Help! I am trying to fill a listbox with items from my database with the sql statement, I'm unsure how to fix this error as it keeps coming up. My database only contains two dates, but I need it to be expandable in future, hence the database to store dates.
Public ds As New DataSet
Public con As New OleDb.OleDbConnection 'used to connect to the database
Public provider As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
Public datafile As String = "Resources/database.accdb" 'database location and version
Public da As OleDb.OleDbDataAdapter
Public sqlstatement As String
ds.Clear()
con.ConnectionString = connString
con.Open()
sqlstatement = "SELECT ShowDate FROM AvailableDates"
da = New OleDb.OleDbDataAdapter(sqlstatement, con)
da.Fill(ds, "Dates")
lbxDates.DisplayMember = "ShowDate"
lbxDates.DataSource = ds
lbxDates.ValueMember = "ShowDate"
con.Close()
The error 'Cannot bind to the new display member' occurs on the
lbxDates.ValueMember = "ShowDate" line
You must affect the dataSource first :
lbxDates.DataSource = ds.tables("Dates")
lbxDates.DisplayMember = "ShowDate"
lbxDates.ValueMember = "ShowDate"
Related
So i have here my codes for fetching informations from the database using
the listview, and now i want to use the datagridview but i dont know how
to do it using the ADODB Connectionenter image description here.
If you are able to use an Odbc connection instead try this to retreive your data
Dim conn As New OleDb.OleDbConnection("path to your database")
Dim cmd As New OleDb.OleDbCommand
Dim da As New OleDb.OleDbDataAdapter
Dim sql as String
Sql = "your SQL Query"
conn.Open()
cmd.Connection = conn
cmd.CommandText = Sql
da.SelectCommand = cmd
You can try using Odbc Connection in VB.Net.
First add new Module named Connection.vb
Imports System.Data.Odbc
Module Connection
Public Con As New OdbcConnection
Public Adpt As New OdbcDataAdapter
Public Ds As New DataSet
Public Cmd As OdbcCommand
Public Read As OdbcDataReader
Public Sql As String
Public StrCon As String = "Dsn=Your DSN Name in Odbc Connector"
Public Sub Connect()
Con = New OdbcConnection(StrCon)
If Con.State <> ConnectionState.Closed Then Con.Close()
Con.Open()
End Sub
End Module
And next don't forget to add Imports System.Data.Odbc in every form you have to connect to your Odbc Connection.
Simple Code to add item on ComboBox from Database.
Call Connect()
Cmd = New OdbcCommand("SELECT * FROM `category` ", Con)
cmbKategori.Items.Clear()
cmbKategori.AutoCompleteCustomSource.Clear()
Read = Cmd.ExecuteReader()
If Read.HasRows = True Then
While Read.Read()
cmbKategori.AutoCompleteCustomSource.Add(Read("name_category"))
cmbKategori.Items.Add(Read("name_category"))
End While
End If
I am creating a program to book tickets for a school performance, this section of code displays dates from a database into a list box, then it gets the selected value and checks the databse with that name for the available seats.
Public ds As New DataSet 'used to store the basic elements of the database
Public con As New OleDb.OleDbConnection 'used to connect to the database
Public provider As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
Public datafile As String = "Resources/database.accdb" 'database location and version
Public da As OleDb.OleDbDataAdapter = New OleDb.OleDbDataAdapter(sqlstatement, con)
Public sqlstatement As String
Public connString As String = provider & datafile
Public UserbeingEdited As String
Public sSelectedAssetType As String
ds.Clear()
con.ConnectionString = connString
con.Open()
sqlstatement = "SELECT ShowDate FROM AvailableDates"
da.Fill(ds, "Dates")
lbxDates.ValueMember = "ShowDate"
lbxDates.DisplayMember = "ShowDate"
lbxDates.DataSource = ds.Tables("Dates")
con.Close()
Private Sub lbxDates_SelectedValueChanged(sender As Object, e As EventArgs) Handles lbxDates.SelectedValueChanged
Dim oDataRowView As DataRowView = CType(Me.lbxDates.SelectedItem, DataRowView)
lbxActs.Items.Clear()
lbxActs.Items.AddRange(IO.File.ReadAllLines("Resources/" & sSelectedAssetType & ".txt"))
sSelectedAssetType = oDataRowView("ShowDate").ToString
For Each btn As Control In Seating_Plan.Controls
If checkSeats(btn.Name()) = "True" Then
SeatCount = SeatCount + 1
End If
Next
I keep getting this error and i dont know how to fix it, please help :)
The contents of a string object cannot be changed after the object is created.
