2つの関数呼び出しが含まれています

Question

2つのイベントのいずれかにいたすべての生徒のリストを取得したいとします。ここに私の機能は、出席者のリストを取得するためにです：

Private Function AttendanceList(ByVal Mode As AttendanceListLookupMode, ByVal AttendaceTypeID As Integer, ByVal EventID As Integer, ByVal EventOccurenceDate As Date) As IEnumerable(Of Integer) 
     'Get the attendance table for specified event 
     Dim resultSet = From a In db.tblAttendances 
         Where a.tblEventOccurence.EventID = EventID _ 
          And a.tblEventOccurence.EventOccurenceDate = EventOccurenceDate 

     'Apply mode filtering 
     Select Case Mode 
      Case AttendanceListLookupMode.AttendanceTypeIs 
       resultSet = resultSet.Where(Function(x) x.tblAttendanceType.AttendanceTypeID = AttendaceTypeID) 
      Case AttendanceListLookupMode.AttendanceTypeIsNot 
       resultSet = resultSet.Where(Function(x) x.tblAttendanceType.AttendanceTypeID <> AttendaceTypeID) 
     End Select 

     'Return the student records 
     Return resultSet.Select(Function(x) x.StudentID) 
    End Function 

    Private Enum AttendanceListLookupMode 
     AttendanceTypeIs 
     AttendanceTypeIsNot 
    End Enum 

は今、私はどちらかのイベントが次のように出席したかどうかを確認するためにクエリでそれを使用したい：

'All students 
       Dim resultSet = From s In db.tblStudents 

       resultSet = resultSet.Where(Function(x) 
               AttendanceList(AttendanceListLookupMode.AttendanceTypeIsNot, 
                   CommonAttendanceTypeIDs.Absent, 
                   CommonEventIDs.Learning, 
                   ForDate).Contains(x.StudentID) 
               Or 
               AttendanceList(AttendanceListLookupMode.AttendanceTypeIsNot, 
                   CommonAttendanceTypeIDs.Absent, 
                   CommonEventIDs.Basketball, 
                   ForDate).Contains(x.StudentID) 
              End Function) 

私はこれをコンパイルしようとすると、私は

Error 1 Overload resolution failed because no accessible 'Where' can be called with these arguments: 
Extension method 'Public Function Where(predicate As System.Linq.Expressions.Expression(Of System.Func(Of tblStudent, Integer, Boolean))) As System.Linq.IQueryable(Of tblStudent)' defined in 'System.Linq.Queryable': Nested function does not have a signature that is compatible with delegate 'System.Func(Of tblStudent, Integer, Boolean)'. 
Extension method 'Public Function Where(predicate As System.Linq.Expressions.Expression(Of System.Func(Of tblStudent, Boolean))) As System.Linq.IQueryable(Of tblStudent)' defined in 'System.Linq.Queryable'. 
Extension method 'Public Function Where(predicate As System.Func(Of tblStudent, Integer, Boolean)) As System.Collections.Generic.IEnumerable(Of tblStudent)' defined in 'System.Linq.Enumerable': Nested function does not have a signature that is compatible with delegate 'System.Func(Of tblStudent, Integer, Boolean)'. 
Extension method 'Public Function Where(predicate As System.Func(Of tblStudent, Boolean)) As System.Collections.Generic.IEnumerable(Of tblStudent)' defined in 'System.Linq.Enumerable'. 

Answer 1

は、私がチェックするための便利なコンパイラを持っていませんが、複数行のラムダ構文を使用したが、裸の表現を指定しているように見えます：このエラーが発生します。コンパイラはそれを気にしません。表現ではなく、文を期待しています。次のように2つのシンタックスが異なる：

Dim singleLinelambda = Function(x) x + 1 

Dim multiLineLambda = Function(x) 
          Return x + 1 
         End Function 

代わりにこれを試してください。

resultSet = resultSet.Where(Function(x) 
    Return AttendanceList(AttendanceListLookupMode.AttendanceTypeIsNot, 
     CommonAttendanceTypeIDs.Absent, 
     CommonEventIDs.Learning, 
     ForDate).Contains(x.StudentID) Or 
     AttendanceList(AttendanceListLookupMode.AttendanceTypeIsNot, 
     CommonAttendanceTypeIDs.Absent, 
     CommonEventIDs.Basketball, 
     ForDate).Contains(x.StudentID) 
    End Function) 

個人的に、私は、パラメータを持つ別の方法に、ラムダ本体を移動させることになります。コードを読みやすくします。

Private Function MyPredicate(Mode As AttendanceListLookupMode, AttendaceTypeID As Integer, EventID1 As Integer, EventID2 As Integer, EventOccurenceDate As Date, StudentID As Integer) As Boolean 
    Return AttendanceList(Mode, 
     AttendaceTypeID, 
     EventID1, 
     EventOccurenceDate).Contains(StudentID) Or 
     AttendanceList(Mode, 
     AttendaceTypeID, 
     EventID2, 
     EventOccurenceDate).Contains(StudentID) 
End Function 

' Usage... 
resultSet = resultSet.Where(Function(x) MyPredicate(
    AttendanceListLookupMode.AttendanceTypeIsNot, 
    CommonAttendanceTypeIDs.Absent, 
    CommonEventIDs.Learning, 
    CommonEventIDs.Basketball, 
    ForDate, 
    x.StudentID))