问题描述
错误因此：从类型''DBNull''转换为''String''类型无效。
简单，对吧？好吧，没有（或者至少不适合我）。
这是一个函数，后跟下面的调用代码：
函数GetDetails（ByVal x As String，ByVal y as String）
Dim conn As New SqlConnection
（" server = localhost; uid = blah; pwd = blah; database =测试"）
Dim strSQL As String
Dim ds作为新数据集（）
strSQL =" SELECT firstv。 ocean_car，firstv.nr，firstv.equip"
strSQL& =" FROM firstv INNER JOIN"
strSQL& =" lla ON firstv.doc + firstv.po = lla.doc + lla.po"
strSQL& =" WHERE firstv.doc =" &安培; x& AND firstv.po =" &安培; y
Dim da As New SqlDataAdapter（strSQL，conn）
da.Fill（ds，" firstv"）
返回ds.Tables（" firstv"）
结束功能
来电代码：
< asp ：DataGrid runat = server id = dgDetails
DataSource =<％＃
GetDetails（container.dataitem（" doc"）），container.dat aitem（" po" ;））％>
AutoGenerateColumns = false>
< Columns>
< asp：BoundColumn DataField =" ocean_car"
HeaderText =" Carrier">< / asp：BoundColumn>
< asp：BoundColumn DataField =" nr" HeaderText =" Booking">< / asp：BoundColumn>
< asp：BoundColumn DataField =" Equip"
HeaderText =" Equip"> < / asp：BoundColumn>
< / Columns>
< / asp：DataGrid>
错误发生在第一个上面调用代码的行。
当然，我想啊，它必须从doc中取出空值并且在firstv中输入
po字段，这必须是引起"。所以我打开了Query
Analyzer并将所有空值（在每一列中）更改为空白。还是
得到了错误所以我回到QA并将它们全部更改为xyz。
仍然，我收到了错误！我想也许它与函数中的ByVal
语句有关，并切换到ByRef ...仍然没有去。任何人
有什么提示吗？
谢谢！是的，我仍然是.NET的新手。 ;）
Error is thus: "Cast from type ''DBNull'' to type ''String'' is not valid."
Simple, right? Well, no (or at least not for me).
Here''s a function, followed by the calling code below:
Function GetDetails(ByVal x As String, ByVal y as String)
Dim conn As New SqlConnection
("server=localhost;uid=blah;pwd=blah;database=test ")
Dim strSQL As String
Dim ds As New DataSet()
strSQL = "SELECT firstv.ocean_car, firstv.nr,firstv.equip "
strSQL &= "FROM firstv INNER JOIN "
strSQL &= "lla ON firstv.doc + firstv.po = lla.doc + lla.po "
strSQL &= "WHERE firstv.doc = " & x & "AND firstv.po = " & y
Dim da As New SqlDataAdapter(strSQL, conn)
da.Fill(ds, "firstv")
Return ds.Tables("firstv")
End Function
Calling code:
<asp:DataGrid runat=server id=dgDetails
DataSource=<%#
GetDetails(container.dataitem("doc"),container.dat aitem("po"))%>
AutoGenerateColumns=false>
<Columns>
<asp:BoundColumn DataField="ocean_car"
HeaderText="Carrier"></asp:BoundColumn>
<asp:BoundColumn DataField="nr" HeaderText="Booking"></asp:BoundColumn>
<asp:BoundColumn DataField="Equip"
HeaderText="Equip"></asp:BoundColumn>
</Columns>
</asp:DataGrid>
The error occurs on the very first line of the calling code above.
Naturally, I thought "ah, it must be pulling in nulls from the doc and
po fields in firstv and that must be the cause." So I opened Query
Analyzer and changed all the nulls (in every column) into blanks. Still
got the error so I went back to QA and changed them all to "xyz."
Still, I got the error!! I thought maybe it had to do with the "ByVal"
statement in the function and switched to ByRef... still no go. Anyone
have any tips, please?
Thanks! And yes, I am still am relatively new to .NET. ;)
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