从类型dbnull到类型integer的转换无效 [英] Conversion from type dbnull to type integer is not valid
问题描述
我收到了这个错误，我不知道如何解决这个问题.....做了研究，但未能得到合适的答案.....这是我的第一篇文章...对不起我的坏语< br $>
Private Sub btnNew_Click（ByVal sender As System.Object，ByVal e As System.EventArgs）处理btnNew.Click
cnnOLEDB =新的SqlConnection（数据源= SHRAYAS-PC;初始目录= Bag_Shop;集成安全性=真）
cnnOLEDB.Open（）
来电清除（）
Dim cmd作为新的SqlCommand（从employee_details选择最大值（emp_id）， cnnOLEDB）
Dim maxrows As Integer = cmd.ExecuteScalar（）
maxrows = maxrows + 1
txt_id.Text = maxrows
'MsgBox（maxrows）
cmd =没什么
flag = 2
btnSave.Text =保存
btnNew.Enabled = Fals e />
btnDelete.Enabled = False
btnSearch.Enabled = False
btnFirst.Enabled = False
btnPrevious。 Enabled = False
btnNext.Enabled = False
btnLast.Enabled = False
End Sub
我尝试了什么：
这是我得到的异常错误详细信息： -
System.InvalidCastException未处理
消息=从类型'DBNull'转换为'Integer'类型无效。
Source = Microsoft.VisualBasic
StackTrace：
at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger（Object Value）
位于C：\ Users \ SHRAYAS \Desktop \ Bag Shop中的Bag_Shop.employee_details.btnNew_Click（Object sender，EventArgs e）中的商店\ Bag_Shop\employee_details.vb：第74行
at System.Windows.Forms.Control.OnClick（ EventArgs e）
在System.Windows.Forms.Button.OnMouseUp（MouseEventArgs mevent）
在System.Windows.Forms.Control.WmMouseUp（Message& m，MouseButtons按钮，Int32点击）
在System.Windows.Forms.Control.WndProc（消息& m）
在System.Windows.Forms.ButtonBase.WndProc（消息& m）
在System.Windows.Forms.Button.WndProc（消息& m）
在System.Windows.Forms.Control.ControlNativeWindow.WndProc（消息& m）
在System.Windows.Forms.NativeWindow.DebuggableCallback（IntPtr hWnd，Int32 msg，IntPtr wparam，IntPtr lparam）
在System.Windows.Forms.UnsafeNativeMethods。 DispatchMessageW（MSG& msg）
在System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop（Int32 dwComponentID，Int32 reason，Int32 pvLoopData）
System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner（Int32 reason，ApplicationContext context）
在System.Windows.Forms.Application.ThreadContext.RunMessageLoop（Int32 r）
在Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel（）
$中，$。
$ b at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run（String [] commandLine）
at Bag_Shop.My.MyApplication.Main（String [] Args）in 17d14f5c-a337-4978-8281- 53493378c1071.vb：第81行
at System.AppDomain._nExecuteAssembly（Assembly assembly，String [] args）
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly（）<在System.Threading.ExecutionContext.Run上执行
（ExecutionContext executionContext，ContextCallback回调，对象状态）
at System.Threading.ThreadHelper.ThreadStart（）
InnerException：
i got this error and i don't know how to solve this.....did research but failed to get an appropriate answer.....this is my first post...sorry for my bad language
Private Sub btnNew_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNew.Click
cnnOLEDB = New SqlConnection("Data Source=SHRAYAS-PC; Initial Catalog=Bag_Shop; Integrated Security=True")
cnnOLEDB.Open()
Call clear()
Dim cmd As New SqlCommand("Select Max(emp_id) from employee_details", cnnOLEDB)
Dim maxrows As Integer = cmd.ExecuteScalar()
maxrows = maxrows + 1
txt_id.Text = maxrows
'MsgBox(maxrows)
cmd = Nothing
flag = 2
btnSave.Text = "Save"
btnNew.Enabled = False
btnDelete.Enabled = False
btnSearch.Enabled = False
btnFirst.Enabled = False
btnPrevious.Enabled = False
btnNext.Enabled = False
btnLast.Enabled = False
End Sub
What I have tried:
this the exception error details which i am getting :-
System.InvalidCastException was unhandled
Message=Conversion from type 'DBNull' to type 'Integer' is not valid.
Source=Microsoft.VisualBasic
StackTrace:
at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(Object Value)
at Bag_Shop.employee_details.btnNew_Click(Object sender, EventArgs e) in C:\Users\SHRAYAS\Desktop\Bag Shop\Bag_Shop\employee_details.vb:line 74
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
at Bag_Shop.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
InnerException:
推荐答案
问题是你的tabl中没有记录的时候e
The problem is that the when there are no records in your table the result of the
cmd.ExecuteScalar()的结果是 DbNull 。哪个是班级。并且你试图把它推到一个整数。
所以我的建议是首先把它的结果变成一个隐式类型的变量（比如C＃中的var，不确定VB）然后检查它的 DbNull ，将0推到整数值，否则是实际值。
备用解决方案：使用Ashish建议的解决方案，并在查询中放置一个ISNULL。
is DbNull. Which is a class. And you are trying to push it to an integer.
So my suggestion would be to first take the result of this into an implicitly typed variable(like var in C#, not sure about VB) and then check if its DbNull, push 0 to the Integer value else the actual value.
Alternate solution: Use the solution which Ashish suggested and put an ISNULL in your query itself.
由于没有记录，您将收到此消息你的桌子（employee_details）
所以你可以做一件事在你的查询中使用Isnull功能这样
从employee_details中选择ISNULL（Max（emp_id），0）
第一条记录将返回0。
Ashish
This message you are getting due to there is no records in your table("employee_details")
so you can do one thing use Isnull function in your query like this
Select ISNULL(Max(emp_id),0) from employee_details
It will return 0 for first record.
Ashish
这篇关于从类型dbnull到类型integer的转换无效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
