Exception: must declare the variable '@uname'

[krisssgopi]

Hi Team,
Thanks for your effort. When am trying to execute below code it was throwing an exception must declare the variable @uname. Please trigger me where it was going wrong. thanks in advance.
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Try
            con.Open()
            param = New SqlParameter()
            param.ParameterName = "@uname"
            param.Value = TextBox1.Text
            cmd.CommandType = CommandType.Text
            cmd.CommandText = "select * from student where fname=@uname"
            cmd.Parameters.Add(param)
            da = New SqlDataAdapter(cmd.CommandText, con)
            da.Fill(ds)
            DataGridView1.DataSource = ds.Tables(0)
        Catch ex As Exception
            MsgBox(ex.Message.ToString)
        End Try

[balabaster]

The problem is where you're assigning the data adapter. You're providing the command text and not the command:

da = New SqlDataAdapter(cmd.CommandText, con)

equates to the same thing as:

da = New SqlDataAdapter("select * from student where fname=@uname", con)

What you actually need is to new it up using the command object you've painstakingly built and attached your parameter to:

da = New SqlDataAdapter(cmd, con)

Hope that helps...

Side note: When you've got an existing command you want to attach a parameter to, it's a better practice to use:

Dim cmd = con.CreateCommand()
Dim param = cmd.CreateParameter()

as opposed to:

Dim cmd = new SqlCommand()
Dim param = new SqlParameter()

This way if you ever need to modify the type of database connection you're using, you only need to change the connection type - the rest will follow without having to modify tons of code. In fact, where at all possible, the type of connection should even be configurable through a configuration file and should automatically determine the it's type - but that's another topic for another day...

[krisssgopi]

@balabaster
Hi team,

i modified the code as per your instruction. But it was throwing the same error.
how shall i declare the sql parameter. Please help me.

Try
            con.Open()
            param = New SqlParameter()
            param.ParameterName = "@uname"
            param.Value = "TextBox1.Text"
            cmd.Parameters.Add(param)
            cmd = New SqlCommand("select * from Student where fname=@uname", con)
            'cmd.CommandText = "select * from student where fname=@uname"
            da = New SqlDataAdapter(cmd)
            da.Fill(ds)
            DataGridView1.DataSource = ds.Tables(0)
        Catch ex As Exception
            MsgBox(ex.Message.ToString)
        End Try

[krisssgopi]

@krisssgopi
i modified the code as per your instruction. But it was throwing the same error.
how shall i declare the sql parameter. Please help me.

ry
            con.Open()
            param = New SqlParameter()
            param.ParameterName = "@uname"
            param.Value = "TextBox1.Text"
            cmd.Parameters.Add(param)
            cmd = New SqlCommand("select * from Student where fname=@uname", con)
            'cmd.CommandText = "select * from student where fname=@uname"
            da = New SqlDataAdapter(cmd)
            da.Fill(ds)
            DataGridView1.DataSource = ds.Tables(0)
        Catch ex As Exception
            MsgBox(ex.Message.ToString)
        End Try