I want to select some data in my table and I use this code :
Public Class frmLogin
Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOK.Click
Dim t As New DataTable
Dim adapter As OleDbDataAdapter = New OleDbDataAdapter()
Dim cmd As OleDbCommand
Dim reader As OleDbDataReader = Nothing
Dim tuser As String = txtUsername.Text
Dim sql As String = "SELECT * FROM dosen WHERE nip=tuser"
Try
cmd = New OleDbCommand(sql, conn)
reader = cmd.ExecuteReader()
While reader.Read
MessageBox.Show(reader.GetString(0).ToString & _
vbTab & vbTab & reader.GetString(1).ToString)
End While
Finally
If reader IsNot Nothing Then reader.Close()
End Try
End Sub
But there is an error in reader = cmd.ExecuteReader() line. Anyone can help me?
Correct the mistakes. The code should be
Dim reader As OleDbDataReader ' no need for nothing
Dim adapter As New OleDbDataAdapter()
Dim sql As String = "SELECT * FROM dosen WHERE nip='" & tuser & "'"
tuser is a variable, not the content
Related
I am currently writing a simple stock control Visual Basic program linked to a database.
Here's what it looks like so far.
The form displays the data in a DataGrid View and I am trying to refresh my DataGridView automatically when data is changed (using SQL) in the database I am using.
After doing some research I have found that the best way to do this is by binding the data table (using BindingSource) to the DataGridView
However I am struggling to implement this, as every implementation I have tried results in a blank DataGridView and would thoroughly appreciate it if someone could assist me.
Here's the code:
Imports System.Data.OleDb
Public Class Form1
Public connectionString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=dbStock.accdb"
Public conn As New OleDb.OleDbConnection(connectionString)
Public Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.TblStockControlTableAdapter.Fill(Me.DbStockDataSet.tblStockControl)
For i As Integer = 1 To 5
ComboBoxQty1.Items.Add(i)
ComboBoxQty2.Items.Add(i)
Next
Dim SqlQuery As String = "Select tblStockControl.[EggType] FROM tblStockControl"
Dim da As OleDbDataAdapter = New OleDbDataAdapter(SqlQuery, conn)
Dim ds As DataSet = New DataSet
da.Fill(ds, "tblStockControl")
Dim dt As DataTable = ds.Tables("tblStockControl")
'DataGridView1.DataSource = dt
For Each row As DataRow In dt.Rows
ComboBoxAdd.Items.Add(row.Item(0))
Next
For Each row As DataRow In dt.Rows
ComboBoxTake.Items.Add(row.Item(0))
Next
End Sub
Private Sub btnAddEgg_Click(sender As Object, e As EventArgs) Handles btnAddEgg.Click
conn.Open()
Dim SqlQuery As String = "Select tblStockControl.[Quantity] FROM tblStockControl WHERE EggType = '" & ComboBoxAdd.Text & "'"
Dim da As OleDbDataAdapter = New OleDbDataAdapter(SqlQuery, conn)
Dim ds As DataSet = New DataSet
da.Fill(ds, "tblStockControl")
Dim dt As DataTable = ds.Tables("tblStockControl")
Dim qty As Integer = 0
For Each row As DataRow In dt.Rows
For Each column As DataColumn In dt.Columns
qty = row(column)
Next
Next
Dim NewQty As Integer = qty + CInt(ComboBoxQty2.Text)
UpdateAddQty(NewQty)
conn.Close()
End Sub
Function UpdateAddQty(ByRef NewQty As Integer) As Integer
Dim SqlUpdate As String = "UPDATE tblStockControl SET Quantity = '" & NewQty & "' WHERE EggType = '" & ComboBoxAdd.Text & "'"
Dim SqlCommand As New OleDbCommand
With SqlCommand
.CommandText = SqlUpdate
.Connection = conn
.ExecuteNonQuery()
End With
Return (Nothing)
End Function
Private Sub btnViewStock_Click(sender As Object, e As EventArgs) Handles btnViewStock.Click
'Add code to open Access file.
