How to link to a relational database - visual basic - sql

Question

I am creating a flashcard application where each user can create flashcards which will be specific to them. I was wondering how I can link each flashcard they create to their specific account.
Imports System.Data.OleDb
Public Class CreateFlashcards
Dim pro As String
Dim connstring As String
Dim command As String
Dim myconnection As OleDbConnection = New OleDbConnection
Private Sub btnCreateFlashcard_Click(sender As Object, e As EventArgs) Handles btnCreateFlashcard.Click
pro = "provider=microsoft.ACE.OLEDB.12.0;Data Source=flashcard login.accdb"
connstring = pro
myconnection.ConnectionString = connstring
myconnection.Open()
command = " insert into Flashcards ([Front],[Back]) values ('" & txtFront.Text & "','" & txtBack.Text & "')"
Dim cmd As OleDbCommand = New OleDbCommand(command, myconnection)
cmd.Parameters.Add(New OleDbParameter("username", CType(txtFront.Text, String)))
cmd.Parameters.Add(New OleDbParameter("password", CType(txtBack.Text, String)))
MsgBox("You have successfully added the flashcard into your deck!")
Try
cmd.ExecuteNonQuery()
cmd.Dispose()
myconnection.Close()
txtFront.Clear()
txtBack.Clear()
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
End Class
This works in that it adds the data into the access database but it does not link to the users account. I have also linked the tables in access
The login table
The flashcard table
As you can see the loginID key does not link

Answer 1

Normally, the connection string for Access contains the the path to the database file for the Data Source attribute.
You will need to add a field to your Flashcard table to hold the UserID. This will tie the 2 tables together.
Database objects like connections and commands need to be disposed as well as closed. Using...End Using blocks handle this for you even if have an error. In this code you both the connection and the command are included in the same Using block.
You can pass the connection string directly to the constructor of the connection. Likewise, pass the sql command text and the connection to the constructor of the command.
When you are using parameters, which you should in Access and Sql Service, put the name of the parameter in the sql command text. It is not necessary to convert the Text property of a TextBox to a string. It is already a String.
I had to guess at the OleDbType for the parameters. Check your database. It is important to note that the order that parameters appear in the sql command text must match the order that they are added to the parameters collection. Access does not consider the name of the parameter, only the position.
I assume you can retrieve the user's ID when they log in to create flash cards. When the user logs in to use there flash cards you would do something like Select * From Flashcards Where LoginID = #UserID;.
Private Sub btnCreateFlashcard_Click(sender As Object, e As EventArgs) Handles btnCreateFlashcard.Click
Try
InsertFlashcard()
MsgBox("You have successfully added the flashcard into your deck!")
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
Private Sub InsertFlashcard()
Dim pro = "provider=microsoft.ACE.OLEDB.12.0;Data Source=Path to login.accdb"
Dim Command = " insert into Flashcards (LoginID, [Front],[Back]) values (#Id, #Front, #Back);"
Using myconnection As New OleDbConnection(pro),
cmd As New OleDbCommand(Command, myconnection)
cmd.Parameters.Add("#UserID", OleDbType.Integer).Value = ID
cmd.Parameters.Add("#Front", OleDbType.VarChar).Value = txtFront.Text
cmd.Parameters.Add("#Back", OleDbType.VarChar).Value = txtBack.Text
myconnection.Open()
cmd.ExecuteNonQuery()
End Using
End Sub
EDIT
As per comment by ADyson I have added code to retrieve ID. Of course in your real application you would be salting and hashing the password. Passwords should never be stored as plain text.
Private ID As Integer
Private Sub btnLogIn_Click(sender As Object, e As EventArgs) Handles btnLogIn.Click
Dim pro = "provider=microsoft.ACE.OLEDB.12.0;Data Source=Path to login.accdb"
Using cn As New OleDbConnection(pro),
cmd As New OleDbCommand("Select LoginID From login Where Username = #Username and Password = #Password;")
cmd.Parameters.Add("#Username", OleDbType.VarChar).Value = txtUserName.Text
cmd.Parameters.Add("#Password", OleDbType.VarChar).Value = txtPassword.Text
cn.Open()
Dim result = cmd.ExecuteScalar
If Not result Is Nothing Then
ID = CInt(result)
Else
MessageBox.Show("Invalid Login")
End If
End Using
End Sub