主题：关于高效的流水帐设计，如果计算时考虑到到有未加载的数据时，应该如何处理？

         关于高效的流水帐设计，如果计算时考虑到到有未加载的数据时，应该如何处理？

         我用如下这样的代码，发现不行，请问应该要如何做才可以呢？求大家帮忙看看。

            Dim dr1 As DataRow
            Dim mr As DataRow = e.DataRow
            Dim drs As List(of DataRow)
           
            If mr.IsNull("盘点数") = False Then
                mr("物料需求结存数量") = mr("盘点数")+ mr("物料进货数量") - mr("物料需求数量")
                dr1 = mr
            Else
                dr1 = e.DataTable.SQLFind("[_SortKey] < " & mr("_SortKey") & " And [材料编码] = '" & mr("材料编码") & "'", "[_SortKey] Desc")
               
                If dr1 Is Nothing Then
                    mr("物料需求结存数量") = mr("物料进货数量") - mr("物料需求数量")
                    dr1 = mr
                   
                End If
            End If
            drs = e.DataTable.SQLSelect("[_SortKey] >= " & dr1("_SortKey") & " And [材料编码] = '" & dr1("材料编码") & "'", "[_SortKey]")
            For i As Integer = 1 To drs.Count - 1
                drs(i)("物料需求结存数量") = drs(i-1)("物料需求结存数量") + drs(i)("物料进货数量") - drs(i)("物料需求数量")
            Next
            e.DataTable.SQLUpdate(drs)
            e.DataTable.Load
           
            If e.DataCol.Name = "材料编码" AndAlso e.OldValue IsNot Nothing AndAlso e.OldValue <> e.NewValue Then
                dr1 = e.DataTable.SQLFind("[_SortKey] < " & mr("_SortKey") & " And [材料编码] = '" & e.OldValue & "'", "[_SortKey] Desc")
                If dr1 Is Nothing Then
                    dr1 = e.DataTable.SQLFind("[材料编码] = '" & e.OldValue & "'", "[_SortKey]")
                    If dr1 IsNot Nothing And dr1.IsNull("盘点数") = False Then
                        dr1("物料需求结存数量") = dr1("盘点数") + dr1("物料进货数量") - dr1("物料需求数量")
                    ElseIf dr1 IsNot Nothing And dr1.IsNull("盘点数") = True Then
                        dr1("物料需求结存数量") = dr1("物料进货数量") - dr1("物料需求数量")
                    End If
                End If
               
                If dr1 IsNot Nothing Then
                    drs = e.DataTable.SQLSelect("[_SortKey] >= " & dr1("_SortKey") & " And [材料编码] = '" & dr1("材料编码") & "'", "[_SortKey]")
                    For i As Integer = 1 To drs.Count - 1
                        drs(i)("物料需求结存数量") = drs(i-1)("物料需求结存数量") + drs(i)("物料进货数量") - drs(i)("物料需求数量")
                    Next
                    e.DataTable.SQLUpdate(drs)
                    e.DataTable.Load
                   
                End If
            End If