涉及的表:
Cake{
Id ,
CakeName

}

CakeSize{

CakeId,-为外键,对应Cake表的字段Id

Size

}

(其中ISession session = NHibernateHelper.GetCurrentSession();)

用法一(返回数值):
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>;//使用此方法发现sql执行了两次,故不推荐使用。

 用法二(返回对象实体):
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(连表查询):
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>();

以上是一种常见的用法,通过该例子,相信大家心里也已经有个数了,也应该知道怎么操作这个sql了:)

但是过程中难免会遇到些问题,比如:

实例二(问题说明):

我需要执行例如这条sql语句:

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方法执行的话,你可能会遇到这样的错误:

错误: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方法执行:

错误: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方法并指定返回字段值的类型,即使用AddScalar方法指定字段值类型:

错误: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字段对应数据库的类型是int,这里我就误解为也应该映射为NHibernateUtil.Int32;

4. 解决问题:

把AddScalar方法的参数里一个属性改了一下:

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:这里我将EmailType的类型映射改为了NHibernateUtil.String,实际上是与返回结果的EmailType值类型保持一致就OK了。

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