JPA/Hibernate, @Embedded and Enum

Question

我正在尝试将枚举作为嵌入值进行持久化（最好使用其字符串表示，但现在即使使用序数也可以）

该枚举：

@Embeddable
public enum DayOfTheWeek {
 SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY;

 public int toCalendar() throws EnumConstantNotPresentException{
  switch (this) {
  case SUNDAY:
   return Calendar.SUNDAY;
  case MONDAY:
   return Calendar.MONDAY;
  case TUESDAY:
   return Calendar.TUESDAY;
  case WEDNESDAY:
   return Calendar.WEDNESDAY;
  case THURSDAY:
   return Calendar.THURSDAY;
  case FRIDAY:
   return Calendar.FRIDAY;
  case SATURDAY:
   return Calendar.SATURDAY;
  }
  throw new EnumConstantNotPresentException(this.getClass(), "Unknown value ["+this.name()+"]");
 }

 public static DayOfTheWeek fromCalendarDay(int day) {
  switch (day) {
  case Calendar.SUNDAY:
   return SUNDAY;
  case Calendar.MONDAY:
   return MONDAY;
  case Calendar.TUESDAY:
   return TUESDAY;
  case Calendar.WEDNESDAY:
   return WEDNESDAY;
  case Calendar.THURSDAY:
   return THURSDAY;
  case Calendar.FRIDAY:
   return FRIDAY;
  case Calendar.SATURDAY:
   return SATURDAY;
  }
  return null;
 }

 public static DayOfTheWeek getByDate(Date date) {
  Calendar calendar = GregorianCalendar.getInstance();
  calendar.setTime(date);
  return fromCalendarDay(calendar.get(Calendar.DAY_OF_WEEK));
 }

 @Override
 /**
  * Should return the localized day of the week
  */
 public String toString() {
  Calendar c = new GregorianCalendar();
  c.set(Calendar.DAY_OF_WEEK, this.toCalendar());
  SimpleDateFormat sdf = (SimpleDateFormat) SimpleDateFormat
    .getInstance();
  sdf.applyPattern("EEEEEEEEEE");

  return sdf.format(c.getTime());
 }

}

这个类：

@Entity
public class Day implements Serializable {

 ...

 @Enumerated
 @Embedded
 private DayOfTheWeek dayOfTheWeek;

 ...

 @Id
 @GeneratedValue
 private Long id;

 public void setId(Long id) {
  this.id = id;
 }

 public Long getId() {
  return id;
 }

 public void setDayOfTheWeek(DayOfTheWeek dayOfTheWeek) {
  this.dayOfTheWeek = dayOfTheWeek;
 }

 public DayOfTheWeek getDayOfTheWeek() {
  return dayOfTheWeek;
 }

 ...
}

现在，当持久化“Day”时，这个堆栈的有趣部分如下：

org.springframework.orm.hibernate3.HibernateSystemException: No default constructor for entity: xxx.yyyy.zzz.DayOfTheWeek; nested exception is org.hibernate.InstantiationException: No default constructor for entity: xxx.yyyy.zzz.DayOfTheWeek

我尝试了几种方法，但无论如何都无法使其正常工作，有什么想法吗？

- temsa

Answer 1

移除@Embedded和@Embeddable注释，只需使用@Enumerated(EnumType.STRING)将其作为字符串获取。

另外注意，考虑按照以下方式定义您的枚举以避免使用开关语句。

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public enum DayOfTheWeek {
    SUNDAY {
        @Override
        public int toCalendar() {
            return Calendar.SUNDAY;
        }

    },
    MONDAY {
        @Override
        public int toCalendar() {
            return Calendar.MONDAY;
        }
    },
    TUESDAY {
        @Override
        public int toCalendar() {
            return Calendar.TUESDAY;
        }
    },
    WEDNESDAY {
        @Override
        public int toCalendar() {
            return Calendar.WEDNESDAY;
        }
    },
    THURSDAY {
        @Override
        public int toCalendar() {
            return Calendar.THURSDAY;
        }
    },
    FRIDAY {
        @Override
        public int toCalendar() {
            return Calendar.FRIDAY;
        }
    },
    SATURDAY {
        @Override
        public int toCalendar() {
            return Calendar.SATURDAY;
        }
    };

    public abstract int toCalendar();

    public static DayOfTheWeek fromCalendarDay(int day) {

        for (DayOfTheWeek dayOfWeek : DayOfTheWeek.values()) {
            if (dayOfWeek.toCalendar() == day) {
                return dayOfWeek;
            }
        }

        return null; // Consider throwing IllegalArgumentException
    }

    public static DayOfTheWeek getByDate(Date date) {
        Calendar calendar = GregorianCalendar.getInstance();
        calendar.setTime(date);
        return fromCalendarDay(calendar.get(Calendar.DAY_OF_WEEK));
    }

    @Override
    /*
     * Should return the localized day of the week
     */
    public String toString() {
        Calendar c = new GregorianCalendar();
        c.set(Calendar.DAY_OF_WEEK, this.toCalendar());
        SimpleDateFormat sdf = (SimpleDateFormat) SimpleDateFormat
                .getInstance();
        sdf.applyPattern("EEEEEEEEEE");

        return sdf.format(c.getTime());
    }

}

- Lombo

---

使用字段会比编写返回常量值的 toCalendar() 更好。 - Jimmy T.

Answer 2

为什么你希望将枚举声明为@Embeddable。直接将其注解为列有什么问题吗？

@Enumerated(EnumType.STRING)
@Column(name = "...")
public DayOfTheWeek getDayOfTheWeek() {
    return dayOfTheWeek;
}

- Grzegorz Oledzki

Answer 3

我知道这个问题已经被回答了，而且很久以前就有了答案。

我只是想进一步提出对你的枚举结构的增强建议。以下是建议内容：

    public enum DayOfTheWeek {
        SUNDAY(Calendar.SUNDAY),
        MONDAY(Calendar.MONDAY),
        TUESDAY(Calendar.TUESDAY),
        WEDNESDAY(Calendar.WEDNESDAY),
        THURSDAY(Calendar.THURSDAY),
        FRIDAY(Calendar.FRIDAY),
        SATURDAY(Calendar.SATURDAY);

        DayOfTheWeek(int dayOfTheWeek){
            this.dayOfTheWeek = dayOfTheWeek;
        }
        int dayOfTheWeek;

        public int toCalendar(){
            return dayOfTheWeek;
        }

    }

感谢大家的关注！祝你们玩得愉快！

- Majki