為什么雙向多對一會導致Hibernate中的回圈依賴？

我的專案中有物體（基于Spring-Boot Hibernate）：

@Entity
@Table(name = "user_account")
public class UserAccount {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @NotNull
    @Column(name = "username")
    private String userName;

    @NotNull
    @Column(name = "first_name")
    private String firstName;

    @NotNull
    @Column(name = "last_name")
    private String lastName;

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

    @CreationTimestamp
    @Column(name = "birthday")
    private LocalDateTime birthday;

    @NotNull
    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "role", referencedColumnName = "id")
    private UserRole role;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "userAccount", cascade= CascadeType.ALL)
    private Set<RentInfo> rents;
}

和

@Entity
@Table(name = "rent_info")
public class RentInfo {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @NotNull
    @ManyToOne(cascade= CascadeType.ALL)
    @JoinColumn(name="user_id")
    private UserAccount userAccount;

    @CreationTimestamp
    @Column(name = "start_date")
    private LocalDateTime startDate;

    @CreationTimestamp
    @Column(name = "end_date")
    private LocalDateTime endDate;

    @Column(name = "status")
    private int status;
}

我想創建雙向一對多關系，當一個用戶可以有多個租金時，我們可以通過具體的 user_id 選擇租金，但是出了點問題

作為回應，我得到了這個：

{
        "id": 1,
        "userName": "[email protected]",
        "firstName": "fName",
        "lastName": "lName",
        "password": "test",
        "birthday": "2001-11-03T14:28:14",
        "role": {
            "name": "CLIENT"
        },
        "rents": [
            {
                "userAccount": {
                    "id": 1,
                    "userName": "[email protected]",
                    "firstName": "fName",
                    "lastName": "lName",
                    "password": "test",
                    "birthday": "2001-11-03T14:28:14",
                    "role": {
                        "name": "CLIENT"
                    },
                    "rents": [
                        {
                            "userAccount": {
                                "id": 1,
                                "userName": "[email protected]",
                                "firstName": "fName",
                                "lastName": "lName",
                                "password": "test",
                                "birthday": "2001-11-03T14:28:14",
                                "role": {
                                    "name": "CLIENT"
                                }
    .....

這是無限的，邏輯上我有記憶體不足錯誤。我怎樣才能解決這個問題？我做錯了什么？

uj5u.com熱心網友回復：

您有兩種解決方案：

1. 在 @ManyToOne 上使用 @JsonIgnore
2. 不要序列化您的物體。改用 DTO 并在映射時注意避免回圈依賴

uj5u.com熱心網友回復：

您還可以使用@JsonManagedReference和@JsonBackReference來解決這個無限遞回問題，如下所示：

@Entity
@Table(name = "user_account")
public class UserAccount {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @NotNull
    @Column(name = "username")
    private String userName;

    @NotNull
    @Column(name = "first_name")
    private String firstName;

    @NotNull
    @Column(name = "last_name")
    private String lastName;

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

    @CreationTimestamp
    @Column(name = "birthday")
    private LocalDateTime birthday;

    @NotNull
    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "role", referencedColumnName = "id")
    private UserRole role;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "userAccount", cascade= CascadeType.ALL)
    @JsonManagedReference
    private Set<RentInfo> rents;
}

@Entity
@Table(name = "rent_info")
public class RentInfo {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @NotNull
    @ManyToOne(cascade= CascadeType.ALL)
    @JoinColumn(name="user_id")
    @JsonBackReference
    private UserAccount userAccount;

    @CreationTimestamp
    @Column(name = "start_date")
    private LocalDateTime startDate;

    @CreationTimestamp
    @Column(name = "end_date")
    private LocalDateTime endDate;

    @Column(name = "status")
    private int status;
}

不過，我會首先將您的物體映射到 DTO。但是，你還不如需要使用@JsonManagedReference，并@JsonBackReference在這些新的DTO類，如果你想要的所有資料可用（避免這一無限遞回問題將是未映單向userAccount的RentInfoDto，但你可能不希望這樣，因為你也想序列UserAccountDto資料）。

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