How to display data from mysql base from Dropdownlist selection - mysql

Question

i want to display mysql data base from the dropdownlist. i populate data from dropdownlist using this code and it works perfectly. in this code it will show the productnames in the dropdownlist
If Not Me.IsPostBack Then
Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
Using con As New MySqlConnection(constr)
Using cmd As New MySqlCommand("SELECT tbl_productid,tbl_productname FROM tbl_products")
cmd.CommandType = CommandType.Text
cmd.Connection = con
con.Open()
cmbProducts.DataSource = cmd.ExecuteReader()
cmbProducts.DataTextField = "tbl_productname"
cmbProducts.DataValueField = "tbl_productid"
cmbProducts.DataBind()
con.Close()
End Using
End Using
cmbProducts.Items.Insert(0, New ListItem("Select Product"))
End If
Now base from the selected product name i want to display its productID to textbox. but this code gives me no output? i dont know what is wrong with my code anyone who can help me
This is code
Protected Sub cmbProducts_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs) Handles cmbProducts.SelectedIndexChanged
'MsgBox("Hellow World!", MsgBoxStyle.Critical)
Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
Dim con As New MySqlConnection(constr)
con.Open()
Dim cmd As New MySqlCommand("SELECT tbl_productid from tbl_products where tbl_productname = '" + cmbProducts.Text + "'", con)
Dim sda As New MySqlDataAdapter(cmd)
'Dim dr As New MySqlDataReader
Dim dr As MySqlDataReader
dr = cmd.ExecuteReader
If dr.Read Then
txtProductID.Text = dr.GetValue(0)
End If
con.Close()
con.Dispose()
End Sub

Answer 1

Ok, a few things.
The drop list has two columns. data value (id), and data text.
What you have looks good.
However, when you get/grab/use the drop list, then you have this:
DropDownList1.Text - this will return the data value (1st column)
DropDownList1.SelectedValue - this will ALSO return data value (1st column)
DropDownList1.SelectedItem.Text - this gets the 2nd display text value (2nd column)
So, because a LOT of drop lists can be only one column, then the .text and .SelectedValue can both be used. (in other words, you can use .text, but it gets the first value, and since a lot of drop lists might only have one column, then .text always gets that first value). But I would consider the habit of SelectedValue for the column that drives the drop list.
In your case, you really do want the 2nd column, and thus you want to use:
DropDownList1.SelectedItem.Text
So,
New MySqlCommand("SELECT tbl_productid from tbl_products where tbl_productname = '"
+ cmbProducts.SelectedItem.Text + "'", con)

Answer 2

I used my own data to demonstrate. Also I used given control names in my test program. This is not what your want to do in your application. Your control names are good.
I broke the code into the data access part and the user interface code. There is very little code in the actual event procedure.
You have set the .DataValueField to the id so you can retrieve that value in the SelectedIndexChanged event.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
If Not IsPostBack Then
FillDropDownList()
End If
End Sub
Private Sub FillDropDownList()
Dim dt = GetListBoxData()
DropDownList1.DataTextField = "Name"
DropDownList1.DataValueField = "ID"
DropDownList1.DataSource = dt
DropDownList1.DataBind()
End Sub
Private Function GetListBoxData() As DataTable
Dim dt = New DataTable
Dim Query = "Select Top 10 ID, Name
FROM Coffees;"
Using cn As New SqlConnection(ConStr),
cmd As New SqlCommand(Query, cn)
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
Return dt
End Function
Protected Sub DropDownList1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownList1.SelectedIndexChanged
TextBox1.Text = DropDownList1.SelectedValue
End Sub
There is no need to make a second round trip to the database. You already have the data you require.