End Sub
Private Sub btnTakeEgg_Click(sender As Object, e As EventArgs) Handles btnTakeEgg.Click
conn.Open()
Dim SqlQuery As String = "Select tblStockControl.[Quantity] FROM tblStockControl WHERE EggType = '" & ComboBoxTake.Text & "'"
Dim da As OleDbDataAdapter = New OleDbDataAdapter(SqlQuery, conn)
Dim ds As DataSet = New DataSet
da.Fill(ds, "tblStockControl")
Dim dt As DataTable = ds.Tables("tblStockControl")
Dim qty As Integer = 0
For Each row As DataRow In dt.Rows
For Each column As DataColumn In dt.Columns
qty = row(column)
Next
Next
Dim NewQty As Integer = CInt(ComboBoxQty1.Text) - qty
UpdateTakeQty(NewQty)
conn.Close()
End Sub
Function UpdateTakeQty(ByRef NewQty As Integer) As Integer
Dim SqlUpdate As String = "UPDATE tblStockControl SET Quantity = '" & NewQty & "' WHERE EggType = '" & ComboBoxTake.Text & "'"
Dim SqlCommand As New OleDbCommand
With SqlCommand
.CommandText = SqlUpdate
.Connection = conn
.ExecuteNonQuery()
End With
Return (Nothing)
End Function
End Class
If you are using a DataTable , then reset the dataasource of the DataGridView.I mean you need to read data from the database again. :
'Do this every time you add/Update a data
Dim da As OleDbDataAdapter = New OleDbDataAdapter(SqlQuery, conn)
Dim ds As DataSet = New DataSet
da.Fill(ds, "tblStockControl")
Dim dt As DataTable = ds.Tables("tblStockControl")
Or you can just create a row for every data you add to your database :
'Do this every time you add a data
DataGridViewRow row = (DataGridViewRow)DataGridView1.Rows[0].Clone()
row.Cells[0].Value = "Alex"
row.Cells[1].Value = "Jordan"
DataGridView1.Rows.Add(row)
Here is a code that retrieve values from the database, but my problem is that it throws out an exception saying "InvalidCastException was unhandled specified cast is not valid". I am now confused what went wrong, The code and the table stated below.
Here is the code:
Public connstring As String = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source =" & Application.StartupPath &
"\TestData.accdb; Persist Security info = false"
Public Conn As New OleDbConnection
Private Sub TestForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Loard
Conn.ConnectionString = connstring
Conn.Open()
LoadValue( )
End Sub
Private Sub LoadValue( )
Dim i As Integer
Dim cmd As OleDbCommand = New OleDbCommand
With cmd
.CommandText = "SELECT MAX(Guard_ID) FROM Guard"
.CommandType = CommandType.Text
.Connection = Conn
.ExecuteNonQuery()
Dim reader As OleDbDataReader = cmd.ExecuteReader
If reader.Read Then
TextBox1.Text = reader.GetString(0)
i = TextBox1.Text + 1
TextBox1.Text = i
reader.Close()
End If
End With
End Sub
The table reference:
Exception Error:
I am really confused now on why the code does not work, any help and advice will be gladly accepted. Thanks in advance.
try this,
Private Sub LoadValue()
Dim i As Integer
Dim cmd As OleDbCommand = New OleDbCommand
With cmd
.CommandText = "SELECT MAX(Guard_ID) FROM Guard"
.CommandType = CommandType.Text
.Connection = Conn
.ExecuteNonQuery()
Dim reader As OleDbDataReader = cmd.ExecuteReader
If reader.Read Then
Dim tmpVal As Object = reader.Item(0)
TextBox1.Text = IIf(IsDBNull(tmpVal), "0", tmpVal.ToString())
i = CInt(TextBox1.Text) + 1
TextBox1.Text = i.ToString()
reader.Close()
End If
End With
End Sub
This is my first question, by the way - and I'm not sure exactly how to ask, or say what's wrong. There's 3 things I can't sort so any help would be appreciated.
Module:
This and the first (login) form work as they are but I couldn't get either Form to reference con.connectionstring for them to use without having to re-use the string contained in "" (as they do below) - my attempts ended up with errors including saying that the state couldn't be changed as the connection was already open, but I'd like the same one string to be referenced from the Forms.
Module ConnectionModule
Public con As OleDb.OleDbConnection = New OleDb.OleDbConnection
Public da As OleDb.OleDbDataAdapter
Public ds As DataSet = New DataSet
Public Path As String = Application.StartupPath
Public Sub OpenDb()
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
con.Open()
If con.State = ConnectionState.Closed Then
MsgBox("Connection to db not made.")
End If
End Sub
Public CurrentUser As String = Nothing
End Module
The First Form:
Public Class LoginForm
Private Sub LoginForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
OpenDb()
con.Close()
End Sub
Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogin.Click
Dim ID As String = txtID.Text
Dim Pass As String = txtPassword.Text
If IsNumeric(ID) = False Or ID.Length > 4 Or Pass = Nothing Then
MsgBox("Staff ID is a 4-digit number and Password must not be blank.")
