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Question

我有两个实体，分别是文章名称和文章类别。 他们有一对多的关系。 我使用@JsonIdentityInfo(generator=ObjectIdGenerators.PropertyGenerator.class,property = "id") 但是我在spring data rest中看不到文章类别（category_id）的数据。

---

ArticleCategory.class

@Entity
@Table(name = "article_category")
@Getter
@Setter
public class ArticleCategory implements Serializable {


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


    @Column(name = "category_name")
    private String categoryName;


    @OneToMany(cascade = CascadeType.ALL, mappedBy = "articleCategory", fetch = FetchType.LAZY)
    private Set<Article> articles = new HashSet<>();


}

---

文章.class

@Entity
@Table(name = "article")
@Getter
@Setter
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "id")
public class Article implements Serializable {

    public Article() {
    }


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

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "category_id", nullable = false)
    private ArticleCategory articleCategory;


    @Column(name = "title")
    private String title;

    @Column(name = "image_url")
    private String image_url;

    @Column(name = "short_description")
    private String short_description;

    @Column(name = "text")
    private String text;

    @Column(name = "keywords", nullable = true)
    private String keywords;

    @Column(name = "visit", nullable = false)
    private int visit;

    @Column(name = "code", nullable = false)
    private UUID code;

    @Column(name = "date_created")
    @CreationTimestamp
    private Date dateCreated;

    @Column(name = "date_updated", nullable = false)
    @UpdateTimestamp
    private Date dateUpdated;


    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;


    public Article(String title, String image_url, String short_description, String text, String keywords, int visit, UUID code) {
        this.title = title;
        this.image_url = image_url;
        this.short_description = short_description;
        this.text = text;
        this.keywords = keywords;
        this.visit = visit;
        this.code = code;
    }
}

---

文章存储库

@CrossOrigin("http://localhost:4200")
@RepositoryRestResource(collectionResourceRel = "article", path = "article")

public interface ArticleRepository extends JpaRepository<Article,Long> {

    Article findByCode(UUID uuid);


}

---

这是spring data rest的输出

enter image description here

Answer 1

这正是因为您使用了@JsonManagedReference 和@JsonBackReference。使用时请注意以下几点：

• @JsonManagedReference 是关系的前向部分，是正常序列化的部分。
• @JsonBackReference 是关系的后面部分，序列化时会省略。
• 序列化的Article 对象不包含对ArticleCategory 对象的引用。

---

如果您想在序列化Article 时拥有任何ArticleCategory 数据，您可以使用@JsonIdentityInfo 以便序列化其中一个属性（在这种情况下，我为两者选择了id）：

@Entity
@Table(name = "article")
@Getter
@Setter
@JsonIdentityInfo(
  generator = ObjectIdGenerators.PropertyGenerator.class, 
  property = "id")
public class Article implements Serializable{ 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "category_id", nullable = false)
    private ArticleCategory articleCategory;
}

@Entity
@Table(name = "article_category")
@Getter
@Setter
@JsonIdentityInfo(
  generator = ObjectIdGenerators.PropertyGenerator.class, 
  property = "id")
public class ArticleCategory implements Serializable {

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

    @Column(name = "category_name")
    private String categoryName;

    @OneToMany(cascade = CascadeType.ALL,mappedBy = "articleCategory" ,fetch = FetchType.LAZY)
    private Set<Article> articles=new HashSet<>();
}

---

如果您只对categoryId 感兴趣，另一种可能性是在private Set<Article> articles 属性上使用@JsonIgnore，这样它就不会被序列化：

@Entity
@Table(name = "article_category")
@Getter
@Setter
public class ArticleCategory implements Serializable {

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

    @Column(name = "category_name")
    private String categoryName;

    @JsonIgnore
    @OneToMany(cascade = CascadeType.ALL,mappedBy = "articleCategory" ,fetch = FetchType.LAZY)
    private Set<Article> articles=new HashSet<>();
}

---

如果这些都不适合您的需求，您可能需要实现自己的自定义序列化程序。您可以在https://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion 阅读有关所有这些选项的更多信息。

Answer 2

我使用控制器解决了问题 这就是 @JsonManageRefrence 和 @JsonBackRefrence 不起作用的原因

我用两个实体中的急切加载替换了延迟加载

@ManyToOne(fetch = FetchType.Eager)
@JoinColumn(name = "user_id")
@JsonManageRefrence
private User user;



 @OneToMany(cascade = CascadeType.ALL, mappedBy = "articleCategory", 
 fetch = FetchType.Eager)
    @JsonBackRefrence
    private Set<Article> articles = new HashSet<>();

然后添加一个控制器

package com.example.demo;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/getAllArticle")
public class MyController {

    private ArticleRepository articleRepository;

    // you must do constructor injection

@GetMapping("/getAllArticle")
public List<Article> allArticle()
{
    return  articleRepository.findAll();
}

}