避免对hibernate的循环依赖

Question

package com.example.demo.model;

import com.sun.istack.NotNull;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.data.jpa.domain.support.AuditingEntityListener;

import javax.persistence.*;
import java.util.*;

@Data
@NoArgsConstructor
@AllArgsConstructor
@Entity
@EntityListeners(AuditingEntityListener.class)
@Table(name="MEDICAL_DEVICE")
public class MedicalDevice {

    public MedicalDevice(UUID deviceId, DefectPriority defectPriority, State currentState) {
        this.deviceId = deviceId;
        this.defectPriority = defectPriority;
        this.currentState = currentState;
    }

    public MedicalDevice(UUID deviceId, State currentState) {
        this.deviceId = deviceId;
        this.currentState = currentState;
    }

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

    @Column(name="DEVICE_ID")
    @NotNull
    private UUID deviceId;

    @Column(name="DEFECT_PRIORITY", nullable = true)
    @Enumerated(EnumType.STRING)
    private DefectPriority defectPriority;

    @OneToMany(mappedBy="medicalDevice")
    private List<State> states = new ArrayList<>();

    @OneToOne(mappedBy="medicalDevice")
    private State currentState;



}

package com.example.demo.model;

import com.sun.istack.NotNull;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.NonNull;
import org.springframework.data.jpa.domain.support.AuditingEntityListener;

import javax.persistence.*;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.util.List;
import java.util.UUID;

@Data
@NoArgsConstructor
@AllArgsConstructor
@Entity
@EntityListeners(AuditingEntityListener.class)
@Table(name="STATE")
public class State {

    public State(StateNames state, UUID enteredBy, LocalDateTime enteredAt) {
        this.state = state;
        this.enteredBy = enteredBy;
        this.enteredAt = enteredAt;
    }

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

    @Enumerated(EnumType.STRING)
    private StateNames state;

    @Column(name="USER_ID")
    private UUID enteredBy;       //User who changed the devices state to this one

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="MEDICAL_DEVICE_ID")
    @NotNull
    private MedicalDevice medicalDevice;



    @Column(name = "LOCAL_DATE_TIME", columnDefinition = "TIMESTAMP")
    private LocalDateTime enteredAt;    //Time when the devices state was changed into this one

    @Column(name = "LOCAL_DATE", columnDefinition = "DATE")
    private LocalDate availabilityDate; //Date when a device will be available (only used in defect states and bought state)

    @OneToMany(mappedBy="state")
    private List<AdditionalInformation> additionalInformation;


}

如何避免State类和MedicalDevice类之间对hibernate的循环依赖？我已经实现了@OneToMany List和@OneToOne state currentState，前者是旧状态，后者表示当前状态。我希望将它们分开，不是列表中的全部，而是我的实现会导致that> enter image description here

Answer 1

使用@JsonIgnore批注在State类中批注MedicalAdvice对象。这样，您就可以防止从实体类之间的关系中无限递归地获取数据。

Answer 2

您没有提供错误消息，因此很难确切知道是什么导致了循环依赖，但基本思想是，它源于MedicalDevice对State的引用，反之亦然，因此两者相互依赖。

(顺便说一下，您还将MedicalDevice设置为具有@OneToMany关系的State列表，以及具有@OneToOne关系的State实例。这并不是真的有效，要么是@OneToMany，要么是@OneToOne。换句话说，MedicalDevice要么只有一个State，要么有多个State，但并不是两者都有。我不知道这是否导致了您的问题)。

在任何情况下，循环依赖都可能是由于被调用的equals/hashcode或toString方法造成的。MedicalDevice可能会在其State变量上调用这些方法，而后者将在其MedicalDevice变量上调用该方法，依此类推。

一种可能的解决方案是排除equals/hashcode和toString方法中的引用。但是再说一次，如果没有错误的细节，很难说出确切的问题是什么。