如何从连接到数据库的组合框中删除项目并自动刷新它？

Question

我有点小麻烦。我在这里想做的是删除连接到数据库的组合框中的一个项目，删除后，它会自动刷新组合框的内容。

        Dim cons As OleDb.OleDbConnection = New OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\athan\Documents\PAGEANT.accdb")

        Using cons


            With cmd
                .Connection = cons
                .CommandText = "DELETE FROM  Judges Where Fullname = @FullName"
                .Parameters.AddWithValue("@FullName", cmbJudges.SelectedItem.ToString)
                .Connection.Open()
                .ExecuteNonQuery()
                .Connection.Close()

                MessageBox.Show("RECORD HAS BEEN DELETED", "DELETE", MessageBoxButtons.OK, MessageBoxIcon.Information)


                txtFullNameJudge.Text = Nothing
                txtContactJudge.Text = Nothing
                txtUserNameJudge.Text = Nothing
                txtPasswordJudge.Text = Nothing
                cmbJudges.Text = ""

            End With
        End Using

它正在删除一条记录，但它没有刷新组合框的内容，所以我无法删除其他数据。好像只能删除一个数据。然后我需要重新运行程序以便删除生效。

Answer 1

第一种方法代码较多，但我认为第二种方法更接近@jmcilhinney 在评论中建议的方法，可能会带来问题。我认为 DataAdapter 需要一个主键才能成为 Select 的一部分。如果 FullName 不是 Judges table 的主键，则此方法可能无效。

您可能希望使 dt（Datatable）成为表单级变量，这样您就不必从 .DataSource 属性中提取和转换它.然后它将可用于您填充组合的方法和删除法官的方法。如果这样做，请务必删除局部变量。

Private Sub FillJudgesCombo()
    Dim dt As New DataTable
    Using cn As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\athan\Documents\PAGEANT.accdb"),
            cmd As New OleDbCommand("Select FullName From Judges")
        cn.Open()
        dt.Load(cmd.ExecuteReader)
    End Using
    cmbJudges.DisplayMember = "FullName"
    cmbJudges.DataSource = dt
End Sub

Private Sub DeleteJudge1()
    'I stored this in a local variable because we are using it more tha once in this method
    Dim NameToDelete = cmbJudges.Text
    'To update the database
    Using cons As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\athan\Documents\PAGEANT.accdb"),
            cmd As New OleDbCommand("DELETE FROM  Judges Where Fullname = @FullName", cons)
        'had to guess at the datatype and field size - check your database
        'The Add method is much preferred to the .AddWithValue
        cmd.Parameters.Add("@FullName", OleDbType.VarChar, 200).Value = NameToDelete
        cons.Open()
        cmd.ExecuteNonQuery()
    End Using
    'To update the combo box by editing DataTable
    Dim dt = DirectCast(ComboBox1.DataSource, DataTable)
    'This line uses and interpolated string indicated by the $ preceding the string.
    'This allows to insearch a variable in place in the string surronded by braces.
    Dim dr = dt.Select($"FullName = {NameToDelete}")
    dr(0).Delete()
    dt.AcceptChanges()
    ResetTextBoxesAndCombo()
    MessageBox.Show("RECORD HAS BEEN DELETED", "DELETE", MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub

Private Sub ResetTextBoxesAndCombo()
    'Offloaded this because it really has nothing to do with deleting a judge.
    txtFullNameJudge.Text = Nothing
    txtContactJudge.Text = Nothing
    txtUserNameJudge.Text = Nothing
    txtPasswordJudge.Text = Nothing
    cmbJudges.SelectedIndex = -1
End Sub

Private Sub DeleteJudge2()
    Dim NameToDelete = cmdJudges.Text
    Dim dt = DirectCast(ComboBox1.DataSource, DataTable)
    'The Select method has no idea how many rows are returned
    'so it returns an array of DataRows
    Dim dr = dt.Select($"FullName = {NameToDelete}")
    'We are only interested in the first item in the array.
    'The array should only have one element.
    dr(0).Delete()
    Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\athan\Documents\PAGEANT.accdb"),
            da As New OleDbDataAdapter("Select FullName From PAGEANT", con)
        Dim cmdBuild As New OleDbCommandBuilder(da)
        da.Update(dt)
    End Using
    ResetTextBoxesAndCombo()
    MessageBox.Show("RECORD HAS BEEN DELETED", "DELETE", MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub

Answer 2

它现在像我想要的那样工作。每当我通过组合框删除数据时，它都会删除它，然后使用 FullName 字段中的值重新加载组合框。 @Mary 和@jmcilhinney 感谢所有帮助。

这是我的删除按钮的工作代码：

 Private Sub btnJudgeDelete_Click(sender As Object, e As EventArgs) Handles btnJudgeDelete.Click


        Using cons As New OleDb.OleDbConnection(conSTR)
            Using com As New OleDb.OleDbCommand("DELETE FROM Judges WHERE FullName = @FullName")
                com.Parameters.AddWithValue("@FullName", cmbJudges.Text)
                com.Connection = cons
                cons.Open()
                com.ExecuteNonQuery()

                MessageBox.Show("DATA HAS BEEN DELETED")
            End Using
        End Using


        cmbJudges.Text = ""
        txtFullNameJudge.Text = Nothing
        txtContactJudge.Text = Nothing
        txtUserNameJudge.Text = Nothing
        txtPasswordJudge.Text = Nothing
        cmbJudges.Items.Clear()

        Dim rd As OleDb.OleDbDataReader
        Using cn As New OleDb.OleDbConnection(conSTR),
            cmd As New OleDb.OleDbCommand("Select FullName From Judges", cn)
            cn.Open()
            rd = cmd.ExecuteReader
            While rd.Read
                cmbJudges.Items.Add(rd.Item(0))
            End While
            rd.Close()
        End Using



    End Sub

如何从连接到数据库的组合框中删除项目并自动刷新它？

How to delete items from combo box which is connected to database and automatically refresh it?

vb.net

combobox

visual-studio-2019