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;
}

但是在保存时我收到了这个错误：

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

您遇到的异常源于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 2

为了简化问题排查，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，因为它打印引用名称而不是'defaultReference'。

请指出您尝试序列化的内容 - UserTools或UserToolsHistory？无论如何，您可以尝试将getter和setter添加到您的实体，然后将@JsonIgnore添加到“child”类中的“get {Parent}（）”。

Answer 3

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

无法处理托管/后向引用'defaultReference'：找不到后引用属性

3 个答案: