.NET中的枚举我们一般有两种用法，一是表示唯一的元素序列；还有就是用来表示多种复合的状态。这个时候一般需要为枚举加上[Flags]特性标记为位域,这样我们就可以用"或"运算符组合多个状态.

例如：

[Flags]
public enum Permission
{
create = 1,
read = 2,
update = 4,
delete = 8,
}



Permission permission = Permission.create | Permission.read | Permission.update | Permission.delete;
Console.WriteLine("1、枚举创建，并赋值……");
Console.WriteLine(permission.ToString());
Console.WriteLine((int)permission);

permission = (Permission)Enum.Parse(typeof(Permission), "5");
Console.WriteLine("2、通过数字字符串转换……");
Console.WriteLine(permission.ToString());
Console.WriteLine((int)permission);

permission = (Permission)Enum.Parse(typeof(Permission), "update, delete, read", true);
Console.WriteLine("3、通过枚举名称字符串转换……");
Console.WriteLine(permission.ToString());
Console.WriteLine((int)permission);

permission = (Permission)7;
Console.WriteLine("4、直接用数字强制转换……");
Console.WriteLine(permission.ToString());
Console.WriteLine((int)permission);

permission = permission & ~Permission.read;
Console.WriteLine("5、去掉一个枚举项……");
Console.WriteLine(permission.ToString());
Console.WriteLine((int)permission);

permission = permission|Permission.delete;
Console.WriteLine("6、加上一个枚举项……");
Console.WriteLine(permission.ToString());
Console.WriteLine((int)permission);


在数据库中判断： AND (@permission IS NULL OR @permission=0 OR permission &@permission =@permission)

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