nhibernate在使用过程中遇到问题，不断解决后的一些零碎知识：
一、Express:
Express声明一个变量后，此变量可以保存一个lamda表达式，Express exp=(o=>o.fieldname),这样可以动态组合要查询的字段。
上代码：
Expression<Func<Gx.Model.Author, bool>> where1, where2;
if (CityId != 0)
{
// strCity = " and other_City=" + CityId;
where1 = o => o.OtherCity == CityId;
}
else where1 = o => o.AuthorId != null;
if (Types)
{
//strPhoto = " and Photo1 is not null ";
where2 = o => o.Photo1 != null;
}
else where2 = o => o.AuthorId != null;
var list1 = new Author().CreateQueryOver().Where(where1)
.Where(where2)
.OrderBy(o=>o.AuthorId).Desc
.Take(NO)
.List<Gx.Model.Author>();//获取最新加入的成员
二、连表后，排序的问题。
IList<Gx.Model.MessageBoard> MessBoard = (from m in iq2
//from t in m.MessageBoards
// .OrderByDescending(o=>o.MessageBoards.Select(oo=>oo.MBMessageDate))
//from t in m.Orders
join m2 in iq
on m.AuthorId equals m2.Author.AuthorId into m3
from t in m3
orderby t.AuthorID
select new Gx.Model.MessageBoard { Mb_id = t.Mb_id, FromID = t.FromID, Realname = t.FromID != 0 ? t.Author.RealName : t.Realname, MBIP = t.FromID != 0 ? t.Author.OtherAddress : t.MBIP ,MBMessage=t.MBMessage,MBMessageDate=t.MBMessageDate, Author=t.Author})
//.Orderby(o=>o.AuthorID)
.Take(Count)
.ToList<Gx.Model.MessageBoard>();
像上面两处红色字体那样排序都会报错（Invalid Path）。
解决办法:
MessBoard=MessBoard..Orderby(o=>o.AuthorID).ToList();
三、nhibernate完成与case when相同的功能：
条件：必须在数据访问返回的是一个IQueryable,linq查询（方便）。
select new Gx.Model.MessageBoard { Mb_id = t.Mb_id, FromID = t.FromID, Realname = t.FromID != 0 ? t.Author.RealName : t.Realname, MBIP = t.FromID != 0 ? t.Author.OtherAddress : t.MBIP ,MBMessage=t.MBMessage,MBMessageDate=t.MBMessageDate, Author=t.Author})
以上，只是些零散的随笔。有不正确之处，批评指正。