无法处理托管/反向引用“defaultReference”：找不到反向引用属性

Question

我有两个模型类。一个是

@Entity(name = "userTools")
@Table(uniqueConstraints = @UniqueConstraint(columnNames = { "assignToUser_id","toolsType_id" }))
@Inheritance(strategy = InheritanceType.JOINED)
@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "className")
@JsonIgnoreProperties(ignoreUnknown = true)
public class UserTools {

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

    @OneToOne
    private ToolsType toolsType;

    @OneToMany(mappedBy = "userTools", fetch = FetchType.EAGER, cascade = { CascadeType.ALL }, orphanRemoval = true)
    @Cascade(org.hibernate.annotations.CascadeType.DELETE)
    @JsonManagedReference
    private List<UserToolsHistory> userToolsHistory;
}

第二个是

@Entity(name = "userToolsHistory")
@JsonIgnoreProperties(ignoreUnknown = true)
public class UserToolsHistory {

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

    @OneToOne
    private ToolsType toolsType;

    @ManyToOne
    @JsonIgnore
    @JsonBackReference
    private UserTools userTools; 

    private String comments;
}

但保存时出现此错误：

Can not handle managed/back reference 'defaultReference': no back
reference property found from type [collection type; class
java.util.List, contains [simple type, class
com.dw.model.tools.UserToolsHistory]]

Answer 1

为了使故障排除更容易，您可以为每个 @JsonManagedReference 和 @JsonBackReference 添加不同的名称，例如：

@JsonManagedReference(value="userToolsHistory")
    private List<UserToolsHistory> userToolsHistory;

这样错误更有意义，因为它会打印引用名称而不是“defaultReference”。

请指出您要序列化哪个实体 - UserTools 或 UserToolsHistory？无论如何，您可以尝试将 getter 和 setter 添加到您的实体中，然后将 @JsonIgnore 添加到“child”类的“get{Parent}()”中。

Answer 2

您面临的异常源于 MappingJackson2HttpMessageConverter。

要修复它，请交换注释，以便得到：

public class UserTools {
...
@JsonBackReference
private List<UserToolsHistory> userToolsHistory;
...
}

public class UserToolsHistory {
....    
@JsonManagedReference
private UserTools userTools; 
----
}

本教程解释了必须如何完成：jackson-bidirectional-relationships-and-infinite-recursion

Answer 3

@JsonManagedReference 和 @JsonBackReference 并将其替换为 @JsonIdentityInfo