如何确定列中的所有值是否为空？

Question

使用LINQ to SQL，如何确定列中的所有值是否为空，以便我可以基于此触发某个操作？

我有一个程序部分可以将整个项目分配或取消分配给设计人员，或者我可以将项目分解为较小的货件并单独分配/取消分配。我有两个不同的表显示未分配的项目，另一个显示未分配的货物。如果所有货物都已单独取消分配，我需要弄清楚如何让项目显示在未分配的项目表上。

我尝试过的是......

    If Not IsNothing(dgvAssignments.SelectedItem) Then

        Dim Count As Integer
        Dim DesignerNull As Integer

        SelectedProjectID = dgvAssignments.SelectedItem.ProjectID
        SelectedShipID = dgvAssignments.SelectedItem.Id

        Count = (From Shipment In db.Shipments
                 Where Shipment.ProjectID = SelectedProjectID
                 Select Shipment.ID).Count

        For i As Integer = 0 To Count - 1
            DesignerNull = (From Shipment In db.Shipments
                            Where Shipment.ProjectID = SelectedProjectID
                            Select Shipment.DesignerID).ToList(i)

        Next
        Do Until DesignerNull <> Nothing
            Dim UpdateProjectDesigner = (From Project In db.Projects
                                         Where Project.ID = SelectedProjectID
                                         Select Project)
            For Each Project As Project In UpdateProjectDesigner
                Project.DesignerID = Nothing
            Next
        Loop
    End If