How to Add an error message box for duplicate id? - mysql

Question

this is my code that inputs a record for my database. if I put a duplicate it will just terminate the program. my goal is to put a message box that displays an error so that the program will not terminate.
Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
MysqlConn = New MySqlConnection("server=localhost; user=root; pwd=; database=payrollmanagement")
MysqlConn.Open()
command = New MySqlCommand("INSERT INTO emp_info(empID,lastname,firstname,MiddleInitial,Age,address,Position,ContactNumber,pay_type,gender,dept,email) Values ('" & TextBox1.Text & "','" & TextBox5.Text & "','" & TextBox6.Text & "','" & TextBox7.Text & "','" & TextBox11.Text & "','" & TextBox3.Text & "','" & TextBox10.Text & "','" & TextBox4.Text & "','" & TextBox8.Text & "','" & TextBox10.Text & "','" & TextBox2.Text & "','" & TextBox14.Text & "')", MysqlConn)
If (TextBox1.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox2.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox3.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox4.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox5.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox6.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox7.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox8.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox9.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox10.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox11.Text = "") Then
MessageBox.Show("Data not Inserted")
ElseIf (TextBox14.Text = "") Then
MessageBox.Show("Data not Inserted")
Else
command.ExecuteNonQuery()
MessageBox.Show("Data Inserted")
Shadows_load()
End If
End Sub

Answer 1

Add a MySqlDataReader class so that the program can read if there is any existing data in the database
MysqlConn = New MySqlConnection("//YourConnection")
MysqlConn.Open()
command = New MySqlCommand("//Your sql")
MySqlDataReader reader;
reader = command.ExecuteReader()
If reader.Read() = true Then 'This will solve your problem
MessageBox.Show("There is already existing data.")
Else
If (TextBox1.Text = "") Then
MessageBox.Show("Data not Inserted")
...
Else
command.ExecuteNonQuery()
MessageBox.Show("Data Inserted")
Shadows_load()
End If
End If

Answer 2

If all textboxes are used to insert data, you can loop through textboxes to add error message boxes.
For Each c As Control In Controls
If TypeOf c Is TextBox Then
If c.Text = "" Then
MessageBox.Show("Data not Inserted")
End If
End If
Next
You can also use 'Tag' or 'TabIndex' property to identify each textbox.

Answer 3

First the validation code is run and if it is OK then attempt to insert the new user. The Insert statement will only add the user if the id does not exist.
Private Function ValidateInput() As Boolean
For Each tb In Controls.OfType(Of TextBox)
If tb.Text = "" Then
MessageBox.Show("Data not Inserted")
tb.Focus()
Return False
End If
Next
Return True
End Function
Private Function InsertUser(id As String, lname As String, fname As String, middle As String) As Integer
Dim sql = "INSERT INTO dbusers (empID, lastname, firstname, MiddleInitial)
Select #ID, #LName, #FName #MiddleIn
WHERE Not EXISTS
(SELECT * FROM dbusers WHERE empID = #ID);"
Dim RetVal As Integer
Using cn As New MySqlConnection("server=localhost; user=root; pwd=; database=payrollmanagement"),
cmd As New MySqlCommand(sql, cn)
With cmd.Parameters
.Add("#Id", MySqlDbType.VarChar).Value = id
.Add("#LName", MySqlDbType.VarChar).Value = lname
.Add("#FName", MySqlDbType.VarChar).Value = fname
.Add("#MiddleInitial", MySqlDbType.VarChar).Value = middle
End With
cn.Open()
RetVal = cmd.ExecuteNonQuery()
End Using
Return RetVal
End Function
Private Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click
If ValidateInput() Then
Dim RowsEffected = InsertUser(TextBox1.Text, TextBox2.Text, TextBox3.Text, TextBox4.Text)
If RowsEffected = 1 Then
MessageBox.Show("Successful insert.")
Else
MessageBox.Show("Error with insert.")
End If
End If
End Sub