GregorianCalendar 字段未通过 TypeConverter 转换为 Date

Posted 2023-03-24

【中文标题】GregorianCalendar 字段未通过 TypeConverter 转换为 Date

【英文标题】：GregorianCalendar field not being converted to Date through TypeConverter

【发布时间】：2018-08-14 14:51:13

【问题描述】：

我的 TypeConverter 无法将 GregorianCalendar 转换为 sql Date 类型。以下代码出现错误：

/** due date of item */
@TypeConverters(CalendarConverter.class)
private GregorianCalendar dueDate = null;

错误：(42, 31) 错误：无法弄清楚如何将此字段保存到数据库中。您可以考虑为其添加类型转换器。

TypeConverter 代码：

public class CalendarConverter 

@TypeConverter
public static GregorianCalendar fromDate(Date value)
    if(value == null)
        throw new NullPointerException("must not be null");
    
    GregorianCalendar cal = new GregorianCalendar();
    cal.setTime(value);
    return cal;


@TypeConverter
public static Date toDate(GregorianCalendar calendar)
    if(calendar != null)
        throw new NullPointerException("must not be null");
    
    Calendar cal = calendar;
    return new Date(cal.getTime().getTime());

【参考方案1】：

Room只能存储简单的数据类型，你需要提供一个Date的类型转换器（或者改变你的转换器将Calender转换为Long）：

@TypeConverter
public Date fromTimestamp(Long value) 
    return value == null ? null : new Date(value);


@TypeConverter
public Long dateToTimestamp(Date date) 
    if (date == null) 
        return null;
     else 
        return date.getTime();
    

或者是这样的：

 public class CalendarConverter 

@TypeConverter
public static GregorianCalendar fromLong(Long value)
    if(value == null)
        throw new NullPointerException("must not be null");
    
    GregorianCalendar cal = new GregorianCalendar();
    cal.setTime(new Date(value));
    return cal;


@TypeConverter
public static Long toLong(GregorianCalendar calendar)
    if(calendar != null)
        throw new NullPointerException("must not be null");
    
    Calendar cal = calendar;
    return cal.getTime();