vb2008 insert and update record using one button - sql

Question

I am trying to make a glossary. I have a form with a listbox, 2 textboxes, and a save button.
The listbox is now populated with words from the database, and when a word is selected, its definition will display in textbox2.
The user can add a record by filling the textbox1 with a new word and textbox2 with its definition,and clicking the save button. If the new word already existed it will not allow to save a new record, also if there's a null value between the 2 textboxes. If it doesn't exist it will be inserted on the table and the new word will be added to the listbox.
The user can also update the record by selecting first a word on the list then edit the word and/or definition and clicking the save button.
I already got the updating part to work but I have problem in inserting a new record. I can't do it properly. The glossary table has only 2 fields: word, definition. Here's my code:
Dim myCmd As New MySqlCommand
Dim myReader As MySqlDataReader
Dim myAdptr As New MySqlDataAdapter
Dim myDataTable As New DataTable
Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click
Call Connect()
With Me
If Blank() = False Then
If Duplicate() = False Then
STRSQL = "insert into glossary values (#word, #def)"
myCmd.Connection = myConn
myCmd.CommandText = STRSQL
myCmd.Parameters.AddWithValue("word", txtNew.Text)
myCmd.Parameters.AddWithValue("def", txtdefine.Text)
myCmd.ExecuteNonQuery()
myCmd.Dispose()
MsgBox("Record Added")
Dim word As String
word = txtNew.Text
lstword.Items.Add(word)
'myConn.Close()
'Me.FillListbox()
Else
myConn.Open()
STRSQL = "Update glossary set word = #term, definition = #mean where word = #term"
myCmd.Connection = myConn
myCmd.CommandText = STRSQL
myCmd.Parameters.AddWithValue("term", txtNew.Text)
myCmd.Parameters.AddWithValue("mean", txtdefine.Text)
myCmd.ExecuteNonQuery()
myCmd.Dispose()
MsgBox("Record Updated", MsgBoxStyle.Information, "New word added")
End If
End If
End With
End Sub
Public Function Blank() As Boolean
Call Connect()
With Me
If .txtNew.Text = "" Or .txtdefine.Text = "" Then
Blank = True
MsgBox("Cannot save! Term and definition should not contain null value", MsgBoxStyle.Critical, "Unable to save")
Else
Blank = False
End If
End With
End Function
Public Function Duplicate() As Boolean
Call Connect()
With Me
STRSQL = "Select * from glossary where word = '" & txtNew.Text & "'"
myCmd.Connection = myConn
myCmd.CommandText = STRSQL
If myDataTable.Rows.Count <> 0 Then
Duplicate = True
'MsgBox("Word already exist. Please check the word.", MsgBoxStyle.Critical, "Duplicate.")
Else
Duplicate = False
End If
myConn.Close()
End With
End Function
this is my connection module:
Public myConnectionString As String
Public STRSQL As String
Public myConn As New MySqlConnection
Public Sub Connect()
With myConn
Try
If .State = ConnectionState.Open Then
.Close()
End If
myConnectionString = "Database=firstaidcqs;Server=localhost;Uid=root;Password="
.ConnectionString = myConnectionString
.Open()
'MsgBox("Successful Connection")
Catch ex As Exception
MsgBox(ex.Message, MsgBoxStyle.Critical, "Connection Error")
.Close()
End Try
End With
End Sub
Public Sub Disconnect()
With myConn
.Close()
.Dispose()
End With
End Sub
How can I make this work properly?

