杰克逊双向关系(一对多)不起作用 [英] Jackson bidirectional relationship (One-to-many) not working

问题描述

在此Web服务项目中，我正在使用Spring(xml + annotations)和Hibernate(annotations).数据库关系图，模型，预期和实际输出如下所示，

I'm using Spring(xml+annotations), Hibernate(annotations) in this web service project. The database relationship diagram, models, expected and actual output are given below,

数据库表关系

Customer.java

Customer.java

@Entity
@Table(name="customer")
public class Customer implements Serializable{
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="customer_id", unique=true, nullable =false)
    long customerId;
    @Column(name="name")
    String name;
    @Column(name="secondary_name")
    String secondaryName;
    @Column(name="date")
    Date date;
    @Column(name="address")
    String address;
    @Column(name="post")
    String post;
    @Column(name="pin")
    String pin;
    @Column(name="phone")
    String phone;
    @OneToMany(fetch=FetchType.LAZY, mappedBy="customer", cascade=CascadeType.ALL)
    @JsonManagedReference
    Set<Loan> loans = new HashSet<Loan>();
    //constructors, getters and setters
}

Loan.java

Loan.java

public class Loan implements Serializable{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="loan_id", nullable=false, unique=true)
    long loanId;
    @ManyToOne(fetch = FetchType.EAGER, cascade=CascadeType.ALL)
    @JoinColumn(name="customer_id", nullable = false)
    @JsonBackReference
    Customer customer;
    @Column(name="date", nullable=false)
    Date date;
    @Column(name="amount", nullable=false)
    double amount;
    @OneToMany(fetch=FetchType.LAZY, mappedBy="loan", cascade=CascadeType.ALL)
    @JsonManagedReference
    List<Item> items = new ArrayList<Item>();
    //constructors, getters, setters
}

Item.java

Item.java

public class Item implements Serializable{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="item_id", nullable=false, unique=true)
    long itemId;
    @ManyToOne(fetch=FetchType.LAZY, cascade=CascadeType.ALL)
    @JoinColumn(name="loan_id", nullable = false)
    @JsonBackReference
    Loan loan;
    @Column(name="name", nullable=false)
    String name;
    @Column(name="weight", nullable=false)
    double weight;
    //constructors, setters, getters
}

实际输出:此处未显示客户详细信息

Actual output:Here, customer details are not shown

{  
   "loanId":4,
   "date":1484937000000,
   "amount":10000.0,
   "items":[  
      {  
         "itemId":3,
         "name":"Item1",
         "weight":10.0
      },
      {  
         "itemId":4,
         "name":"Item2",
         "weight":20.0
      }
   ]
}

预期输出:寻找贷款时也需要显示客户详细信息

Expected output: need to display customer details also when looking for a loan

{  
   "loanId":4,
   "customer":{  
      "customerId":2,
      "name":"Prem",
      "address":"Street,State"
   },
   "date":1484937000000,
   "amount":10000.0,
   "items":[  
      {  
         "itemId":3,
         "name":"Item1",
         "weight":10.0
      },
      {  
         "itemId":4,
         "name":"Item2",
         "weight":20.0
      }
   ]
}

我可以从数据库中获取客户详细信息，而无法使用Jackson Json加载它. 如果删除@JsonManagedReference，则会导致循环循环. 如果删除@JsonBackReference，则输出中没有任何影响. 完整代码位于: https://github.com/liwevire/TM_Service 预先感谢.

I can able to fetch the customer details from the database and fail to load it using Jackson Json. If I remove @JsonManagedReference, I end up with circular loop. If I remove @JsonBackReference, no effects in the output. Complete code at: https://github.com/liwevire/TM_Service Thanks in advance.

推荐答案

由于在Loan实体的Customer属性上使用了@JsonBackReference，因此Customer对象将不包括在序列化中.将@JsonManagedReference用于Loan对象中的Customer，并将@JsonBackReference用于Customer实体中的Loan属性.

Because you are using the @JsonBackReference on the Customer property in the Loan entity, the Customer object will not included in the serialization. Use the @JsonManagedReference for the Customer in the Loan object and use @JsonBackReference on the Loan property in the Customer entity.

这将序列化Loan实体的Customer属性.但是Customer对象序列化将不包含Loan属性.您需要选择关系的一侧进行序列化.

This will serialize the Customer property of your Loan entity. But the Customer object serialization will not contains the Loan property. You need to pick one side of the relationship to serialize.

要允许双方，请在您的实体中使用@JsonIdentityInfo批注，并删除@JsonBackReference和@JsonManagedReference.您的实体将类似于:

To allow both side, use @JsonIdentityInfo annotation in your entity and remove the @JsonBackReference and @JsonManagedReference. You entities will be something like:

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "customerId")
public class Customer implements Serializable {
    ...
}

@JsonIdentityInfo的property引用您的实体ID属性，对于Customer，这将是customerId.还要对Loan和Item执行此操作.

The property of the @JsonIdentityInfo refer to your entity id property, for Customer this will be customerId. Do this for Loan and Item also.

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