具有Dynamic Where子句的Linq動態錯誤

我有四個下拉列表，用於過濾/排序gridview。

如果前3個下拉列表中的任何一個具有非0的選定值，則WhereFlag設置為True。第四個下拉列表用於指示網格排序的依據。

我的數據綁定網格視圖代碼使用System.Linq.Dynamic，如下所示...

Dim dc As New DiaryDataContext

    If WhereFlag = False Then
        'This section works...

        Dim AList = dc.D_AreaSubAreas _
                    .OrderBy(ddl_SortBy.SelectedValue)

        Dim dl As List(Of D_AreaSubArea)
        dl = AList.ToList

        dl.Insert(0, New D_AreaSubArea With {.Ref = 0,
                                            .Area = "",
                                            .SubArea = "",
                                            .Allocation = "Allocation...",
                                            .Redundant = False})

        gv_AreaSubArea.DataSource = dl
        gv_AreaSubArea.DataBind()      
        'Gridview successfully binds
        'If ddl_SortBy value is changed... Gridview binds OK.
    Else
        'This section gives error...

        Dim WhereBuild As New StringBuilder

        If ddl_AreaFilter.SelectedIndex <> 0 Then
            WhereBuild.Append("Area = '" & ddl_AreaFilter.SelectedValue & "'")
            AndFlag = True
            End If

        If ddl_SubAreaFilter.SelectedIndex <> 0 Then
            If AndFlag = True Then
                WhereBuild.Append(" AND ")
                End If
            WhereBuild.Append("SubArea = '" & ddl_SubAreaFilter.SelectedValue & "'")
            AndFlag = True
            End If

        If ddl_AllocFilter.SelectedIndex <> 0 Then
            If AndFlag = True Then
                WhereBuild.Append(" AND ")
                End If
            WhereBuild.Append("Allocation = '" & ddl_AllocFilter.SelectedValue & "'")
        End If

        'ERROR HERE
        Dim AList = dc.D_AreaSubAreas _
                    .Where(WhereBuild.ToString) _
                    .OrderBy(ddl_SortBy.SelectedValue)
        'END ERROR

        Dim dl As List(Of D_AreaSubArea)
        dl = AList.ToList

        dl.Insert(0, New D_AreaSubArea With {.Ref = 0,
                                            .Area = "",
                                            .SubArea = "",
                                            .Allocation = "Allocation...",
                                            .Redundant = False})


        gv_AreaSubArea.DataSource = dl
        gv_AreaSubArea.DataBind()


    End If

我得到的錯誤是與動態where子句有關。我得到的錯誤是

用戶代碼未處理ParseException。字符文字必須只包含一個字符

它指向Else分支中的查詢AList。它和If分支中的查詢之間的唯一區別是添加了Where子句...，但是我無法推斷出我的代碼出了什麼問題。 AHA。