letting user type and add value to an already bound combobox - vb.net

Question

I have one combobox in my app that gets populated with a dozen or so items from SQL SERVER. I am currently trying to allow user to be able to type in a new value into the combobox and save it to a table in SQL SERVER. I'm looking for something along the lines of a DropDownStyle of DropDown and DropDownList. Basically I'm hoping to let the user type in the combobox, however if the value is not there, i want to be able to give them an option of saving it (probably on lost focus). I'm wondering what would be a good way of doing something like that.
On lost focus should I basically go through each item that is currently in the drop down and check it against the value entered?
EDIT:
Sql="SELECT IDvalue, TextName from TblReference"
Dim objconn As New SqlConnection
objconn = New SqlConnection(conn)
objconn.Open()
Dim da As New SqlDataAdapter(sql, objconn)
Dim ds As New DataSet
da.Fill(ds, "Name")
If ds.Tables("Name").Rows.Count > 0 Then
Dim dr As DataRow = ds.Tables("Name ").NewRow
ds.Tables("Name").Rows.InsertAt(dr, 0)
With c
.DataSource = ds.Tables("Name")
.ValueMember = " IDvalue "
.DisplayMember = " TextName "
End With
End If

Answer 1

You are already adding a fake/blank row to a table, you can do the same thing for a new item.
' form level datatable var
Private cboeDT As DataTable
Initializing:
cboeDT = New DataTable
Dim sql = "SELECT Id, Descr FROM TABLENAME ORDER BY Descr"
Using dbcon As New MySqlConnection(MySQLConnStr)
Using cmd As New MySqlCommand(sql, dbcon)
dbcon.Open()
cboeDT.Load(cmd.ExecuteReader())
' probably always need this even
' when there are no table rows (???)
Dim dr = cboeDT.NewRow
dr("Id") = -1 ' need a way to identify it
dr("Descr") = ""
cboeDT.Rows.InsertAt(dr, 0)
End Using
End Using
cboeDT.DefaultView.Sort = "Descr ASC"
cboE.DataSource = cboeDT
cboE.DisplayMember = "Descr"
cboE.ValueMember = "Id"
Note Users tend to have a preference as to the order of these things. The simple creatures tend to prefer alphabetical over a DB Id they may never see. To accommodate them, the DefaultView is sorted so that any new rows added will display in the correct order.
Add new items in the Leave event (much like Steve's):
Private Sub cboE_Leave(sender ...
' if it is new, there will be no value
If cboE.SelectedValue Is Nothing Then
' alternatively, search for the text:
'Dim item = cboeDT.AsEnumerable().
' FirstOrDefault(Function(q) String.Compare(q.Field(Of String)("Descr"),
' cboE.Text, True) = 0)
'If item Is Nothing Then
' ' its new...
Dim newid = AddNewItem(cboE.Text)
Dim dr = cboeDT.NewRow
dr("Id") = newid
dr("Descr") = cboE.Text
cboeDT.Rows.Add(dr)
' fiddling with the DS looses the selection,
' put it back
cboE.SelectedValue = newid
End If
End Sub
If you want to search by text:
Dim item = cboeDT.AsEnumerable().
FirstOrDefault(Function(q) String.Compare(q.Field(Of String)("Descr"),
cboE.Text, True) = 0)
If item Is Nothing Then
' its new...
...
Inserting will vary a little depending on the actual db. A key step though is to capture and return the ID of the new item since it is needed for the CBO:
Private Function AddNewItem(newItem As String) As Int32
Dim sql = "INSERT INTO MY_TABLE (Descr) VALUES (#v); SELECT LAST_INSERT_ID();"
Dim newId = -1
Using dbcon As New MySqlConnection(MySQLConnStr)
Using cmd As New MySqlCommand(sql, dbcon)
dbcon.Open()
cmd.Parameters.Add("#v", MySqlDbType.String).Value = newItem
' MySql provides it in the command object
If cmd.ExecuteNonQuery() = 1 Then
newId = Convert.ToInt32(cmd.LastInsertedId)
End If
End Using
End Using
Return newId
End Function
As noted MySql provides the LastInsertedID as a command object property. In SQL SERVER, tack ...";SELECT LAST_INSERT_ID();" to the end of your SQL and then:
newId = Convert.ToInt32(cmd.ExecuteScalar())
This is not conceptually very different from Steve's answer, except it uses the DataTable you build rather than collections which makes it (very) slightly simpler.

Answer 2

The way I do this, is on window load I perform a new SQL query to get the list of values in the table, and load them into a combobox.
Then once focus is lost, it then checks what's currently typed into the combobox against the current values already loaded. If it doesn't exist, then it's not in SQL. Something like the following...
Dim found As Boolean = False
For i As Integer = 0 To comboBox.Items.Count - 1
Dim value As String = comboBox.Items(i).ToString()
If comboBox.Text = value Then
found = True
End If
Next
If found = False Then
'the item doesn't exist.. add it to SQL
Else
'the item exists.. no need to touch SQL
End If

Answer 3

First thing I would do is to build a simple class to hold your values through a List of this class
Public Class DataItem
Public Property IDValue As Integer
Public Property TextName as String
End Class
Now, instead of building an SqlDataAdapter and fill a dataset, work with an SqlDataReader and build a List(Of DataItem)
' Class global...
Dim allItems = new List(Of DataItem)()
Sql="SELECT IDvalue, TextName from TblReference"
' Using to avoid leaks on disposable objects
Using objconn As New SqlConnection(conn)
Using cmd As New SqlCommand(Sql, objconn)
objconn.Open()
Using reader = cmd.ExecuteReader()
While reader.Read()
Dim item = new DataItem() With { .IDValue = reader.GetInt32(0), .TextName = reader.GetString(1)}
allItems.Add(item)
End While
End Using
if allItems.Count > 0 Then
allItems.Insert(0, new DataItem() With {.IDValue = -1, .TextValue = ""}
Dim bs = new BindingList(Of DataItem)(allItems)
c.DataSource = bs
c.ValueMember = "IDvalue"
c.DisplayMember = "TextName"
End If
End Using
End Using
Now the code that you want to add to your Leave event for the combobox
Sub c_Leave(sender As Object, e As EventArgs) Handles c.Leave
If Not String.IsNullOrEmpty(c.Text) Then
Dim bs = DirectCast(c.DataSource, BindingList(Of DataItem))
if bs.FirstOrDefault(Function(x) x.TextName = c.Text) Is Nothing Then
Dim item = new DataItem() With { .IDValue = -1, .TextName = c.Text}
bs.Add(item)
' here add the code to insert in the database
End If
End If
End Sub