最簡易清晰明瞭的hibernate雙向多對一註解配置

網上亂七八糟的太亂！各種不能用，各種錯！

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本博文實現：雙向多對一註解配置，在多端維護關係（在多端set一端），刪除多端不影響一端，刪除一端級聯刪除多端

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// 一的一端
@Entity
@Table(name = "one")
public class OneModel {

    @Id
    @GeneratedValue(generator = "generator")
    @GenericGenerator(name = "generator", strategy = "uuid")
    @Column(name = "id", length = 36)
    private String id;

    @OneToMany(mappedBy = "one", orphanRemoval = true)
    Set<ManyModel> manySet = new TreeSet<>();

}

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// 多的一端
@Entity
@Table(name = "many")
public class ManyModel {

    @Id
    @GeneratedValue(generator = "generator")
    @GenericGenerator(name = "generator", strategy = "uuid")
    @Column(name = "id", length = 36)
    private String id;

    @ManyToOne
    @JoinColumn(name = "one_id")
    private OneModel one;

}

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        // 如何關聯

        // 首先創建一端的對象
        OneModel one = new OneModel();
        svc.addOne(one);

        // 創建一個多端對象，並set進一端對象
        ManyModel many1 = new ManyModel();
        many1.setOne(one);
        svc.addMany(many1);

        // 再創建一個多端對象，並set進一端對象
        ManyModel many2 = new ManyModel();
        many2.setOne(one);
        svc.addMany(many2);

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通過上述操作之後，就實現了雙向多對一關聯，通過互相get即可取出對應關聯對象或對象集合。

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若要刪除一端，還保留多端數據，則需要如下配置：

    @OneToMany(mappedBy = "one", orphanRemoval = false)
    Set<ManyModel> manySet = new TreeSet<>();

    OneModel one = svc.getOneById("abc");

    one.getManySet().forEach(m -> m.setOne(null));

    svc.deleteOne(one);

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補充一個問題：如果用的SpringMVC , 可能在返回頁面一端數據時會報錯，需要在一端添加JsonIgnore註釋 ，也就是不將多端集合json序列化

    @OneToMany(mappedBy = "one")
    @JsonIgnore // 加上該註釋即可
    private Set<ManyModel> manySet = new TreeSet<>();