如何在避免复杂对象的情况下将 dto 映射到实体

Question

我尝试将 dto 映射到避免复杂对象的实体，但是当我尝试保存文章实体时出现 null 异常？ 在我的 ArticleRequest 而不是使用 Department & ArticleCategory 作为一个完整的对象我只是把他们的 ids (uid) 放在了。

这是我的文章请求：

@Slf4j
@Builder
@Data
public class ArticleRequest {

    private Long id;

    @Size(min = 32, message = "uid should have at least 32 characters")
    private String uid;

    @Size(min = 2, message = "title should have at least 2 characters")
    private String title;

    @NotBlank(message = "content should not be empty value")
    private String content;

    @NotNull(message = "article category id should not be null value")
    private String articleCategoryUid;

    @NotNull(message = "department id should not be empty value")
    private String departmentUid;

    @JsonIgnore
    private List<ArticleVote> articleVoteList;

    public static ArticleRequest fromEntity(Article article) {
        if (article == null) {
            log.warn("Class: ArticleRequest || Method: fromEntity() || Error: article is null!!!");
            return null;
        }

        return ArticleRequest.builder()
                .id(article.getId())
                .uid(article.getUid())
                .title(article.getTitle())
                .content(article.getContent())
                .articleCategoryUid(article.getArticleCategory().getUid())
                .departmentUid(article.getDepartment().getUid())
                .build();

    }

    public static Article toEntity(ArticleRequest articleRequest) {
        if (articleRequest == null) {
            log.warn("Class: ArticleRequest || Method: toEntity() || Error: articleRequest is null!!!");
            return null;
        }

        Article article = new Article();
        article.setId(articleRequest.getId());
        article.setUid(articleRequest.getUid());
        article.setTitle(articleRequest.getTitle());
        article.setContent(articleRequest.getContent());
        article.getArticleCategory().setUid(articleRequest.getArticleCategoryUid()); // i have null exeption here !! because ArticleCategory already null
         article.getDepartment().setUid(articleRequest.getDepartmentUid()); // i have null exeption here !! because Department already null
        return article;
    }
}

这是我的基础实体

@Data
@NoArgsConstructor
@AllArgsConstructor
@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
public class BaseEntity implements Serializable {

    //region Simple Properties

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false, updatable = false)
    private Long id;

    @NotNull
    @Size(min = 32, message = "uid should have at least 32 characters")
    @Column(name = "uid", nullable = true,updatable = false)
    private String uid;

    //endregion

}

这是我的文章分类类

@Data
@Entity
@Table(name = "article_categories", schema = "public")
public class ArticleCategory extends BaseEntity {

    //region Simple Properties

    @NotNull
    @Size(min = 2, message = "name should have at least 2 characters")
    @Column(name = "name")
    private String name;

    @NotNull
    @Size(min = 2, message = "slug should have at least 2 characters")
    @Column(name = "slug")
    private String slug;

    @NotNull
    @Size(min = 2, message = "description should have at least 2 characters")
    @Column(name = "description")
    private String description;

    //endregion

    //region Complex Properties
    @JsonIgnore
    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "articleCategory", orphanRemoval = true)
    private List<Article> articleList;
    //endregion}

这是我的系类

@Data
@Entity
@Table(name = "departments", schema = "public")
public class Department extends BaseEntity {

    //region Simple Properties
    @Size(min = 2,message = "name should have at least 2 characters")
    @Column(name = "name")
    private String name;

    @Enumerated(EnumType.STRING)
    @Column(name = "status")
    private DepartmentStatusEnum status;

    //endregion

    //region Complex Properties

    @JsonIgnore
    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "department", orphanRemoval = true)
    private List<Article> articleList;
}

这是我的服务

@Override
    public ArticleRequest saveArticle(ArticleRequest articleRequest) {
        if (articleRequest == null) {
            throw new InvalidEntityException(CustomErrorMessage.ARTICLE_CAN_NOT_BE_NULL.getMessage(), CustomErrorCodes.ARTICLE_NOT_VALID);
        }
        articleRequest.setUid(UUID.randomUUID().toString());
        Article saveArticle=ArticleRequest.toEntity(articleRequest);// null exception
        Article newArticle = articleRepository.save(saveArticle);
        ArticleRequest newArticleRequest = ArticleRequest.fromEntity(newArticle);
        return newArticleRequest;
    }

那么我该如何保存我的文章实体并以正确的方式传递文章类别和部门的 uid！

提前致谢。

Answer 1

给出的信息不是一个好主意，你应该在你的问题中跳过课程部门和文章

可能你的问题在这里：

article.getArticleCategory().setUid(articleRequest.getUid()); article.getDepartment().setUid(articleRequest.getUid());

你应该设置你的文章的ArticleCategory和部门，创建一个新的对象并设置它们。 我认为解决方案是将这些行替换为：

article.setArticleCategory(new ArticleCategory());
article.getArticleCategory().setUid(articleRequest.getArticleCategoryUid()); 
article.setDepartment(new Department());
article.getDepartment().setUid(articleRequest.getDepartmentUid());

---

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TransientPropertyValueException：对象引用了一个未保存的瞬态实例 - 在刷新之前保存瞬态实例

您应该在 Article 对象的持久化之前将 Properties 值保存或持久化在数据库（实例）中，因此代码将是这样的：

ArticleCategory ac = new ArticleCategory();
ac.setUid(articleRequest.getArticleCategoryUid());// if you need you can set the other properties of the ac , get them from the articleRequest
articleCategoryRepository.save(ac);
Department dep = new Department();
dep.setUid(articleRequest.getDepartmentUid());
departmentRepository.save(dep);
article.setArticleCategory(ac);
article.setDepartment(dep);
articleRepository.save(article);

Answer 2

article.getArticleCategory() //this gives you the NPE

在调用 articleCategory 的 getter 方法之前初始化它。

例如：

article.setArticleCategory(new ArticleCategory());

部门也一样。在调用getDepartment()之前初始化部门对象