icon")
private String sh_icon;

@NotBlank(message = "please fill the shop description")
private String sh_description;

@NotBlank
private String sh_tag;
//setters, getters, equals, hashCode methods.
}

This mapping gives me another table ( user_shop_role ) in the database that has user_fk , shop_fk and role_fk which is lovely. The difficult bit is to make a Query using Spring Data JPA and get the result as a HashMap for a given user as this: HashMap<Shop,Role> for the logged in user.

At the UserRepository layer i have tried this:

interface UserRepository extends JpaRepository and i have this query...

@Query("SELECT u FROM User u join shopRoleMap m where key(m)= usEmail")
     public HashMap<Shop, Role> findByUser(String email);


}

How can i get results for a ternary relationship mapped using a Map Collection to get a list of shops and corresponding role value. More of a key,value result?

Answer 1

• Repository method.

    @Repository
    public interface UserRepository
            extends JpaRepository<User, Integer> {
    
        @Query("SELECT key(m), value(m) FROM User u join u.shopRoleMap m" +
                " where u.usEmail = :email")
        List<Object[]> findByUserEmail(String email);
    
    }

• Generated query.

    select
        shop3_.id as id1_1_0_,
        role2_.id as id1_0_1_,
        shop3_.sh_description as sh_descr2_1_0_,
        shop3_.sh_icon as sh_icon3_1_0_,
        shop3_.sh_name as sh_name4_1_0_,
        shop3_.sh_tag as sh_tag5_1_0_,
        role2_.rn_role_name as rn_role_2_0_1_ 
    from
        us_users user0_ 
    inner join
        user_shop_role shoprolema1_ 
            on user0_.id=shoprolema1_.user_fk 
    inner join
        ro_roles role2_ 
            on shoprolema1_.role_fk=role2_.id 
    inner join
        sh_shops shop3_ 
            on shoprolema1_.shop_fk=shop3_.id 
    where
        user0_.us_email=?

Update with above code plus another way

Github repo - https://github.com/kavi-kanap/stackoverflow-6313585

Answer 2

Spring Data JPA has a feature called Property Expressions where you can access the child or related entity

For example

List<Shop> findByUser_email(String email);

For more details refer to this

Spring Data JPA doc

Sample example