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我无法与@EmbeddedId在最后一个实体中使用的持久三个级别的实体进行级联合并。我有以下三个实体：
1. Voucher
2. Rate
3. RatePerChannelOverwrite

由Voucher服务获取。然后我想Rate在凭证中添加新的。然后我想RatePerChannelOverwrite在Rate. 所以两者都Rate将RatePerChannelOverwrite它们@Id作为NULL。这是有效的。

但是后来我尝试RatePerChannelOverwrite分成两个班级并拥有：@Embeddable RatePerChannelOverwriteId. 这个设置失败了。被Rate引用的对象RatePerChannelOverwriteId永远不会填充其新 ID。

@Entity
public class Voucher {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Integer id;

    @OneToMany(mappedBy = "voucher", fetch = FetchType.LAZY, orphanRemoval = true, cascade = CascadeType.ALL)
    private Set<Rate> rates = new HashSet<Rate>();
}

@Entity
public class Rate {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Integer id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "voucher_id", referencedColumnName = "id")
    private Voucher voucher;

    @Column(name = "rate", precision = 2, scale = 9, columnDefinition = "decimal")
    @NumberFormat(pattern = "#0.00")
    private double rate;

    @OneToMany(mappedBy = "rate", fetch = FetchType.EAGER, orphanRemoval = true, cascade = CascadeType.ALL)
    private Set<RatePerChannelOverwrite> ratePerChannelOverwrites;
}

@Entity
public class RatePerChannelOverwrite {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Integer id;

    @ManyToOne
    @JoinColumn(name = "rate_id", referencedColumnName = "id")
    private Rate rate;

    @Column(name = "channel_id")
    private Integer channelId;

    @Column(name = "rate", precision = 2, scale = 9, columnDefinition = "decimal")
    @NumberFormat(pattern = "#0.00")
    private double rate;
}

当我做这样的事情时，这很好用：

Voucher voucher = service.getVoucher(123456); 
Rate rate = new Rate(); //NOTE ID IS NULL HERE
rate.setVoucher(voucher);
voucher.getRates().add(rate);

RatePerChannelOverwrite channelRate = new RatePerChannelOverwrite();
channelRate.setRate(rate);
rate.getRatePerChannelOverwrites.add(channelRate);   

voucher = voucher.merge();

但是，当我将最后一个实体分成 2 个单独的类时，idinrate始终RatePerChannelOverwriteId为 NULL。不知何故，这里的级联失败了。

注意：第三个实体具有与 一样@EmbeddedId的复合键@ManyToOne，这就是问题出现的地方。

@Embeddable
public class RatePerChannelOverwriteId {
    @ManyToOne
    @JoinColumn(name = "rate_id", referencedColumnName = "id")
    private Rate rate;

    @Column(name = "channel_id")
    private Integer channelId;
}

@Entity
public class RatePerChannelOverwrite {
    @EmbeddedId
    private RatePerChannelOverwriteId id;

    @Column(name = "rate", precision = 2, scale = 9, columnDefinition = "decimal")
    @NumberFormat(pattern = "#0.00")
    private double rate;
}

这样做是否正确？

Voucher voucher = service.getVoucher(123456);   
Rate rate = new Rate();
rate.setVoucher(voucher);
voucher.getRates().add(rate);

RatePerChannelOverwriteId channelRateId = new RatePerChannelOverwriteId();
channelRateId.setRate(rate);   
RatePerChannelOverwrite channelRate = new RatePerChannelOverwrite();
channelRate.setId(channelRateId);
rate.getRatePerChannelOverwrites.add(channelRate);   

voucher = voucher.merge();

我得到的实际异常是来自 'org.hibernate.type.descriptor.AbstractTypeDescriptor.extractHashCode(T value)' 的 NullPointer，其中 value 为 NULL，因为idinRate仍然为 NULL（尽管 SQL 跟踪显示 INSERT 是在 上执行的Rate）。

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