涉及的表：
Cake{
Id ，
CakeName
}
CakeSize{
CakeId，-為外鍵，對應Cake表的字段Id
Size
}
（其中ISession session = NHibernateHelper.GetCurrentSession();）
用法一（返回數值）：
ISQLQuery query = session.CreateSQLQuery("SELECT COUNT(Id) AS C FROM Cake").AddScalar("C", NHibernateUtil.Int32);
int c = Convert.ToInt32(query.UniqueResult());
或int c = query.UniqueResult<int>;//使用此方法發現sql執行了兩次，故不推薦使用。
用法二（返回對象實體）：
ISQLQuery query = session.CreateSQLQuery("select * from cake c").AddEntity("CAKE.DataTransfer.Entities.Cake");
或ISQLQuery query = session.CreateSQLQuery("select * from cake c").AddEntity("c", "CAKE.DataTransfer.Entities.Cake");
或ISQLQuery query = session.CreateSQLQuery("select * from cake c").AddEntity(typeof(Cake));
或ISQLQuery query = session.CreateSQLQuery("select * from cake c").AddEntity("c", typeof(Cake));
或ISQLQuery query = session.CreateSQLQuery("select * from cake c").AddEntity("c", typeof(Cake), LockMode.Write);
IList<Cake> c = query.List<Cake>();
用法三（連表查詢）：
ISQLQuery query = session.CreateSQLQuery("select cs.* from cake c join CakeSize cs on cs.CakeId=c.Id")
.AddEntity("cs", typeof(CakeSize));
IList<CakeSize> cs = query.List<CakeSize>();
以上是一種常見的用法，通過該例子，相信大家心里也已經有個數了，也應該知道怎么操作這個sql了：）
但是過程中難免會遇到些問題，比如：
實例二（問題說明）：
我需要執行例如這條sql語句：
select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo
1. 如果使用session.CreateQuery方法執行的話，你可能會遇到這樣的錯誤：
錯誤：undefined alias or unknown mapping
ISession session = DAORepository.Instrance.DbSession;
string queryString = "select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo where status=0 Order by CreateTime desc";
IQuery query = session.CreateQuery(queryString;
IList lst = query.List();
2. 使用CreateSQLQuery方法執行：
錯誤：Return types of SQL query were not specified...
ISession session = DAORepository.Instrance.DbSession;
string queryString = "select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo where status=0 Order by CreateTime desc";
ISQLQuery query = session.CreateSQLQuery(queryString);
IList lst = query.List();
3. 使用CreateSQLQuery方法並指定返回字段值的類型，即使用AddScalar方法指定字段值類型：
錯誤：could not execute query...
ISession session = DAORepository.Instrance.DbSession;
string queryString = "select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo where status=0 Order by CreateTime desc";
ISQLQuery query = session.CreateSQLQuery(queryString).AddScalar("CreateTime",NHibernateUtil.String)
.AddScalar("Address",NHibernateUtil.String)
.AddScalar("Password",NHibernateUtil.String)
.AddScalar("EmailType",NHibernateUtil.Int32);
IList lst = query.List();
ISession session = DAORepository.Instrance.DbSession;
string queryString = "select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo where status=0 Order by CreateTime desc";
ISQLQuery query = session.CreateSQLQuery(queryString).AddScalar("CreateTime",NHibernateUtil.String)
.AddScalar("Address",NHibernateUtil.String)
.AddScalar("Password",NHibernateUtil.String)
.AddScalar("EmailType",NHibernateUtil.Int32);
IList lst = query.List();
注意：EmailType字段對應數據庫的類型是int，這里我就誤解為也應該映射為NHibernateUtil.Int32；
4. 解決問題：
把AddScalar方法的參數里一個屬性改了一下：
ISession session = DAORepository.Instrance.DbSession;
string queryString = "select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo where status=0 Order by CreateTime desc";
ISQLQuery query = session.CreateSQLQuery(queryString).AddScalar("CreateTime",NHibernateUtil.String)
.AddScalar("Address",NHibernateUtil.String)
.AddScalar("Password",NHibernateUtil.String)
.AddScalar("EmailType",NHibernateUtil.String);
IList lst = query.List();
ISession session = DAORepository.Instrance.DbSession;
string queryString = "select CreateTime,Address,Password, (case when EmailType = 0 then 'Gmail' when EmailType = 1 then 'Yahoo' when EmailType = 2 then 'Hotmail' else 'Other' end) as EmailType from MailInfo where status=0 Order by CreateTime desc";
ISQLQuery query = session.CreateSQLQuery(queryString).AddScalar("CreateTime",NHibernateUtil.String)
.AddScalar("Address",NHibernateUtil.String)
.AddScalar("Password",NHibernateUtil.String)
.AddScalar("EmailType",NHibernateUtil.String);
IList lst = query.List();
注意：這里我將EmailType的類型映射改為了NHibernateUtil.String，實際上是與返回結果的EmailType值類型保持一致就OK了。