Question

我正试图通过此代码QueryOver和RowCount从员工处获取所有活动任务：

 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()会返回0。问题是我需要知道员工是否不存在或者是否没有活动任务。

我可以使用2个查询执行此操作，我首先获取员工并检查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。

Answer 1

使用LINQ to NHibernate可以更简单：

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() 
        });

这将仅返回具有适当数量任务的现有员工。如果员工不存在，则返回空集合。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

1 个答案: