I've been trying to use an IF/ELSE statement to query my MySQL database, but can't seem to figure out why the ELSE statement is being ignored by VB. Here's the code - any help would be appreciated:
dbConn = New MySqlConnection("Server=" & FormLogin.ComboBoxServerIP.SelectedItem & ";Port=3306;Uid=qwertyuiop;Password=lkjhgfdsa;Database=zxcvbnm")
Dim account As Boolean = True
If dbConn.State = ConnectionState.Open Then
dbConn.Close()
End If
dbConn.Open()
Dim dbQuery As String = "SELECT * FROM customer WHERE accountNumber = '" & TextBoxSearch.Text & "';"
Dim dbData As MySqlDataReader
Dim dbAdapter As New MySqlDataAdapter
Dim dbCmd As New MySqlCommand
dbCmd.CommandText = dbQuery
dbCmd.Connection = dbConn
dbAdapter.SelectCommand = dbCmd
dbData = dbCmd.ExecuteReader
While dbData.Read()
If dbData.HasRows() = True Then
MessageBox.Show("Customer Account Found!")
Else
MessageBox.Show("No Customer Records Found! Please try again!")
dbData.Close()
End If
End While
My intent is to replace the messagebox in the "IF" clause with the code that will populate my form with the data from the database.
That's because you are already reading it:
While dbData.Read()
If dbData.HasRows() = True Then
MessageBox.Show("Customer Account Found!")
Else
MessageBox.Show("No Customer Records Found! Please try again!")
dbData.Close()
End If
End While
If your reader has no records, the whole While loop will be skipped.
Try it the other way around:
If dbData.HasRows Then
While dbData.Read()
'looping through records here
End While
Else
MessageBox.Show("No Customer Records Found! Please try again!")
End If
And also the obligatory note: Don't keep your connections open and alive. Use the Using End Using bracket to automatically close your disposable objects.
I wouldn't say it's skipping your else clause, but it could be evaluating your if condition differently that you expect.
Personally, I don't like comparing anything to True. If you drop the = true, does it work?
Related
Imports MySql.Data.MySqlClient
Public Class Form1
Dim cmd As New MySqlCommand
Dim da As New MySqlDataAdapter
Dim con As MySqlConnection = JOKENCONN()
Public Function JOKENCONN() As MySqlConnection
Return New MySqlConnection("server=localhost; user id=root; password=; database =studentdb")
End Function
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
GroupBox1.Enabled = False
End Sub
Private Sub LBLLOGIN_CLICK(sender As Object, e As EventArgs) Handles lbllogin.Click
lbllogin.Text = "Login"
lbllogin.Text = "Login"
lblname.Text = "Hi, Guest"
If lbllogin.Text = "Login" Then
GroupBox1.Enabled = True
End If
End Sub
Private Sub BTNOK_CLICK(sender As Object, e As EventArgs) Handles btnok.Click
Dim Sql As String
Dim publictable As New DataTable
Try
If txtusername.Text = "" And txtpass.Text = "" Then
MsgBox("Password or username is incorrect!")
Else
Sql = "select ' from tbluseraccount where username='" & txtusername.Text & "' and userpassword='" & txtpass.Text & "'"
With cmd
.Connection = con
End With
da.SelectCommand = cmd
da.Fill(publictable)
If publictable.Rows.Count > 0 Then
Dim user_type As String
user_type = publictable.Rows(0).Item(4)
Name = publictable.Rows(0).Item(1)
If user_type = "Admin" Then
MsgBox("Welcome " & Name & "you login as Administrator")
lbllogin.Text = "logout"
lblname.Text = "Hi, " & Name
GroupBox1.Enabled = False
txtusername.Text = ""
txtpass.Text = ""
ElseIf user_type = "cetakoradi2" Then
MsgBox("Welcome " & Name & "you login as cetakoradi2")
lbllogin.Text = "logout"
lblname.Text = "Hi, " & Name
GroupBox1.Enabled = False
txtusername.Text = ""
txtpass.Text = ""
Else
End If
Else
MsgBox("contact administrator to register")
txtusername.Text = ""
txtpass.Text = ""
End If
da.Dispose()
End If
Catch ex As Exception
MsgBox(ex.Message)
con.Close()
End Try
End Sub
End Class
this the error i received
ExecuteReader CommandText property has not been properly initialized
i really need help on that. this is the error that i receives. thank you
Assuming that the name of the field represented in publictable.Rows(0).Item(4) is named user_type, then you could use the following:
'Declare the object that will be returned from the command
Dim user_type As String
'Declare the connection object
Dim con As OleDbConnection
'Wrap code in Try/Catch
Try
'Set the connection object to a new instance
con = JOKENCONN()
'Create a new instance of the command object
Using cmd As OleDbCommand = New OleDbCommand("SELECT user_type FROM tbluseraccount WHERE username=#0 AND userpassword=#1;", con)
'Paramterize the query
cmd.Parameters.AddWithValue("#0", txtusername.Text)
cmd.Parameters.AddWithValue("#1", txtpass.Text)
'Open the connection
con.Open()
'Use ExecuteScalar to return a single value
user_type = cmd.ExecuteScalar()
'Close the connection
con.Close()
End Using
Catch ex As Exception
'Display the error
Console.WriteLine(ex.Message)
Finally
'Check if the connection object was initialized
If con IsNot Nothing Then
If con.State = ConnectionState.Open Then
'Close the connection if it was left open(exception thrown)
con.Close()
End If
'Dispose of the connection object
con.Dispose()
End If
End Try
If (String.IsNullOrWhitespace(user_type)) Then
'Failed login
ElseIf (user_type = "Admin") Then
'Admin login
ElseIf (user_type = "cetakoradi2") Then
'cetakoradi2 login
Else
'Not a failed login, but also not an admin or cetakoradi2 either
End If
What this code does is setup a parameterized query to get just the user_type where the username and password match the parameterized values. Since there should only ever be one record that matches those conditions (presumably) then we're able to use ExecuteScalar to return just that single field value.
Just to reinforce the point, MySqlCommand.ExecuteScalar, just like the Microsoft counterparts, "executes the query, and returns the first column of the first row in the result set returned by the query. Extra columns or rows are ignored" and returns " The first column of the first row in the result set, or a null reference if the result set is empty ".
The proposed code by #David checks for this condition using IsNullOrWhitespace.
ExecuteScalar is effective but retrieves only one value at a time.
The other option pursued by the OP is to return a datarow, which is a valid approach if he wants to return several fields at the same time. In his example he retrieves two fields for variables user_type and Name respectively.
Be careful, VB.net like any other programming language has reserved keywords. If you do not take a habit of using good naming conventions you might one day stumble upon on one of those keywords, possibly hit obscure bugs. Name is not a good name for a variable and has the potential for confusion since every object has a name property.
To address the specific issue at hand, the error message ExecuteReader CommandText property has not been properly initialized is self-explanatory. What should have been done is simply:
With cmd
.Connection = con
.CommandText = Sql
End With
You defined a command, but did not tell it what to do. In your code variable Sql is defined but unused. With this missing bit there is a chance the code will work as expected.
Small details:
Not critical, but his condition does not work if you enter whitespace for example:
If txtusername.Text = "" And txtpass.Text = "" Then
An improvement is to simply trim the values from the textboxes:
If txtusername.Text.Trim = "" And txtpass.Text.Trim = "" Then
But I think what you want is not an And but Or. I don't think you want to allow logins without passwords.
Instead of doing multiple If/ElseIf you could have a Select Case
The sql script is validating the use of the invoice type and invoice. I need to add the check and message in the If (Me.txtMasterId.Text <> "0") method..
Protected Sub btnsubmit_Click(sender As Object, e As EventArgs) Handles btnsubmit.Click
If (Not DataForm.ValidateForm) Then
TransRepo.ModifyStatusName(gUser.CompanyId, Me.txtMasterId.Text, Me.txtStatusName.Text, chkIsPmtPlanFee.Checked, chkIsAttorneyFee.Checked, Me.cboStatus.SelectedValue, Me.txtId.Text, ParseDec(Me.txtExpenseLimit.Text), chkUserSpecPayTo.Checked)
ShowPanel(Me.pnlItemList, Me.Form)
ListOptions(Me.txtMasterId.Text)
SetPageHeader("List Status Name")
If (Me.txtId.Text = "0") Then
ShowConfirmation(Me.lblItemFrmMsg, "New name Added")
If (Me.txtMasterId.Text <> "0") Then
ShowConfirmation(Me.lblItemFrmMsg, "Status Name Saved")
Else
DataForm.DisplayError(Me.lblFrmErr)
End If
End If
End If
End Sub
Dim cn As MySqlConnection
Dim rdr As MySqlDataReader
Try
Dim Sql = "SELECT invoice_type.id
FROM invoice_type_fee
INNER JOIN invoice_name ON invoice_type.id = invoice_type_fee.`id`
WHERE invoice_name.`is_active` = 1
AND invoice_type_fee.`is_active` = 1
AND (invoice_type_fee.`fee_invoice_id` = #invoiceTyID
OR invoice_type_fee.`fee_late_invoicetype_id` = #invoiceTypeID LIMIT 1"
rdr.Read()
If (rdr.HasRows) Then
Dim message As String = "....."
Status.Visible = False
ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('" & message & "');", True)
'If (invoicetype = "1") Then
End If
Catch ex As Exception
Throw
End Try
End Sub
There is no reader. You never call ExecuteReader so there's no reader to read. You seem to think that it is Read that executes the SQL but it is not. ExecuteReader executes the SQL and then Read is used to get the data from the result set. I just realised that there isn't even a command in your case. You need to create a command to execute, execute it, then read the results
There's no point getting any data though, because all you care about is whether there is data, not what it is. That means that HasRows is all you need in that case, e.g.
Using connection As New MySqlConnection("connection string here"),
command As New MySqlCommand(sql, connection)
connection.Open()
Using reader = command.ExecuteReader()
If reader.HasRows Then
'The query produced a non-empty result set.
End If
End Using
End Using
A better option would be to add a COUNT to your SQL, call ExecuteScalar and then check whether the result is zero or not.
Dim Sql = "SELECT COUNT(invoice_type.id)
FROM invoice_type_fee
INNER JOIN invoice_name ON invoice_type.id = invoice_type_fee.`id`
WHERE invoice_name.`is_active` = 1
AND invoice_type_fee.`is_active` = 1
AND (invoice_type_fee.`fee_invoice_id` = #invoiceTyID
OR invoice_type_fee.`fee_late_invoicetype_id` = #invoiceTypeID LIMIT 1"
Using connection As New MySqlConnection("connection string here"),
command As New MySqlCommand(sql, connection)
connection.Open()
If CInt(command.ExecuteScalar()) > 0 Then
'There are matching records.
End If
End Using
i have this code,,its work (kind of).
Dim connString As String = ConfigurationManager.ConnectionStrings("connectionstring").ConnectionString
Dim conn As New SqlConnection(connString)
conn.Open()
Dim comm As New SqlCommand("SELECT username, Password,type FROM users WHERE username='" & TextBox1.Text & "' AND Password='" & TextBox2.Text & "'", conn)
Dim reader As SqlDataReader
reader = comm.ExecuteReader
Dim count As Integer
count = 0
While reader.Read
count = count + 1
End While
If count = 1 Then
MessageBox.Show("username and password are correct")
Form2.Show()
Form2.Label1.Text = Me.TextBox1.Text
Form2.Label2.Text = reader(2).ToString
ElseIf count > 1 Then
MessageBox.Show("username and password are duplicated")
Else
MessageBox.Show("username and password are wrong")
End If
im getting error with this line:
Form2.Label2.Text = reader(2).ToString
and error is "Invalid attempt to read when no data is present"
why its says "no data"
i have all data in database?
can someone help me to correct this code?
thank you ..
