java - 将 jpa (Hibernate) 中的 native (连接)查询转换为 json

Question

我正在开发一个 Spring Boot 项目，并使用 jpa 进行数据持久化。现在我有两个相互关联的表:用户和项目。一名用户可以拥有任意数量的元素，而一件元素只能由一个用户拥有。
这是我的 pojo:
用户

@Entity
@Table(name="users", uniqueConstraints = {
            @UniqueConstraint(columnNames = {
                "email"
            })
    })
@EntityListeners(AuditingEntityListener.class)
@JsonIgnoreProperties(value = {"createdAt", "updatedAt"}, allowGetters = true)
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank
    @NaturalId
    @Column(unique = true)
    private String email;

    @NotBlank
    @JsonIgnore
    private String password;

    @NotBlank
    private String first_name;

    @NotBlank
    private String last_name;

    @OneToMany(cascade = CascadeType.REMOVE, orphanRemoval = true)
    @JsonIgnore
    private Set<Item> items;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "user_roles",
            joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "role_id"))
    private Set<Role> roles = new HashSet<>();


    @Column(nullable = false, updatable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @CreatedDate
    private Date createdAt;

    @Column(nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @LastModifiedDate
    private Date updatedAt;

项目

@Entity
@Table(name="items")
@EntityListeners(AuditingEntityListener.class)
@JsonIgnoreProperties(value = {"createdAt", "updatedAt"}, allowGetters = true)
public class Item {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank
    @NotNull
    private String name;

    private String description;

    @NotNull 
    private Date purchase_date;

    private double price;

    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    @JoinColumn(name = "owner", nullable = true)
    private User owner;

    @Column(nullable = false, updatable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @CreatedDate
    private Date createdAt;

    @Column(nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @LastModifiedDate
    private Date updatedAt;

现在我想获取所有项目作为 RESTfull JSON。我需要将用户与项目连接起来，以便可以获得以下 JSON:

{
    "item_id":1,
    "name":"item1",
    "price":120.00,

    etc .....

    "owner_id":1,
    "owner_name":"Jon"
    etc ....

}

所以我使用自定义 native 查询

SELECT i.id, i.name, i.description ...... u.id, u.name ..... from items i , users u where i.owner = u.id

然后我返回 query.getResultList() 但是这会返回字符串数组，而不是像这样的 json

[

    [ 1 , "item1" , 120.00 , ..... , 1 , "Jon" , ....]
    [ 2 , "item2" , 420.00 ....   ]
etc...
]

如何将返回的对象直接转换为 JSON，或者转换为将列名称映射到值的映射列表，然后将其转换为 JSON？

Answer 1

您可以使用它，不需要每个请求都创建新的 DTO。

@SuppressWarnings("unchecked")
public static List<ObjectNode> getQueryResult(EntityManager entityManager, String nativeQuery, Object... parameters) {

    Query localQuery = entityManager.createNativeQuery(nativeQuery,Tuple.class);

    for(int i = 0; i < parameters.length; i++)
        localQuery.setParameter(i+1, parameters[i]);

    return toJson(localQuery.getResultList());
}

private static List<ObjectNode> toJson(List<Tuple> results) {

    List<ObjectNode> json = new ArrayList<>();

    ObjectMapper mapper = new ObjectMapper();

    for (Tuple tuple : results)
    {
        List<TupleElement<?>> cols = tuple.getElements();

        ObjectNode node = mapper.createObjectNode();

        for (TupleElement col : cols)
            node.put(col.getAlias(), tuple.get(col.getAlias()).toString());

        json.add(node);
    }
    return json;
}