Hibernate 一對一唯一外鍵關聯註解配置詳解：以 Husband-Wife 為例

表結構

Husband (husband_id PK, name)
Wife    (wife_id PK, name, husband_id FK UNIQUE)

業務規則：一個丈夫對應一個妻子，妻子表持有丈夫外鍵且唯一。

實體類註解

Husband 端（被引用方）

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

    private String name;

    @OneToOne(mappedBy = "husband", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Wife wife; // 可選：雙向導航

    // getters/setters
}

Wife 端（外鍵持有方）

@Entity
@Table(name = "Wife",
    uniqueConstraints = @UniqueConstraint(columnNames = "husband_id")
)
public class Wife {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "wife_id")
    private Long id;

    private String name;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "husband_id", nullable = false, unique = true)
    private Husband husband;

    // getters/setters
}

關鍵註解解析

雙向關聯維護最佳實踐

public class Husband {
    // ...
    public void setWife(Wife wife) {
        if (wife == null) {
            if (this.wife != null) this.wife.setHusband(null);
        } else {
            wife.setHusband(this);
        }
        this.wife = wife;
    }
}

public class Wife {
    // ...
    public void setHusband(Husband husband) {
        this.husband = husband;
    }
}

統一由 Husband 端管理關聯，避免雙向同步混亂。

常見問題與解決

1. 雙向無限遞歸序列化：Jackson 加 @JsonManagedReference / @JsonBackReference 或 @JsonIgnore。
2. 延遲加載異常：事務外訪問 wife.husband，確保 @Transactional 範圍或用 fetch = FetchType.EAGER (慎用)。
3. 外鍵列名不一致：@JoinColumn(name="husband_id", referencedColumnName="husband_id") 顯式指定。
4. 共享主鍵策略：若 Wife 共享 Husband PK，改用 @MapsId + @OneToOne，不再需要 @JoinColumn。

DDL 驗證

CREATE TABLE Husband (
    husband_id BIGINT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50)
);

CREATE TABLE Wife (
    wife_id BIGINT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50),
    husband_id BIGINT NOT NULL UNIQUE,
    FOREIGN KEY (husband_id) REFERENCES Husband(husband_id)
);

參考資源

• Hibernate 官方文檔：One-to-One Associations
• 推薦博文：Hibernate 一對一唯一外鍵註解詳解

掌握 @JoinColumn(unique=true) + mappedBy 雙向配置，即可優雅實現一對一唯一外鍵關聯。