You should not be using a loop at all. There should be no way that you can get more than one record so what use would a loop be? You should be using an If statement and that's all:
If reader.Read() Then
'There was a match and you can get the data from reader here.
Else
'There was no match.
End If
If it's possible to have two records with the same username then there's something wrong with your database design and your app. That column should be unique and your app should be testing for an existing record when someone tries to register.
A SqlDataReader is a forward only data read element. The error is occurring because you're calling the reader's READ function twice; once as true to increment to 1, and a second time to get a false to fall out of the while statement. Since you're no longer in the WHILE statement, the reader had to have read the end of the result set, thus there is no data for you to read.
Consider the changed code below:
Dim connString As String = ConfigurationManager.ConnectionStrings("connectionstring").ConnectionString
Dim count As Integer = 0
Dim userType as string = ""
Using conn As New SqlConnection(connString)
conn.Open()
Using Comm as SqlCommand = conn.CreateCommand
comm.commandText = "SELECT username, Password, type FROM Users WHERE username = #UserName AND Password = #Pwd; "
comm.parameters.AddWithValue("#Username", TextBox1.Text)
comm.parameters.AddWithValue("#Password", Textbox2.text)
Dim reader As SqlDataReader
reader = comm.ExecuteReader
If reader IsNot Nothing Then
If reader.HasRows() Then
While reader.read
count = count + 1
If Not reader.IsDbNull(2) Then userType = reader(2).ToString
End While
End If
If Not reader.IsClosed Then reader.close
reader = Nothing
End If
End Using
End Using
If count = 1 Then
MessageBox.Show("username and password are correct")
Form2.Show()
Form2.Label1.Text = Me.TextBox1.Text
Form2.Label2.Text = userType
ElseIf count > 1 Then
MessageBox.Show("username and password are duplicated")
Else
MessageBox.Show("username and password are wrong")
End If
First off, SQLParameters are your friend. Learn them. They are the single easiest way to fight against SQL Injection when using the SqlClient classes.
Secondly, notice that I'm doing the actual retrieval of the data from the reader inside the WHILE loop. This ensures that there's actual data for me to read.
Third, notice the USING statements on the SqlConnection and SqlCommand objects. This helps with garbage collection, and has a couple of other benefits as well.
Finally, notice the checks I'm doing on the SqlDataReader before I ever attempt to access it. Things like that would prevent from another error appearing if you did not return any results.
I'm trying to pull data from ACCESS database.
As it is, the code works, and gives no errors...
However, I can't seem to be able to display a messagebox if the record doesn't exist. It simply returns an empty string.
Using dbCon = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;" & "Data Source = '" & Application.StartupPath & "\Res\T500G.accdb'")
dbCon.Open()
Dim Query1 As String = "SELECT SUM(Total) FROM [T500] WHERE Pro=#Pro"
Dim cmd1 As OleDb.OleDbCommand = New OleDbCommand(Query1, dbCon)
cmd1.Parameters.AddWithValue("#Pro", ComboBoxBP.SelectedItem.ToString)
Dim reader As OleDb.OleDbDataReader
reader = cmd1.ExecuteReader
While reader.Read()
TextBox1.Text = reader.GetValue(0).ToString
End While
reader.Close()
dbCon.Close()
End Using
I've tried using If reader.hasrows then display result in textbox, else show messagebox etc, but it doesn't work.
If reader.HasRows Then
While reader.Read()
TextBox1.Text = reader.GetValue(0).ToString
End While
Else
MessageBox.Show("asd")
End If
If I remove the .ToString from reader.GetValue(0) I get an error if the selected item from the combobox doesn't exist in the database. Cannot convert DBNull to integer or something.