Else
Dim con As New System.Data.OleDb.OleDbConnection()
OpenDb()
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
Try
Dim sql As String = "SELECT * FROM tblStaff WHERE [StaffID]='" & ID & "' AND [Pword] = '" & Pass & "'"
Dim sqlCom As New System.Data.OleDb.OleDbCommand(sql)
'Open Database Connection
sqlCom.Connection = con
con.Open()
Dim sqlRead As System.Data.OleDb.OleDbDataReader = sqlCom.ExecuteReader()
If sqlRead.Read() Then 'Correct:
MenuForm.Show()
Me.Hide()
CurrentUser = ID
Else 'Incorrect:
MsgBox("Staff ID or Password incorrect.")
txtPassword.Text = ""
txtID.Text = ""
txtID.Focus()
End If
Catch ex As Exception
MsgBox("Database Connection Error.")
End Try
con.Close()
End If
End Sub
End Class
A form to change the password:
The problem here is that lblUser (A clarification for the user to tell them which password will be changed) only outputs the data already within the program as a variable: CurrentUser (as assigned upon successful login). No error is produced but the full name of the user isn't shown (or possibly read from the database).
I'm also unsure how the UPDATE SQL command should be contained within the second procedure, btnAccept_click, here. What the syntax is, basically. I haven't found a clear example to look at.
Imports System.Data.OleDb
Public Class PasswordForm
Private Sub PasswordForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
con = New System.Data.OleDb.OleDbConnection()
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
Dim Returned(2) As String
CurrentUser = CurrentUser
Dim cmd As OleDbCommand = New OleDbCommand("SELECT [Title], [Forename], [Surname] FROM tblStaff WHERE [StaffID]='" & CurrentUser & "'", con)
Try
con.Open()
Dim reader As OleDbDataReader = cmd.ExecuteReader()
If reader.HasRows Then
reader.Read()
'Makes db contents variables
Returned(0) = reader.Item("[Title]").ToString
Returned(1) = reader.Item("[Forename]").ToString
Returned(2) = reader.Item("[Surname]").ToString
End If
reader.Close()
Catch ex As Exception
Me.Hide()
MsgBox("Database Connection Error.")
Finally
con.Close()
End Try
lblUser.Text = "Current User: " & CurrentUser & Returned(0) & Returned(1) & Returned(2)
''Only outputs CurrentUser
End Sub
Private Sub btnAccept_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAccept.Click
Dim Current As String = txtCurrent.text
Dim NewPass As String = txtNew.Text
'Verification
If txtNew.Text = txtConfirm.Text And NewPass.Length <= 20 Then
Dim cmd As OleDbCommand = New OleDbCommand("UPDATE tblStaff SET [Pword]='" & NewPass & "' WHERE [StaffID]='" & CurrentUser & "'", con)
End If
End Sub
End Class
Thank you, again, for anyone with ideas (especially exact code).
Oh and throughout what's here there are no errors thrown. Just missing content.
you are opening the connection in openDB() and you are trying to open it again in form1, this will throw the error you are getting. So comment all the con related lines in your form. Same comment for your passowrd form also.
'Dim con As New System.Data.OleDb.OleDbConnection()
OpenDb()
'con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=F:\Computing A2\CG4 Coursework\Greener Cleaning\dbCoursework.accdb"
Try
Dim sql As String = "SELECT * FROM tblStaff WHERE [StaffID]='" & ID & "' AND [Pword] = '" & Pass & "'"
Dim sqlCom As New System.Data.OleDb.OleDbCommand(sql)
'Open Database Connection
sqlCom.Connection = con
'con.Open()
...
end try
Dim con As New SqlConnection
Dim cmd As New SqlCommand
Dim str As String
Dim dr As SqlDataReader
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
str = "select * from llr where llrno='" & TextBox1.Text & "'"
cmd = New SqlCommand(str, con)
con.Open()
dr = cmd.ExecuteReader()
If dr.HasRows Then
dr.Read()
Dim img As Byte() = DirectCast(dr("img"), Byte())
Dim ms As New MemoryStream(img)
PictureBox1.Image = Image.FromStream(ms)
End If
dr.Close()
cmd.Dispose()
con.Close()
End Sub
I think the issue may be with the previous line, try changing to this:
Dim img As Byte() = dr("img")
and see if you get the same error.
