我正在开发一个Spring Boot项目,并且正在使用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。一个用户可以拥有任意数量的项目,而一个项目只能由一个用户拥有。
这是我的pojos:
用户数

@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;


物品

@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,我想以RESTfull JSON形式获取所有项目。我需要为用户添加项目,以便获得以下JSON:

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

    etc .....

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

}


所以我正在使用自定义的本机查询

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(),但是返回的是字符串数组,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或映射到将列名映射到值的映射列表,然后将其转换为JSON?

最佳答案

您可以使用构造函数表达式创建一个包含所需数据的DTO(数据传输对象)。

package dto;

public class ItemDTO {

   private final Long item_id;
   private final String name;
   private final Long owner_id;
   private final String owner_name;

   public ItemDTO(Long item_id, String name, Long owner_id, String owner_name) {
      // set the fields
   }

   // getters
}


然后在构造函数表达式查询中使用此DTO(重要说明:这仅适用于JPQL查询而不适用于本机查询)

SELECT new dto.ItemDTO(i.id, i.name, i.owner.id, i.owner.name) from Item i where i.owner.id = u.id


此DTO可用于序列化为JSON。

在此处阅读有关构造函数表达式的更多信息:
https://vladmihalcea.com/the-best-way-to-map-a-projection-query-to-a-dto-with-jpa-and-hibernate/

关于java - 将JPA(Hibernate)中的 native (联接)查询转换为JSON,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/51854878/

10-16 13:22
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