I'm having a problem when I'm reading data from a SQL Server database. The main thing is that I want to read the data from the database and display the data in a Label control. But the concern is that it can't read data to it. I will show you the code snippet and any comments/suggestions are gladly considered.
Option Explicit On
Imports System.Data
Imports System.Data.OleDb
Partial Class ViewDetail
Inherits System.Web.UI.Page
Dim con As OleDbConnection
Dim cmd As OleDbCommand
Dim dr As OleDbDataReader
Dim InstructorID As Integer
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
InstructorID = Request.QueryString("Instructor_ID")
Integer.TryParse(lblID.Text, InstructorID)
con = New OleDbConnection("Provider=SQLNCLI11;Data Source=ARIES-PC\SQLEXPRESS;Integrated Security=SSPI;Initial Catalog=SchoolDB")
con.Open()
cmd = New OleDbCommand("SelectData", con)
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.AddWithValue("#id", InstructorID)
dr = cmd.ExecuteReader
If dr.HasRows Then
While dr.Read
lblID.Text = dr("Instructor_ID").ToString
lblFirstname.Text = dr("FirstName").ToString
lblLastname.Text = dr("LastName").ToString
lblAddress.Text = dr("Address").ToString
lblContact.Text = dr("Contact_Number").ToString
End While
End If
dr.Close()
cmd.Dispose()
con.Close()
End Sub
End Class
This line seems to be totally wrong
Integer.TryParse(lblID.Text, InstructorID)
This lines takes the current value in the lblID.Text at the Page_Load event and tries to set the value of InstructorID. But your code seems to want this value from the QueryString passed that contains the real value.
If you are certain the the QueryString contains a valid integer then remove that line and add
InstructorID = Convert.ToInt32(Request.QueryString("Instructor_ID"))
Related
I'm a beginner in vb.net. Currently I'm develop a simple application by using a grid view. however, I'm facing a problem in deleting the data. When I click delete button, it keep adding the blank line. and this blank line is affected my database also. and this blank line also can't be deleted from database manually.
here my code behind
`Imports System.Data.SqlClient
Imports System.Drawing
Imports System.Data
Imports System.Configuration
Imports System.Linq
Partial Class test2
Inherits System.Web.UI.Page
Dim AMS As String = System.Web.Configuration.WebConfigurationManager.ConnectionStrings("AMS").ConnectionString
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
If Not IsPostBack Then
Me.BindData()
End If
End Sub
Private Sub BindData()
Dim dt As DataTable = New DataTable
Dim strConnString As String = ConfigurationManager.ConnectionStrings("AMS").ConnectionString
Using con As SqlConnection = New SqlConnection(strConnString)
Dim strQuery As String = "SELECT * FROM ModuleDetail"
Using cmd As SqlCommand = New SqlCommand(strQuery)
Dim sda As SqlDataAdapter = New SqlDataAdapter
cmd.Connection = con
con.Open()
sda.SelectCommand = cmd
sda.Fill(dt)
GridView1.DataSource = dt
GridView1.DataBind()
End Using
End Using
End Sub
Protected Sub GridView1_RowDeleting(ByVal sender As Object, ByVal e As GridViewDeleteEventArgs)
Dim IsDeleted As Boolean = False
Dim ModuleID As String = Convert.ToInt32(GridView1.DataKeys(e.RowIndex).Value.ToString())
Dim ModuleName As Label = CType(GridView1.Rows(e.RowIndex).FindControl("lblModuleName"), Label)
Dim SubModule As Label = CType(GridView1.Rows(e.RowIndex).FindControl("lblSubModule"), Label)
Dim strConnString As String = ConfigurationManager.ConnectionStrings("AMS").ConnectionString
Using con As SqlConnection = New SqlConnection(strConnString)
Using cmd As SqlCommand = New SqlCommand
cmd.CommandType = CommandType.Text
cmd.CommandText = "DELETE FROM ModuleDetail WHERE ModuleID=#ModuleID"
cmd.Parameters.AddWithValue("#ModuleID", ModuleID)
cmd.Connection = con
con.Open()
IsDeleted = cmd.ExecuteNonQuery() > 0
con.Close()
GridView1.DataSource = cmd
GridView1.DataBind()
End Using
End Using
If IsDeleted Then
lblMsg.Text = "'" & SubModule.Text & "' details has been deleted successfully!"
