problem Object reference not set to an instance of an object.

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I want to check in my program that plot no already exist then it should display message that"Record already exist" if not then insert the record, i used procedure in lost focus event in textbox plotno.

Code:

VB

Private Sub validateplotno()
        Dim plotnumber As String = ""
        Using cnn As New SqlClient.SqlConnection("Data Source=toshiba-pc;Initial Catalog=VRINDAVAN;User ID=sa;password=zion123")
            Using cmd As SqlClient.SqlCommand = cnn.CreateCommand()

                cmd.CommandText = "SELECT 1 FROM plotmaster WHERE plotno = @plotno"
                cmd.Parameters.AddWithValue("@plotno", plotnumber)
                cnn.Open()
                Dim exists As String = cmd.ExecuteScalar().ToString()'here shows Object reference not set to an instance of an object."}

                If exists = "1" Then
                    MessageBox.Show(plotnumber & " exists already.")
                End If
            End Using
        End Using

    End Sub

Posted 19-Oct-13 2:01am

Member 10192835

Updated 19-Oct-13 2:03am

Kenneth Haugland

v2

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thatraja · Answer 1 · 2013-10-19T02:13:00

Solution 1

Replace the below line

VB

Using cmd As SqlClient.SqlCommand

with this

VB

Using cmd As New SqlClient.SqlCommand

Posted 19-Oct-13 2:13am

thatraja

Comments

Member 10192835 20-Oct-13 4:22am

Dear sir,

now i have changed the code , in this coding it's check that data is already exist, but when it's get the new data it's doesn't add the record and showing error.object reference not set to an instance of object.
the Code:-
Private Sub validateplotno()
Dim plotnumber As String = ""
Dim cnn As New SqlConnection("Data Source=toshiba-pc;Initial Catalog=VRINDAVAN;User ID=sa;password=zion123")
cnn.Open()
Dim command As New SqlClient.SqlCommand()
command.Connection = cnn
command.CommandText = "SELECT plotno FROM plotmaster WHERE plotno = " & txtplno.Text & ""
plotnumber = command.ExecuteScalar().ToString
MessageBox.Show(plotnumber & " exists already.")
txtplno.Text = ""
txtplno.Focus()
cnn.Close()
End Sub

for inserting the new data i added the following line in the code:--

Private Sub validateplotno()
Dim plotnumber As String = ""
Dim cnn As New SqlConnection("Data Source=toshiba-pc;Initial Catalog=VRINDAVAN;User ID=sa;password=zion123")
cnn.Open()
Dim command As New SqlClient.SqlCommand()
command.Connection = cnn
command.CommandText = "SELECT plotno FROM plotmaster WHERE plotno = " & txtplno.Text & ""
If plotnumber = command.ExecuteScalar().ToString Then
MessageBox.Show(plotnumber & " exists already.")
txtplno.Text = ""
txtplno.Focus()
cnn.Close()
Else
dim command As New SqlClient.SqlCommand()
command.connection=cnn
command.commandText="Select plotno from plotmaster where plotno="& txtplno.Text &""
command.parameters.Addwith Value(@plotno",plotnumber)
endSub

now when i insert the data in plotno , if the same plot no exist then it doesn't cheque and throwing the error message that duplicate key (primary) not allowed.

thatraja 22-Oct-13 5:53am

You have to check the ID exists before insert, otherwise you'll have store new id in that column

problem Object reference not set to an instance of an object.

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problem Object reference not set to an instance of an object.

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