list.longcount 使用连接查询 (Linq/Lambda)答案

【问题标题】：list.longcount query using joins (Linq/Lambda)list.longcount 使用连接查询 (Linq/Lambda)
【发布时间】：2014-10-22 16:22:52
【问题描述】：

我有两个类对象列表（Shifts 和Employees），我正在尝试使用它们创建一个连接。然后，我需要对符合搜索条件的结果项目进行计数。

以下是我正在使用的代码，但由于我找不到将结果作为特定“类型”传回的方法，它默认为布尔值并警告我这会导致问题：

' Count Shifts for selected hour where: started before or on this 
"hour" AND ends after or during this "hour" and Department = filter 
value
intShift = Me.Shifts.LongCount(From myshift In Me.Shifts Join 
myEmp In Me.EmployeesList On myshift.EmployeeName Equals myEmp.Name 
Where myshift.Description = "Shift" And myshift.DateStart.Hour <= 
myHour.Hour And myshift.DateEnd.Hour >= myHour.Hour _
And myshift.DateStart.Date = myDay.Date And myEmp.Department = 
strFilter _ Or myshift.Description = "Overtime" And 
myshift.DateStart.Hour <= myHour.Hour And myshift.DateEnd.Hour 
>= myHour.Hour _
And myshift.DateStart.Date = myDay.Date And myEmp.Department = 
strFilter)

没有加入员工列表和没有匹配的员工搜索过滤器的搜索工作完美，但无法将两者结合起来。

我已经搜索了 linq/lambda 和内连接示例，但我似乎找不到将这些与 longcount 函数相结合的示例。

【问题讨论】：

标签： vb.net linq join lambda

【解决方案1】：

我试图根据您的 sn-p 组合一个最小的场景。如果您直接从查询中请求Count 或LongCount，那么结果似乎与预期的一样。

    Dim Shifts() = {
        New With {.DateStart = #1/1/2014#,
                  .DateEnd = #1/2/2014#,
                  .Description = "Overtime",
                  .EmployeeName = "Darren"}
    }

    Dim EmployeesList() = {
        New With {.Name = "Darren",
                  .Department = "SO"}
        }

    Dim strFilter = "SO"
    Dim myHour = #1/1/2014#
    Dim myDay = myHour

    Dim query =
        From myshift In Shifts Join myEmp In EmployeesList _
        On myshift.EmployeeName Equals myEmp.Name _
        Where myshift.Description = "Shift" _
        And myshift.DateStart.Hour <= myHour.Hour _
        And myshift.DateEnd.Hour >= myHour.Hour _
        And myshift.DateStart.Date = myDay.Date _
        And myEmp.Department = strFilter _
        Or myshift.Description = "Overtime" _
        And myshift.DateStart.Hour <= myHour.Hour _
        And myshift.DateEnd.Hour >= myHour.Hour _
        And myshift.DateStart.Date = myDay.Date _
        And myEmp.Department = strFilter

    Console.WriteLine(query.Count)
    Console.WriteLine(query.LongCount)

【讨论】：