Spring Boot 中的 Json 反序列化器 - 如何进行反序列化和自关系

Question

我正在从事一个 Spring Boot 项目，需要将 JSON 转换为实体以保存在 postgresql 数据库中。我有一些自引用关系，不知道如何反序列化并保存在数据库中。我有一个与其他用户有某种关系的用户。例如，用户 A 是用户 B 的客户。

让我们看示例代码以更好地理解...

我有以下 JSON 将信息保存到数据库中

{
  id: 1,
  name: "myName"
  relations:[
     {
       "user_id": "2",
       "relation": "relation_name"
     },
     {
       "user_id": "3",
       "relation": "other_relation_name"
     }
  ]
}

我有以下课程（示例代码）

@Entity
@Data
public class User {
    @Id
    private Long id;
    private String name;
    @OneToMany(mappedBy = "user_id_parent")
    private List<UserRelation> relations;
}

@Entity
@Data
public class UserRelation {
    @Id
    @ManyToOne(targetEntity = User.class)
    @JoinColumn(name = "user_id_parent", referencedColumnName = "id", nullable = false)
    private Long user_id_parent;
    @Id
    @JsonProperty("user_id")
    private Long user_id_child;
    private String relation;
}

为了反序列化并保存在数据库中，我这样做

ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json.toString(), User.class);

// user have [User(id=1, name:"myName", relations=[UserRelation(user_id_child=2, relation="relation_name", user_id_parent=null)]]

userRepository.save(user);

但是，我有这个错误：

Unable to find com.compani.project.domain.UserRelation with id UserRelation(user_id_child=2, relation=null, user_id_parent=null)

我不知道如何做好这项任务。有什么想法或建议吗？

编辑 @Wladimir Diskowski建议在User实体中定义Cascade Persist，我这样写

@Entity
@Data
public class User {
    @Id
    private Long id;
    private String name;
    @OneToMany(mappedBy = "user_id_parent", cascade = { CascadeType.PERSIST })
    private List<UserRelation> relations;
}

但是我有这个错误

not-null property references a null or transient value : com.compani.project.domain.UserRelation.user_id_parent

我认为问题在于，为什么要在

user_id_parent

中设置paren用户的ID（在本例中为值1）

Answer 1

我的意思是：

@Entity
@Data
public class User {
    @Id
    private Long id;
    private String name;
    @OneToMany(mappedBy = "userParent", cascade = { CascadeType.PERSIST })
    private List<UserRelation> relations;
}

@Entity
@Data
public class UserRelation {
    @Id
    @ManyToOne(targetEntity = User.class)
    @JoinColumn(name = "user_id_parent", referencedColumnName = "id", nullable = false)
    @JsonIgnore
    private User userParent;
    @Id
    @JsonProperty("user_id")
    private Long user_id_child;
    private String relation;
} 

ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json.toString(), User.class);
user.relations.foreach(r -> r.setUserParent(user));
userRepository.save(user);