vb.net中的sql connetion错误消息值不能为null [英] sql connetion in vb.net error message values can't null

问题描述

表名称:Adminlogin

用户名密码
拉维123
拉梅什456

表格定义:

列名称数据类型

用户名varchar(25)null
密码nvarchar(25)null

我的源代码:

Table Name: Adminlogin

Username Password
Ravi 123
Ramesh 456

Table Definition:

column name Datatype

Username varchar(25) null
Password nvarchar(25)null

My source code:

<pre lang="vb">
Dim con As New SqlConnection("Data Source=D729Z\SQLEXPRESS;Initial Catalog=Franchise;Integrated Security=True")
   Dim da As New SqlDataAdapter
   Dim ds As New SqlDataSource
   Dim cmd As New SqlCommand
   Dim dr As SqlDataReader
   Dim dt As DataTable
   Dim str As String

  str = "select * from Adminlogin where Username='"& UnameTextBox.Text &"',            ' " & UPassword.Text & " ' "

       da = New SqlDataAdapter(str, con)
       cmd = New SqlCommand(str, con)
       da.Fill(dt)
       If dt.Rows.Count < > 0 Then
           Response.Redirect("SelectBranch.aspx")
       Else
           MsgBox(" Username and password invalided ")
       End If
       cmd.ExecuteNonQuery()

       con.Close()</pre>

运行时错误消息:

da.fill(dt)是错误点
值不能为null；参数名称:dataTable



我如何解决此问题，请发送相关示例作为相关教程

Run time Error message:

da.fill(dt) is Error point
Value can''t be null; Parameter name:dataTable



how can i solve this problem, send related examples are related tutorials

推荐答案

它抱怨，因为您传递给Fill方法的参数是不是DataTable的实例.
尝试更改此行:

Its is complaining because the parameter you pass to the Fill method is not an instance of a DataTable.
Try changing this line:

Dim dt As DataTable

对此:

Dim dt As New DataTable()

还需要删除代码的以下部分，因为它们什么都不做

Also the following parts of your code need to be removed as they are doing nothing

cmd = New SqlCommand(str, con)
'
'do other stuff
'
cmd.ExecuteNonQuery()

ExecuteNonQuery用于要执行不返回结果集但返回受影响的行数"的查询integer

进一步阅读 SqlCommand.ExecuteNonQuery方法 [ ^ ]

ExecuteNonQuery is used when you want to execute a query that doesn''t return a result set, but rather returns a "number of rows" affected integer

Further reading SqlCommand.ExecuteNonQuery Method[^]

您的sql语句不好，请将其更改为:

Your sql statement is not good, please change it to:

str = "select * from Adminlogin where Username='"& UnameTextBox.Text &"' AND Password= ' " & UPassword.Text & " ' "

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