Answer 1

You are using global variables in all the code above.
myConn and myCmd
in particular, you call Dispose on myCmd but I can't see anywhere the reinitialization of the object with New. Also, forgetting for a moment the myCmd.Dispose problem, you don't reset the myCmd parameters collection. In this way you end up with a wrong Parameter collection for the command executed, Also don't forget to open the connection for the insert part. (and close it for both parts)
You could easily avoid the use of unnecessary global variables
....
If Duplicate() = False Then
STRSQL = "insert into glossary values (#word, #def)"
Using myCmd = new MySqlCommand(STRSQL, myConn)
myConn.Open()
myCmd.Parameters.AddWithValue("word", txtNew.Text)
myCmd.Parameters.AddWithValue("def", txtdefine.Text)
myCmd.ExecuteNonQuery()
End Using
myConn.Close()
.....
Else
STRSQL = "Update glossary set word = #term, definition = #mean where word = #term"
Using myCmd = new MySqlCommand(STRSQL, myConn)
myConn.Open()
myCmd.Parameters.AddWithValue("term", txtNew.Text)
myCmd.Parameters.AddWithValue("mean", txtdefine.Text)
myCmd.ExecuteNonQuery()
End Using
myConn.Close()
.....
A better solution will be changing the Connect() method to return the initialized connection instead of using a global variable. In that way you could enclose also the creation and destruction of the connection in a Using statement
Using myConn as MySqlConnection = Connect()
.......
End Using
For this to work you need to change the code of Connect in this way
Public Function Connect() as MySqlConnection
Dim myConn As MySqlConnection
myConnectionString = "Database=firstaidcqs;Server=localhost;Uid=root;Password="
myConn = New MySqlConnection(myConnectionString)
myConn.Open()
return myConn
End Sub
No need of a Disconnect function because you will always use the Using statement that will close the connection for you, no need to have a global variable to keep the connection because you will reopen the connection every time you need it and close afterward. Don't think that this is not performant because ADO.NET implements connection pooling (It is an MSDN article for SqlServer, but the concept applies also to MySql)

Answer 2

yay!! I got it working now :D (my apology, it took me a long time to finish this..i'm still learning). Here's my final code:
Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click
Call Connect()
If Blank() = False Then
If Duplicate() = False Then
STRSQL = "insert into glossary values (#word, #def)"
Using myCmd = New MySqlCommand(STRSQL, myConn)
myConn.Open()
myCmd.Parameters.AddWithValue("word", txtNew.Text)
myCmd.Parameters.AddWithValue("def", txtdefine.Text)
myCmd.ExecuteNonQuery()
End Using
myConn.Close()
MsgBox("Record Added")
Dim word As String
word = txtNew.Text
lstword.Items.Add(word)
myConn.Close()
Else
STRSQL = "Update glossary set word = #term, definition = #mean where word = #term"
Using myCmd = New MySqlCommand(STRSQL, myConn)
myConn.Open()
myCmd.Parameters.AddWithValue("term", txtNew.Text)
myCmd.Parameters.AddWithValue("mean", txtdefine.Text)
myCmd.ExecuteNonQuery()
End Using
myConn.Close()
MsgBox("Record Updated", MsgBoxStyle.Information, "New word added")
Dim str As String
str = txtNew.Text
myConn.Close()
End If
End If
End Sub
Public Function Blank() As Boolean
Call Connect()
With Me
If .txtNew.Text = "" Or .txtdefine.Text = "" Then
Blank = True
MsgBox("Cannot save! Term and definition should not contain null value", MsgBoxStyle.Critical, "Unable to save")
Else
Blank = False
End If
End With
End Function
Public Function Duplicate() As Boolean
Dim dset As New DataSet
Call Connect()
With Me
STRSQL = "Select * from glossary where word = '" & txtNew.Text & "'"
myCmd.Connection = myConn
myCmd.CommandText = STRSQL
myAdptr.SelectCommand = myCmd
myAdptr.Fill(dset, "glossary")
myDataTable = dset.Tables("glossary")
If myDataTable.Rows.Count > 0 Then
Duplicate = True
'MsgBox("Word already exist. Please check the word.", MsgBoxStyle.Critical, "Duplicate.")
Else
Duplicate = False
End If
myConn.Close()
End With
End Function
I still used the my first module but I already removed the Disconnect() function. #Steve - thank you very much for the help sir, I'll try using what you suggested to me some time..maybe on my next program. God speed!! :)