vb.net 设置数据源到组合框

Question

i want to set a data source to my combobox when i run there s no error but it keeps showing zeros in the combobox

Dim cnx As New MySqlConnection("datasource=localhost;database=bdgeststock;userid=root;password=")
        Dim cmd As MySqlCommand = cnx.CreateCommand
        Dim da As MySqlDataAdapter
        Dim ds As New DataSet
        If ConnectionState.Open Then
            cnx.Close()
        End If
        cnx.Open()
        cmd.CommandText = "SELECT idf,(prenom + ' ' + nom) AS NAME FROM fournisseur "
        da = New MySqlDataAdapter(cmd)
        cnx.Close()
        da.Fill(ds)
        da.Dispose()
        ComboBox1.DataSource = ds.Tables(0)
        ComboBox1.ValueMember = "idf"
        ComboBox1.DisplayMember = "NAME"

Answer 1

For ComboBox data source you probably don't need heavy Data Set or DataTable - collection of plain object will do the job.

Another approach would be to move representation logic to the vb.net code and leave sql server to do persistence logic only.

Public Class Fournisseur
    Public ReadOnly Property Id As Integer
    Public ReadOnly Property Name As String  

    Public Sub New(id As Integer, prenom As String, nom As String)
        Id = id
        Name = $"{pronom} {nom}".Trim()
    End Sub
End Class

You can create dedicated function to load data

Private Function LoadItems() As List(Of Fournisseur)
    Dim query = "SELECT idf, prenom, nom FROM fournisseur"

    Using connection As New MySqlConnection(connectionString)
        Using command As New MySqlCommand(query, connection)
            connection.Open()
            Dim items = new List(Of Fournisseur)()

            Using reader AS MySqlDataReader = command.ExecuteReader()
                While reader.Read()
                    Dim item As New Fournisseur(
                        reader.GetInt32(0),
                        reader.GetString(1),
                        reader.GetString(2)
                    )

                    items.Add(item)
                End While
            End Using

            Return items
        End Using
    End Using
End Function

Then usage will look pretty simple

ComboBox1.ValueMember = "Id"
ComboBox1.DisplayMember = "Name"
ComboBox1.DataSource = LoadItems()

Answer 2

I think the problem is in your sql, and mysql is performing some sort of numeric addition on prenom plus nom and producing 0

Try

CONCAT(prenom, ' ', nom) as name

In your sql instead. I prefer using concat in most RDBMS for concatenating strings because is is more consistent with its behaviour on NULLs - in sqlserver, using the concat operator of plus on something like 'a' + null results in NULL but in oracle 'a' || null 'a' || null is a - in both the CONCAT behaviour is consistent

Here's a full code with all my recommendations:

Dim cnstr = "datasource=localhost;database=bdgeststock;userid=root;password="
Dim cmd = "SELECT idf, CONCAT(prenom, ' ', nom) AS nom FROM fournisseur "
Using da As New MySqlDataAdapter(cmd, cnstr)
    Dim dt As New DataTable
    da.Fill(dt)
    ComboBox1.DataSource = dt
    ComboBox1.ValueMember = "idf"
    ComboBox1.DisplayMember = "nom"
End Using

Tips:

• you don't need to mess around with the connection: dataadapter will create/open/close it for you
• use a datatable not a dataset
• use Using
• use the constructor of MySqlDataAdapter that takes a connectionstring and a command text- shorter and nearer in this case. I only use the constructor that takes a DbConnection if I'm manually enrolling multiple commands in a transaction etc