having trouble updating/edit database

问题

I want to create an application where I can register person info. but I am having a problem updating/edit the data in my gridview. Below is the set of code which I've created.

Imports System.Data.SqlClient
Public Class Form1
Dim connectionString As String
Dim cnn As SqlConnection
Dim cmd As SqlCommand
Dim sql As String

below is my ADD statement and it work just fine

Private Sub btnADD_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnADD.Click

    connectionString = "Data Source=XXXX;Initial Catalog=XXXX;User ID=XXXX;Password=XXXX"
    cnn = New SqlConnection(connectionString)
    Try
        cnn.Open()
        cmd = New SqlCommand("INSERT INTO tbl_info (ID,Name) VALUES (@ID,@Name)")
        cmd.Connection = cnn
        With cmd.Parameters
            .AddWithValue("ID", txtID.Text)
            .AddWithValue("Name", txtName.Text)
        End With
        cmd.ExecuteNonQuery()
        MsgBox("has been inserted successfully")

    Catch ex As Exception
        MsgBox(ex.Message())
    End Try


    txtID.Clear()
    txtName.Clear()
End Sub

below is gridview witch is link to my database

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    'TODO: This line of code loads data into the 'TestDataSet.tbl_info' table. You can move, or remove it, as needed.
    Me.Tbl_infoTableAdapter.Fill(Me.TestDataSet.tbl_info)

End Sub

below is my update statement witch i'm having a hard time to figure what is wrong.

 Private Sub btnEdit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEdit.Click
    cnn = New SqlConnection(connectionString)
    If Not cnn.State = ConnectionState.Open Then
        cnn.Open()
    End If

    Try
        cmd = New SqlCommand("Update tble_info set Name = @Name Where ID = @ID)")
        cmd.Connection = cnn
        With cmd.Parameters
            .AddWithValue("Name", txtName.Text)
            .AddWithValue("ID", txtID.Text)
        End With
        cmd.ExecuteNonQuery()
        MsgBox("has been update successfully")
    Catch ex As Exception
        MsgBox(ex.Message())
    End Try
   End Sub
End Class

and this is the error I encountered when I execute the program

InvalidOperationExeption was unhadled
The connectionString property has not been initialize

its pointing to cnn.open()

回答1:

I'm not sure what exactly is wrong, I can only imagine that connectionStringI is somehow Null when you are trying to use it, but I think it is good practice to close the connection every time you are done using it.

So when you fetch the data instead of leaving the connection open as you do now, do something like

With New SqlConnection(connectionString)
    Try
        .Open()
        ' Do Stuff
    Catch
        ' Handle your exception
    Finally
         .Close()
    End Try
End With

That way your connection will always be closed and you won't have to worry about checking whether or not it is already open.

UPDATE

I have taken the liberty of rewriting your code the way I would do it. Can you please give this a try and see if it works for you/

You connection string property:

Private ReadOnly Property connectionString As String
    Get
        Return "Data Source=XXXX;Initial Catalog=XXXX;User ID=XXXX;Password=XXXX"
    End Get
End Property

The sub which inserts the data:

Private Sub btnADD_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnADD.Click

    Dim transaction As SqlTransaction = Nothing

    With New SqlConnection(connectionString)
        Try
            Call .Open()
            transaction = .BeginTransaction()
            With .CreateCommand()
                .Transaction = transaction
                .CommandText = "INSERT INTO [tbl_info] ([ID], [Name]) VALUES (@ID,@Name);"
                With .Parameters
                    .AddWithValue("ID", txtID.Text)
                    .AddWithValue("Name", txtName.Text)
                End With
                Call .ExecuteNonQuery()
                Call transaction.Commit()
                Call MessageBox.Show("has been inserted successfully")
            End With
        Catch ex As Exception
            Call transaction.Rollback()
            Call MessageBox.Show(ex.Message, "Error")
        Finally
            Call .Close()
        End Try
    End With

    Call txtID.Clear()
    Call txtName.Clear()

End Sub

The sub which updates the data:

Private Sub btnEdit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEdit.Click

    Dim transaction As SqlTransaction = Nothing

    With New SqlConnection(connectionString)
        Try
            Call .Open()
            transaction = .BeginTransaction()
            With .CreateCommand()
                .Transaction = transaction
                .CommandText = "UPDATE [tble_info] SET [Name]=@Name WHERE [ID]=@ID;"
                With .Parameters
                    .AddWithValue("Name", txtName.Text)
                    .AddWithValue("ID", txtID.Text)
                End With
                Call .ExecuteNonQuery()
                Call transaction.Commit()
                Call MessageBox.Show("has been update successfully")
            End With
        Catch ex As Exception
            Call transaction.Rollback()
            Call MessageBox.Show(ex.Message, "Error")
        Finally
            Call .Close()
        End Try
    End With

End Sub

If you make the connection string a (read-only) property, assuming it doesn't change, then you won't have to worry about whether it is has a value or not when you use it. Then all you have to worry about is make sure that the connection string is correct.

Note that I haven't tested this code, but it should work as is I think.

来源：https://stackoverflow.com/questions/15423898/having-trouble-updating-edit-database