lblMsg.ForeColor = System.Drawing.Color.Green
BindData()
Else
lblMsg.Text = "Error while deleting '" & SubModule.Text & "' details"
lblMsg.ForeColor = System.Drawing.Color.Red
End If
End Sub
`
I have try a few code from others sources but it shows the same logic error which keep adding the blank line. I hope you guys can help me to solve the issue.
Though it might not relevant to your problem context, but I have observed a couple of issues from your code:
1) It seems you are binding grid twice after row delete.
2) Try commenting following lines since you already calling BindData() whithin IsDeleted flag check.
GridView1.DataSource = cmd;
GridView1.DataBind();
3) You are assigning the 'Command' object: cmd to the Grid's datasource which is not correct. Check your BindData(...) method how you need to bind Grid actually.
I'm trying to link Access database with GridView control.
Here's the question:
One successful procedure to link database query.
Protected sub Query(ByVal y as string)
Dim da As New OleDbDataAdapter(y, cn)
Dim dt As New DataTable()
da.Fill(dt)
da.Dispose()
cn.Dispose()
Me.GridView1.DataSource = dt
Me.GridView1.DataBind()
ListBox1.Visible = True
End sub
What I wanted is to re-run query if the first run returns no value/result in another procedure.
Protected Sub btnFind_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnFind.Click
x = "SELECT * From Class Where Gender ='Male' And First_name ='James' "
Query(x)
If gridview.rows.count =0 then
x= "SELECT * From Class Where Gender ='Male'"
query(x)
End If
then put result into listbox.
However, I got error of "The ConnectionString property has not been initialized." on da.Fill(dt) when running the second time. First time was successful.
OK I finally got mistake corrected. I gotta Dim cn As New OleDbConnection("Provider = Microsoft.JET.OLEDB.4.0;" & "Data Source = C:\Class.mdb") again to use query instead of once for all queries.
Create and dispose the connection in the same method
Protected Sub Query(ByVal y as string)
Dim dt As New DataTable()
Using cn as New OleDbConnection("your_connection_string"), _
da As New OleDbDataAdapter(y, cn)
da.Fill(dt)
End Using
Me.GridView1.DataSource = dt
Me.GridView1.DataBind()
End Sub
I am currently doing a project on web service for wine. I have the wine table with wineName and wineType. Also I have the search function implemented in the webservice coding as well as a separate webform to call the function of the search function
I have the following code for performing search in the search service:
<WebMethod()> _
Public Function Search(ByVal searchName As String) As System.Data.DataSet
Dim connectionString As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
Dim con As New SqlConnection(connectionString)
Dim selectSql As String = "SELECT * From Wine WHERE WineType='" & searchName + "'"
Dim selectAdapter As New Data.SqlClient.SqlDataAdapter(selectSql, con)
Dim ds As New Data.DataSet
con.Open()
selectAdapter.Fill(ds, "Wine")
con.Close()
Return ds
End Function
As for the webform, it's just a simple page with textbox labeled as searchName, a button and a gridView1 tied to ObjectDataSource.
This is the coding i have for webform:
Partial Class Search
Inherits System.Web.UI.Page
Dim searching As searchwine.Service = New searchwine.Service
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
If searchName.Text = "" Then
lblDisplayError.Text = "Can't search empty field!"