So my question is, how to display a messagebox if the record "#Pro" doesn't exist?
Thanks~
Fixed(Workaround) with this
Dim ValueReturned As String
While reader.Read()
ValueReturned = reader.GetValue(0).ToString
If ValueReturned = "" Then
MessageBox.Show("Not Found", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Else
MetroTextBox1.Text = ValueReturned
End If
End While
Using OleDbDataReader is suboptimal for your query because it is never going to return a set of records to traverse:
Dim sql = "SELECT SUM(...=#p1"
' rather than sprinkling you connection string all over
' the app, you can make a function returning one
Using conn As OleDbConnection = GetConnection(),
cmd As New OleDbCommand(sql, GetConnection())
conn.Open())
' ToDo: Check that ComboBoxBP.SelectedItems.Count >0 before this
cmd.Parameters.AddWithValue("#p1", ComboBoxBP.SelectedItem.ToString)
' execute the query, get a result
Dim total = cmd.ExecuteScalar
' if there is no matches, OleDb returns DBNull
If total Is System.DBNull.Value Then
' no matches
MessageBox.Show("No matching records!"...)
Else
MessageBox.Show("The Total is: " & total.ToString()...)
End If
End Using ' disposes of the Connection and Command objects
Alteratively, you could use If IsDBNull(total) Then.... If you want, you can also convert it:
Dim total = cmd.ExecuteScalar.ToString()
' DBNull will convert to an empty string
If String.IsNullOrEmpty(total) Then
MessageBox.Show("No Soup For You!")
Else
...
End If
You could change your query to (this is for SQL-Server):
IF EXISTS (SELECT * FROM [T500] WHERE Pro = #Pro) SELECT SUM(Total) FROM [T500] WHERE Pro = #Pro ELSE SELECT 'Not Found'
And change your code to:
Dim ValueReturned As String
While reader.Read()
ValueReturned = reader.GetValue(0).ToString
End While
If ValueReturned Is Nothing OrElse ValueReturned = "Not Found" Then
MessageBox.Show("Not Found", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Else
TextBox1.Text = ValueReturned
End If
There are a lot of questions that are a duplicate of this question, but none of them seem to actually answer my specific problem.
I am writing an IRC bot, and i am adding users to a List(Of String) as you can see in the below code. However, when i want to go through a foreach loop of the users on another thread, i get the error in the title. I have even put a boolean in place to stop it from adding users, yet it still says it is being modified somehow. Any help would be greatly appreciated.
(Before you read the code, keep in mind i am new to VB.net, and even if it messy, i'd prefer to not be bashed for it as i am new)
Sub Handler()
handlerActive = True
Dim list As New List(Of String)
query = "SELECT * FROM " & channel.Substring(1)
Try
connHost.Close()
Catch
End Try
connHost.Open()
Dim cmd As MySqlCommand = New MySqlCommand(query, connHost)
Dim dataReader As MySqlDataReader = cmd.ExecuteReader()
While (dataReader.Read())
list.Add(dataReader.GetString(1))
End While
dataReader.Close()
If (users.Count > 0) Then
For Each user2 In users
Try
connHost.Close()
Catch ex As Exception
End Try
connHost.Open()
query = ("UPDATE `" & channel.Substring(1) & "` SET `Amount` = Amount + 1 WHERE `Username`='" & user2 & "'")
cmd = New MySqlCommand(query, connHost)
Try
cmd.ExecuteNonQuery()
Catch
Console.WriteLine("Failed to update user - " & user2)
End Try
Next
End If
connHost.Close()
handlerActive = False
End Sub
Below here is where i add users to my List called "users"
If (handlerActive = False And users.Contains(user) = False And user.Trim().CompareTo("") <> 0 Or user.Trim().CompareTo("jtv") <> 0 Or user.Trim().Contains(" ") = False Or user.Trim().Contains(".") = False) Then
users.Add(user)
End If