I am trying to insert a record in sql database using vb.net dataadapter, datatable, and datarow features. I use the following code but it gives me an error:
Object reference not set to an instance of an object
Imports System.Data.SqlClient
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim cn As New SqlConnection("Data Source=.\SQLEXPRESS;Initial Catalog=drpractice;Integrated Security=True")
Dim da As New SqlDataAdapter
Dim ds As New DataSet
Try
cn.Open()
da.SelectCommand = New SqlCommand("SELECT * FROM [emp_tbl]", cn)
da.Fill(ds)
Dim dt As New DataTable
dt = ds.Tables("emp_tbl")
'Error in this line(Object reference not set to an instance of an object)'
Dim dr As DataRow = dt.NewRow()
dr.Item("emp_id") = TextBox1.Text.Trim
dr.Item("emp_name") = TextBox2.Text.Trim
dr.Item("salary") = TextBox3.Text.Trim
dr.Item("age") = TextBox4.Text.Trim
dr.Item("emp_group") = TextBox5.Text.Trim
dt.Rows.Add(dr)
da.Update(ds)
MsgBox("Record Successfully Inserted")
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
End Class
check this out : Dim dr As DataRow = new dt.NewRow()
You have done everything good but change the following line:
da.Update(ds)
As following:
Dim ESCBuilder As SqlCommandBuilder = New SqlCommandBuilder(da)
ESCBuilder.GetUpdateCommand()
da.UpdateCommand = ESCBuilder.GetUpdateCommand()
da.Update(ds)
Based on the feedback here and elsewhere, the following code worked for me:
TestDataSet.GetChanges()
testTableAdapter.Fill(TestDataSet.log_test)
log_testDataGridView.Refresh()
What I needed to do was, create a new row, and go get the next value for the Primary Key(VARCHAR, NOT INT, because revisions got an "R" appended to the PK...not my rule...the rule of the company).
I wanted to put the refresh as close to the getting of the PK, which I had last after assigning values to the new datarow so it would get the latest Max +1.
So, I put the above code just before looking up the PK, and after assigning values to the datarow, other than PK. The code above caused the datarow to blank out. So, I put the above code just prior to the creation of the new DataRow.
For my code, this caused the code to get the latest data from the SQL table, then add the new datarow, and finally determine the last PK. Because the data used to populate the datarow is off my form, and there is no caclulations, the code runs fast enough for my needs. I suspect, if the connection to my database was slow, and/or, the number of people running the same process were substantial, I would have errors, such as duplicate PKs.
My answer to that would be to assign the datarow field values to variables, run the refresh, then assign the variables to the fields and save immediately.
Perhaps another way would be to get the new PK, then save an empty record, and then fill the record, except that enough of the fields in my table are REQUIRED so I might as well not try creating a blank record first.
Imports System.Data.SqlClient
Public Class Form4
Dim con As New SqlConnection
Dim cmd As New SqlCommand
Dim str As String
Dim count As Integer
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
con = New SqlConnection("server=SHREE-PC;database=Hospital;INTEGRATED SECURITY=SSPI;")
con.Open()
‘ cmd = New SqlCommand("select * from Doctor", con)
str = "insert into Doctor values('" & TextBox1.Text & "','" & TextBox2.Text & "','" & TextBox3.Text & "' )"
cmd = New SqlCommand(str, con)
count = cmd.ExecuteNonQuery()
MessageBox.Show(count & " Record inserted")
con.close()
End Sub
Imports System.Data.SqlClient
Public Class Form4
Dim con As New SqlConnection
Dim cmd As New SqlCommand
Dim str As String
Dim count As Integer
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
con = New SqlConnection("server=SHREE-PC;database=Hospital;INTEGRATED SECURITY=SSPI;")
con.Open()
cmd = New SqlCommand("select * from Patient", con)
cmd = New SqlCommand("Delete from Patient where Name ='" & TextBox1.Text & "'", con)
cmd = New SqlCommand("Delete from Patient where Address='" & TextBox2.Text & "'", con)
cmd = New SqlCommand("Delete from Patient where Dieses='" & TextBox3.Text & "'", con)
cmd = New SqlCommand("Delete from Patient where Patient_no=" & TextBox4.Text & "", con)
‘you can take any row in your program
count = cmd.ExecuteNonQuery()
MessageBox.Show("Record Deleted")
End Sub