Spring Data Rest:检测到具有相同关系类型的多个关联链接

Question

关于这个问题,我检查了Spring Data Rest Ambiguous Association Exception但是无法让它为我工作.

正如您在下面的代码中看到的,我添加了@RestResource与rel其他值相等的注释.

与上面的问题类似,POST请求有效,但GET请求会抛出具有相同关系类型的多个关联链接的异常:

"无法编写JSON:检测到具有相同关系类型的多个关联链接!消除关联@ org.springframework.data.rest.core.annotation.RestResource(rel = createdBy,exported = true,path =,description =@org.springframework. data.rest.core.annotation.Description(value =))@ javax.persistence.ManyToOne(optional = true,targetEntity = void,cascade = [],fetch = EAGER)@ javax.persistence.JoinColumn(referencedColumnName = ASSIGNABLE_ID,nullable = false,unique = false,name = CREATED_BY,updatable = true,columnDefinition =,foreignKey = @ javax.persistence.ForeignKey(name =,value = CONSTRAINT,foreignKeyDefinition =),table =,insertable = true)private com.ag. persistence.domain.PersonEntity com.ag.persistence.domain.TeamEntity.createdBy使用@RestResource!(通过引用链:org.springframework.hateoas.PagedResources [\"_ embedded \"] - > java.util.UnmodifiableMap [\"people \"] - > java.util.ArrayList [0]);嵌套异常是com.fasterxml.jackson.databind.JsonMappingException:检测到多个关联 具有相同关系类型的链接!消除关联@ org.springframework.data.rest.core.annotation.RestResource(rel = createdBy,exported = true,path =,description = @ org.springframework.data.rest.core.annotation.Description(value =))@ javax.persistence.ManyToOne(optional = true,targetEntity = void,cascade = [],fetch = EAGER)@ javax.persistence.JoinColumn(referencedColumnName = ASSIGNABLE_ID,nullable = false,unique = false,name = CREATED_BY,updatable = true, columnDefinition =,foreignKey = @ javax.persistence.ForeignKey(name =,value = CONSTRAINT,foreignKeyDefinition =),table =,insertable = true)private com.ag.persistence.domain.PersonEntity com.ag.persistence.domain.TeamEntity. createdBy使用@RestResource!(通过参考链:org.springframework.hateoas.PagedResources [\"_ embedded \"] - > java.util.UnmodifiableMap [\"persons \"] - > java.util.ArrayList [0])"

这个错误似乎发生在这个类中:

@Entity
@Table(name = "team")
public class TeamEntity extends AssignableEntity {
    private String name;
    private LocalDateTime createdDate;
    private LocalDateTime modifiedDate;
    private Collection<MembershipEntity> memberships;
    private PersonEntity createdBy;
    private PersonEntity modifiedBy;

    @Basic
    @Column(name = "NAME")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Basic
    @Column(name = "CREATED_DATE")
    public LocalDateTime getCreatedDate() {
        return createdDate;
    }

    public void setCreatedDate(LocalDateTime createdDate) {
        this.createdDate = createdDate;
    }

    @Basic
    @Column(name = "MODIFIED_DATE")
    public LocalDateTime getModifiedDate() {
        return modifiedDate;
    }

    public void setModifiedDate(LocalDateTime modifiedDate) {
        this.modifiedDate = modifiedDate;
    }

    @OneToMany(mappedBy = "team")
    public Collection<MembershipEntity> getMemberships() {
        return memberships;
    }

    public void setMemberships(Collection<MembershipEntity> memberships) {
        this.memberships = memberships;
    }

    @RestResource(rel = "team_createdBy")
    @ManyToOne
    @JoinColumn(name = "CREATED_BY", referencedColumnName = "ASSIGNABLE_ID", nullable = false)
    public PersonEntity getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(PersonEntity createdBy) {
        this.createdBy = createdBy;
    }

    @RestResource(rel = "team_modifiedBy")
    @ManyToOne
    @JoinColumn(name = "MODIFIED_BY", referencedColumnName = "ASSIGNABLE_ID", nullable = false)
    public PersonEntity getModifiedBy() {
        return modifiedBy;
    }

    public void setModifiedBy(PersonEntity modifiedBy) {
        this.modifiedBy = modifiedBy;
    }
}

具有讽刺意味的是,我没有访问此特定资源.我还有其他资源createdBy和modifiedBy- 是导致这个问题的那个？

Answer 1

我怀疑你可能有exported = false你的PersonEntity对象。因此，任何引用都PersonEntity将添加到_links您的TeamEntity. 因为两个PersonEntity对象都有一个createdBy引用，所以它们与该引用发生碰撞TeamEntity.createdBy。

要了解正在发生的情况，此示例可能会有所帮助：

class Answer {
   Question q; //JPA ManyToOne back-reference
}

class Question {
   List<Answer> as; // JPA OneToMany reference
}

class UserAnswer {
   Answer a;
   Question q;
}

就我而言，因为 anAnswer只能存在于 a 中Question，所以我们在 , 上有以下内容AnswerResource，以防止导出答案：

@RestResource(exported = false)

这会导致Answer对象在父对象中序列化，而不是作为该_links部分中的引用，这最终成为问题的原因......

序列化后UserAnswer，它会呈现如下内容：

{
  "answer" : {
    "creationDate" : "2014-09-18T17:28:31.000+0000",
    "modificationDate" : "2014-09-18T17:28:31.000+0000",
    "answerText" : "Vendas",
  },
  "_links" : {
    "self" : {
      "href" : "http://localhost:9090/data/userAnswers/15"
    },
    "question" : {
      "href" : "http://localhost:9090/data/userAnswers/15/question"
    }
  }
}

请注意，上面的“_links.question”来自Answer！

因此，如果您将 a 添加Question到UserAnswer，您将看到您所询问的错误，因为它UserAnswer本身也希望包含对 a 的 _link 引用Question。

就你而言，我认为你PersonEntity和你TeamEntity都有createdBy参考资料。

我还不是 100% 确定解决方案是什么，我不知道您是否可以指定分层rel名称。