GregorianCalendar field not being converted to Date through TypeConverter

Question

My TypeConverter is not working for converting GregorianCalendar to an sql Date type. An error is being thrown on the following code:

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

Error:(42, 31) error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.

The TypeConverter code:

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());
}

}

Answer 1

Room can only store simple data types, you need to provide a type converter for Date (or change your converter to convert Calender to 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();
    }
}

Or something like this:

 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();
}