java - Spring Boot - 使用自定义对象数组 JSON 序列化自定义对象

Question

有这样一个类:

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private int key;
private String text;
private Tag[] tags;
private String title;
private boolean valid;
public Activity(int key, String text, Tag[] tags, String title) {
    this.key = key;
    this.text = text;
    this.tags = tags;
    this.title = title;
    valid = true;
}

它有一个与之关联的Tag数组。标签如下所示:

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private long activityId;
private String keyword;

public Tag(String keyword){
    this.keyword = keyword;
    activityId = -1;
}

Activity 和 Tag 都是实体，并且都有存储库:

public interface TagRepository extends CrudRepository<Tag, Long> {

}

public interface ActivityRepository extends CrudRepository<Activity, Long> {

}

有一个创建方法，它在数据库中存储 Activity 对象:

  @PostMapping
  public Activity create(@RequestBody Activity input) {
      if(input.getTags() != null) {
          for(Tag t : input.getTags()) {
              t.setActivityId(input.getId()); //associate which activity has which tags
              tagRepository.save(t);
          }
      }

      return activityRepository.save(input);
  }

我通过 POST 传输此 JSON:

{
    "key":2,
    "text":"Hello",
    "tags":[{
        "keyword":"h"
    },{
        "keyword":"b"
    }
    ],
    "title":"world"
}

但我收到此错误:

"status": 500,
"error": "Internal Server Error",
"exception": "org.springframework.orm.jpa.JpaSystemException",
"message": "could not serialize; nested exception is org.hibernate.type.SerializationException: could not serialize"

这两个类都有每个成员变量的 getter/setter，并且都有默认构造函数，我只是没有在此处显示它们，以使问题尽可能简短。

Answer 1

首先，您需要在 Activity 和标签之间创建关系。 Activity 有很多标签，那么关系应该是 oneToMany。

http://www.baeldung.com/hibernate-one-to-many

@Entity
@Table(name="ACTIVITY")
public class Activity {
  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  private long id;
  private int key;
  private String text;

  @OneToMany(mappedBy="activity")
  private List<Tag> tags;

  private String title;
  private boolean valid;
  public Activity(int key, String text, List<Tag> tags, String title) {
    this.key = key;
    this.text = text;
    this.tags = tags;
    this.title = title;
    valid = true;
  }
}

@Entity
@Table(name="TAG")
public class Tag {
  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  private long id;

  @ManyToOne
  @JoinColumn(name="activity_id", nullable=false)
  private Activity activity;

  private String keyword;

  public Tag(String keyword){
    this.keyword = keyword;
    activityId = -1;
  }
}

首先，您没有使用属性CASCADE.ALL，这意味着您将手动处理标签实体的保存。

@PostMapping
  public Activity create(@RequestBody Activity input) {
      if(input.getTags() != null) {
          //you are saving all the nested tags manually before saving the activity
          for(Tag t : input.getTags()) {
              tagRepository.save(t);
          }
      }
      //now you are saving activity which contains these tags
      return activityRepository.save(input);
  }