@ManyToMany 与 EclipseLink 2.5.2 和 Jackson 2.4.4

Question

在尝试更新实体时，我触发了一个 REST 请求：PUT <ip>/categories/5，其 JSON 正文：{"id":"4","name":"otherCategory","contentList":[]}

错误信息是：

WARN  [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] 
(default task-27) Failed to evaluate deserialization for type [simple type, class 
com.example.domain.assetmanagement.Category]: java.lang.IllegalArgumentException: 
Can not handle managed/back reference 'users-roles': no back reference property 
found from type [collection type; class java.util.List, contains [simple type, 
class com.example.domain.user.permission.Role]]

Category.java不包含这个关系，它只有id、name、contentList三个属性

@Id
@GeneratedValue(generator = "UUID_CATEGORY")
private String id;

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

@OneToMany(mappedBy = "category")
@JsonManagedReference("category-content")
private List<Content> contentList;

[+getters/setters]

关系在 User 和 Role 中定义，如下所述：http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Relationship_Mappings/Collection_Mappings/ManyToMany

用户.java：

@ManyToMany
@JoinTable(name = "user_role",
        joinColumns = {
                @JoinColumn(
                        name = "user_id",
                        referencedColumnName = "id"
                )
        },
        inverseJoinColumns =
        @JoinColumn(
                name = "role_id",
                referencedColumnName = "id"
        )
)
@JsonManagedReference("users-roles")
private List<Role> roles;

角色.java：

@ManyToMany(mappedBy = "roles")
private List<User> users;

当我将@JsonBackReference 添加到 Role.java 中的 users 属性时，我收到以下错误：

WARN  [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] 
(default task-28) Failed to evaluate deserialization for type [simple type, class
com.example.domain.assetmanagement.Category]: java.lang.IllegalArgumentException: 
Can not handle managed/back reference 'users-roles': back reference type 
(java.util.List) not compatible with managed type (com.example.domain.user.User)

Answer 1

根据http://jackson-users.ning.com/forum/topics/deserializing-objects-with-bi-directional-many-to-many-relations，您需要在两个实体上使用@JsonIdentityInfo，而不是在映射上使用@JsonManagedReference 和@JsonBackReference。