java如何使用Hibernate注释

Question

我在DB中有以下表格： Tables

并希望hibernate@Entity进行如下POJO那样的交换：

class ExchangeRates{
    List<Currency> currencies;
}

class Currency{
    Long Id;
    String name;
    List<Rate> exchangeRates;
}

class Rate{
    Currency currency;
    BibDecimal rate;
}

你能给我一些关于如何使用hibernate注释的建议吗

Answer 1

如果有两个Entities具有ManyToMany关系，那么将有一个引用这两个关系的JoinTable

例如，该表将如下所示：

Name: EX_CUR
Column 1:CUR_ID
Column 2:EX_ID

而像这样的实体：

@Entity
@Table(name="currencies_fixed_exchange_rates")
class ExchangeRates{

    @Id
    Long id;

    @ManyToMany
    @JoinTable(
      name="EX_CUR",
      joinColumns=@JoinColumn(name="CUR_ID", 
      referencedColumnName="ID"),
      inverseJoinColumns=@JoinColumn(name="EX_ID", 
      referencedColumnName="ID"))
    List<Currency> currencies;
}

@Entity
@Table(name="currencies")
class Currency{

    @Id
    Long Id;

    @Column
    String name;

    @ManyToMany(mappedBy="currencies")
    List<Rate> exchangeRates;
}

@Entity
@Table
class Rate{

    @Id
    Long id;

    @OneToOne
    Currency currency;

    @Column
    BigDecimal rate;
}