您不需要在visitdate类中创建单独的字段“subscription”。hibernate将自动创建一个字段来存储订阅id。代码需要稍微更改。

@Entity
@Table(name = "subscription")
public class Subscription {

  @Id
  @GeneratedValue(strategy= GenerationType.IDENTITY)
  @Column(name = "subscription_id")
  private long id;

  @Column(name = "userid", nullable = false)
  private String userId;

  @Column(name = "saledate", nullable = false)
  @Temporal(TemporalType.DATE)
  private Date saleDate;

  @Column(name = "finishdate", nullable = false)
  @Temporal(TemporalType.DATE)
  private Date finishDate;

  @Column(name = "price", nullable = false)
  private long price;

  @Column(name = "description", nullable = false)
  private String description;

  @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "associatedSub")
  private List<VisitDate> visitDates = new ArrayList<>();
}

请注意，我已将mappedby属性更改为指向上述类中的associatedsub。

@Entity
@Table(name="visitdate")

public class VisitDate {
  @Id
  @GeneratedValue(strategy= GenerationType.IDENTITY)
  @Column(name = "id")
  private long id;

  @Column(name = "date", nullable = false)
  @Temporal(TemporalType.DATE)
  private Date         date;

  @ManyToOne
  @JoinColumn(name="subscription_id")
  private Subscription associatedSub;
}

你可以使用单向关系来达到同样的目的。您只需要为特定的订阅添加一个访问列表/访问集，而不必为特定的访问创建一个订阅列表。参考请访问[java jpa]：(https://en.wikibooks.org/wiki/java_persistence/onetomany#undirectional_onetomany.2c_no_inverse_manytoone.2c_no_join_table_.28jpa_2.0_only.29)!

@Entity
@Table(name = "subscription")
@Proxy(lazy = false)
public class Subscription {

@Id @GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "subscription_id")
private long id;

@Column(name = "userid", nullable = false)
private String userId;

@Column(name = "saledate", nullable = false)
@Temporal(TemporalType.DATE)
private Date saleDate;

@Column(name = "finishdate", nullable = false)
@Temporal(TemporalType.DATE)
private Date finishDate;

@Column(name = "price", nullable = false)
private long price;

@Column(name = "description", nullable = false)
private String description;

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "subscription")
private List<VisitDate> visitDates = new ArrayList<>();
}

@Entity
@Table(name="visitdate")

public class VisitDate {
@Id 
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name = "id")
private long id;

private long subscription;

@Column(name = "date", nullable = false)
@Temporal(TemporalType.DATE)
private Date date;
}