Else
Dim ds As DataSet = searching.Search(searchName.Text)
GridView1.DataSource = ds.Tables(0)
GridView1.DataBind()
GridView1.Visible = True
lblDisplayError.Visible = False
End If
End Sub
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
lblDisplayError.Text = ""
GridView1.Visible = False
End Sub
End Class
Everything seems fine, but i have the following error when i want to do a search:
System.NullReferenceException: Object reference not set to an instance of an object. at Service.Search(String searchName)
Can anyone help me out please?
I've looked through your code a couple times and I can't see what's causing the NullReferenceException. My best guess is that it couldn't find a connection string name "ConnectionString" in your web.config file, but even that doesn't quite seem to fit.
I can suggest some improvements to your search code. Hopefully you'll at least get a better error message out of this:
<WebMethod()> _
Public Function Search(ByVal searchName As String) As System.Data.DataSet
Dim ds As New Data.DataSet()
Dim connectionString As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
Using con As New SqlConnection(connectionString), _
cmd As New SqlCommand("SELECT * From Wine WHERE WineType= #SearchName", con)
'I had to guess at the exact length and type of the field here
cmd.Parameters.Add("#SearchName", SqlDbType.VarChar, 50).Value = searchName
Dim selectAdapter As New Data.SqlClient.SqlDataAdapter(cmd, con)
selectAdapter.Fill(ds, "Wine")
End Using
Return ds
End Function
But in the end I expect you'll need to step through the method and see exactly which line above throws the exception.
Looks like you are missing a New
Dim ds As DataSet = searching.Search(searchName.Text)
Should be...
Dim ds As **New** DataSet = searching.Search(searchName.Text)
I can't see why this is not working.
I have a dropdownlist named ddlRoomName and a SQL table named roomlist.
When i run the SQL command in SQL editor it works fine. But when I load the page the rooms do not load!
Am i missing something obvious here?
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Page.IsPostBack Then
ddlRoomName.Items.Clear()
ddlRoomName.Items.Add(New ListItem("--Select Room--", ""))
ddlRoomName.AppendDataBoundItems = True
Dim strConnString As String = ConfigurationManager.ConnectionStrings("a_cisco").ConnectionString
Dim strQuery As String = "Select * from roomlist"
Dim con As New SqlConnection(strConnString)
Dim cmd As New SqlCommand()
cmd.CommandType = CommandType.Text
cmd.CommandText = strQuery
cmd.Connection = con
Try
con.Open()
ddlRoomName.DataSource = cmd.ExecuteReader()
ddlRoomName.DataTextField = "RoomName"
ddlRoomName.DataValueField = "intRoom"
ddlRoomName.DataBind()
Catch ex As Exception
Throw ex
Finally
con.Close()
End Try
End If
End Sub
You are only loading them on a postback. Is it really what you want? Maybe you want:
If Not Page.IsPostBack Then
End If
(then the ViewState will keep the items in the DropDownList in a postback)
anyone can help me to connect to SQL server through vb.net using asp.net webform.. I have the database name Users and i want to use the database for the login page.. please help me..
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim ConnectionString As String
ConnectionString = ConfigurationSettings.AppSettings("ConnectionString")
Dim con As New SqlConnection(ConnectionString)
Dim cmd As New SqlCommand("Select UserId, Pwd from Users", con)
con.Open()
Dim myreader As SqlDataReader
myreader = cmd.ExecuteReader()
While myreader.Read()
If TxtUserId.Text = myreader("UserId").ToString().Trim()
AndAlso TxtPwd.Text = myreader("Pwd").ToString().Trim() Then
Session("UserId") = TxtUserId.Text
Response.Redirect("UserMyProfile.aspx")
Else
lblMsg.Visible = True
lblMsg.Text = "Inavalid UserId/Password"
End If
End While
con.Close()
End Sub
There's no shortage of tutorials on the web for this, but a good starting point is here.
EDIT: Based on your comments above, it sounds like you're not importing the Namespace you need for the ADO.NET data objects. Try adding this to the class file:
Imports System.Data.SqlClient