NHibernate：如何使用带有本机 SQL 的 CreateSQLQuery 返回标量值？

Question

I'm trying to get a scalar value using a native SQL query and my statement looks like

var deptName =session.CreateSQLQuery(@"Select d.deptName from employee e,dept d Where e.deptId=d.deptID and e.EmpID=?")
                    .AddScalar("deptName", NHibernateUtil.String)
                    .SetCacheable(true)
                    .SetCacheMode(CacheMode.Normal)
                    .SetParameter(0, "12345").List();

And the corresponding SQL from SQL Server Profiler is correct and it is returning the desired value

exec sp_executesql N'select d.deptName from employee e, dept d
                            where e.empId=@p0 
                            and e.deptId=d.deptId',N'@p0 nvarchar(4000)',@p0=N'12345'

But the typeof deptName is System.Collections.IList {System.Collections.Generic.List<object>} and also when I try to access the deptName with deptName[0].ToString() it is returning System.Object[] instead of the actual value.

Answer 1

你需要告诉它你只想要标量：

var deptName = session.CreateSQLQuery("...").UniqueResult<string>();

Answer 2

Your code is all correct, but at the end while returning the value, you are converting the scalar output to list. Observe the .List() at the end of your code. That is the problem.

Though your SQL query selects only one column from one row, NHibernate have no way to learn that that is the case. You can instruct NHibernate to convert the output to scalar value by replacing .List() call with .UniqueResult<string>() call.

The .UniqueResult<string>() call is again two fold. The UniqueResult will not return scalar, it may return single row (entity instance) based on generic parameter passed to it. If no matching row found, it will return null . If multiple rows found, it will throw NonUniqueResultException as seen in the source code here :

 internal static object UniqueElement(IList list) { int size = list.Count; if (size == 0) { return null; } object first = list[0]; for (int i = 1; i < size; i++) { if (list[i] != first) { throw new NonUniqueResultException(size); } } return first; }

Further, to make it return single scalar value instead of row, you need to use generic overload UniqueResult<T> . You need to specify generic parameter ( <string> in your case; depends on what you are returning) to it.