LINQ语句不更新数据库？

Question

我有以下代码：

        Dim dbHousing As New dcHousingDataContext
    Dim pullresidents = From p In dbHousing.webResidents _
                Select p.dorm_building, p.dorm_room, p.occupantnum _
                Order By dorm_building, dorm_room
    Dim j as integer = 1
    Dim previous As String = ""
    For Each row In pullresidents
        If previous = "" Then
            Dim wResident As New webResident
            wResident.occupantnum = j
            dbHousing.SubmitChanges()
            j = j + 1
            previous = row.dorm_building & " " & row.dorm_room
        Else
            If previous = row.dorm_building & " " & row.dorm_room Then
                Dim wResident As New webResident
                wResident.occupantnum = j
                dbHousing.SubmitChanges()
                j = j + 1
            Else
                Dim wResident As New webResident
                j = 1
                wResident.occupantnum = j
                dbHousing.SubmitChanges()
                j = j + 1
                previous = row.dorm_building & " " & row.dorm_room
            End If
        End If

    Next

当我运行它时，查看调试器一切看起来都没问题但是当我检查数据库表时它应该插入 - 列值（对于occupantnum）没有改变 - 它们都是空的！

不确定这是否相关，但请注意我现在已将j更新为显式为整数。我注意到在调试时wResident.occupantnum显示为Type“Integer？” - 但这似乎没有任何区别 - 当我重新运行它仍然说类型“整数？”

Answer 1

使用For Each row In pullresidents迭代所有提取的对象，但永远不会修改row。因此，没有可以发送回数据库的更改。

Answer 2

我认为你在这里做得太多了。

你只想改变行，对吗？

尝试制作：

Dim wResident As New webResident 
wResident.occupantnum = j 
dbHousing.SubmitChanges() 
j = j + 1 

进入这个：

row.occupantnum = j 
dbHousing.SubmitChanges() 
j = j + 1

Answer 3

如果这是错误的，请原谅我 - 但是如果你要保存它们，你不必将新创建的“webResident”对象与上下文相关联吗？我看不出dbHousing.SubmitChanges（）如何保存它不知道的webResidents。

Answer 4

Dave，在提交更改之前，您需要先将新的webResident对象插入到表中。

dbHousing.webResidents.InsertOnSubmit（webResident）;