如何在数据库中保存没有实体的对象

Question

实体"schoolyear"具有可配置的可见工作日,在时间规划器中可见或不可见.

我现在看到2个posibilites来保存可见的工作日.

要么我建立N:M关系:N schoolyear有M VisibleWeekDays

或者我将可见的周日放在逗号分隔的字段中:"0,2,5"

这些数字是DayOfWeek枚举中的枚举值.

我是否应该真正去创建另外两个表(结点+ VisibleWeekDay表)的开销方式,只是为了在一个字段中保存一天的索引？

你会如何保存那些可见的工作日？

Answer 1

DB字段中的逗号分离会伤害我的感受.考虑一下位掩码:

[Flags]
public enum DayOfWeek
{
   Undefined = 0,
   Mon = 1,
   Tue = 2,
   Wed = 4,
   Thu = 8,
   Fri = 16,
   Sat = 32,
   Sun = 64
}

DayOfWeek bitmask = DayOfWeek.Mon | DayOfWeek.Wed | DayOfWeek.Sat;

这样您就可以保持理智和查询能力.

要在SQL中查询:

DECLARE @bitmast INT;
SET @bitmask = 64 | 1 | 16; -- sun, mon, fri

SELECT * FROM tbl
WHERE DayOfWeekBitMask & @bitmask = @bitmask;

要使用LINQ to Entities进行查询:

int bitmask = DayOfWeek.Sun | DayOfWeek.Mon |DayOfWeek.Fri;
var query = Context.tbl.Where(r => (r.DayOfWeekBitMask & bitmask) == bitmask);

坚持:

int bitmask = DayOfWeek.Sun | DayOfWeek.Mon |DayOfWeek.Fri;
var item = Context.tbl.First();

item.DayOfWeekBitMask = bitmask;
Context.SaveChanges();