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@ElementCollection//JPA通过@ElementCollection注解集合映射，可以自动检测元素类型
@MapKeyEnumerated(EnumType.STRING)//指定基本类型为枚举类型的映射键的枚举类型,MapKeyEnumerated注释可以应用于一个元素集合或类型的关系
private Map<AddressType, String> addresses = new HashMap<>();

@Version//JPA通过在实体类中使用@Version注解来发现数据库记录的并发操作,如果数据被修改，JPA会将这个字段自增，如果还有别的实体也在操作，它会抛出一个尝试提交的事务异常
private int version;

//Getters and setters are omitted for brevity

}

public enum AddressType {
HOME,
OFFICE
}

@Entity
public class Partner {

@Id
@GeneratedValue
private Long id;

private String name;

@Version
private int version;

//Getters and setters are omitted for brevity

}

@Entity
public class Phone {

@Id
private Long id;

@ManyToOne(fetch = FetchType.LAZY)//@ManyToOne用来配置多对一关联映射，表示在多的那一方通过延迟加载的方式加载对象(默认是非延迟加载)
private Person person;

@Column(name = “phone_number”)//@Column注解来标识实体类中属性与数据表中字段的对应关系
private String number;

@Enumerated(EnumType.STRING)
@Column(name = “phone_type”)
private PhoneType type;

@OneToMany(mappedBy = “phone”, cascade = CascadeType.ALL, orphanRemoval = true)// orphanRemoval 设置级联删除 ， true代表自动删除
private List calls = new ArrayList<>( );

@OneToMany(mappedBy = “phone”)
@MapKey(name = “timestamp”)//@MapKey指定了映射,持久化timestamp或者timestamp的值
@MapKeyTemporal(TemporalType.TIMESTAMP )//@MapKeyTemporal应用于java.util.map类型的元素集合或关系
private Map<Date, Call> callHistory = new HashMap<>();

@ElementCollection
private List repairTimestamps = new ArrayList<>( );

//Getters and setters are omitted for brevity

}

public enum PhoneType {
LAND_LINE,
MOBILE;
}

@Entity
@Table(name = “phone_call”)@Table用于指明数据库的表名,若不指定则以实体类名称作为表名
public class Call {

@Id
@GeneratedValue
private Long id;

@ManyToOne
private Phone phone;

@Column(name = “call_timestamp”)
private Date timestamp;

private int duration;

//Getters and setters are omitted for brevity

}

@Entity
@Inheritance(strategy = InheritanceType.JOINED)//@Inheritance定义继承的策略，有SINGLE_TABLE、TABLE_PER_CLASS 和 JOINED 三种，JOINED 是将父类、子类分别存放在不同的表中，并且建立相应的外键，以确定相互之间的关系
public class Payment {

@Id
@GeneratedValue
private Long id;

private BigDecimal amount;

private boolean completed;

@ManyToOne
private Person person;

//Getters and setters are omitted for brevity

}

@Entity
public class CreditCardPayment extends Payment {
}

@Entity
public class WireTransferPayment extends Payment {
}