NHibernate QueryOver RowCount，区分0和NULL

Question

我正在尝试通过 QueryOver 和 RowCount 获取员工的所有活动任务，代码如下：

 var id = 1;
 var activeTasks = Session
    .QueryOver<Employee>()
    .Where(emp => emp.id == id)
    .JoinQueryOver<Tasks>(emp => emp.Tasks, JoinType.InnerJoin)
    .Where(task => task.State == TaskState.Active)
    .RowCount();

如果没有指定id的员工，RowCount()returns0。问题是我需要知道该员工是否不存在或是否没有活动任务。

我可以用 2 个查询来做到这一点，我首先获取员工并检查是否为 null，然后查询任务。但理想情况下，如果可能的话，我希望这一切都在一个查询中完成。

Answer 1

您可以使用 LINQ to NHibernate 来更简单：

var employeeWithActiveTaskCount = session
    .Query<Employee>()
    .Where(e => e.Id == id)
    .GroupJoin(
        session
            .Query<Task>()
            .Where(t => t.State == TaskState.Active),
        e => e.Id,
        t => t.Employee.Id,
        (e, t) => new { Employee = e, Tasks = t })
    .Select(et => new 
        {
            EmployeeId = et.Employee.Id,
            TaskCount = et.Tasks.Count() 
        });

这将 return 只有具有适当数量任务的现有员工。如果员工不存在，则 returned 为空集合。由此生成的查询如下所示：

select employee0_.Id as col_0_0_, (select cast(count(*) as INT) 
    from [Task] task1_ where task1_.State=? 
    and (task1_.Employee_id=employee0_.Id
         or (task1_.Employee_id is null)
         and (employee0_.Id is null))) 
as col_1_0_ from [Employee] employee0_ where employee0_.Id=?

NHibernate QueryOver RowCount，区分0和NULL

NHibernate QueryOver RowCount, differentiate between 0 and NULL

c#

sqlite

nhibernate