If you want to use a variable to store the SQL query creates the variable and sets its value before assigning it to OleDbDataAdapter.
Public ds As New DataSet 'used to store the basic elements of the database
Public con As New OleDb.OleDbConnection 'used to connect to the database
Public provider As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
Public datafile As String = "Resources/database.accdb" 'database location and version
Public da As OleDb.OleDbDataAdapter
Public sqlstatement As String
Public connString As String = provider & datafile
Public UserbeingEdited As String
Public sSelectedAssetType As String
ds.Clear()
con.ConnectionString = connString
con.Open()
sqlstatement = "SELECT ShowDate FROM AvailableDates"
da = new OleDb.OleDbDataAdapter(sqlstatement, con)
da.Fill(ds, "Dates")
lbxDates.ValueMember = "ShowDate"
lbxDates.DisplayMember = "ShowDate"
lbxDates.DataSource = ds.Tables("Dates")
con.Close()
This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 6 years ago.
I am trying to create a ticket system, this part of the system will display all of the acts performing on each specific day. I am also trying to show how many tickets/seats are available. I have a database with all seat locations and a boolean value to show if they are taken or not.
Public ds As New DataSet 'used to store the basic elements of the database
Public con As New OleDb.OleDbConnection 'used to connect to the database
Public provider As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
Public datafile As String = "Resources/database.accdb" 'database location and version
Public da As OleDb.OleDbDataAdapter
Public sqlstatement As String
Public connString As String = provider & datafile
lbxActs.Items.Clear()
Dim oDataRowView As DataRowView
Dim sSelectedAssetType As String
ds.Clear()
con.ConnectionString = connString
con.Open()
sqlstatement = "SELECT ShowDate FROM AvailableDates"
da = New OleDb.OleDbDataAdapter(sqlstatement, con)
da.Fill(ds, "Dates")
lbxDates.DataSource = ds.Tables("Dates")
lbxDates.DisplayMember = "ShowDate"
lbxDates.ValueMember = "ShowDate"
con.Close()
oDataRowView = CType(Me.lbxDates.SelectedItem, DataRowView)
sSelectedAssetType = oDataRowView("ShowDate").ToString
lbxActs.Items.AddRange(IO.File.ReadAllLines("Resources/" & sSelectedAssetType & ".txt"))
con.Close()
ds.Clear()
con.ConnectionString = connString
con.Open() 'Open connection to the database
sqlstatement = "SELECT * FROM [Seats" & sSelectedAssetType & "] WHERE [Available] = True "
da = New OleDb.OleDbDataAdapter(sqlstatement, con)
da.Fill(ds, "seats") 'Fill the data adapter
con.Close()
Dim recordCount, x As Short
recordCount = 0
x = 0
recordCount = ds.Tables("seats").Rows.Count
tbxLeftS.Text = recordCount
the first part of the program puts all the show dates into a list box, then depending on which one is clicked it shows a different list of acts from my text files. The second part of the program is supposed to use an SQL statement to find all the seat locations which are available. Then it counts the records and then displays the number in a text box.
Object reference not set to an instance of an object
This error appears 4 times and it highlights this line:
sSelectedAssetType = oDataRowView("ShowDate").ToString
To get rid of the error, its very likely that somehow oDataRowView is null. You need to check to make sure its not null before you try to convert it to a string. Do something like this:
IF Not isdbnull(oDataRowView)
oDataRowView = CType(Me.lbxDates.SelectedItem, DataRowView)
End if
As to why you are getting a null value for oDataRowView, that will require you to debug further. Perhaps it could be an issue with PostBack (assuming this is a web page and not winforms.
I have a DataGridView which displays the contents of a table (with sql query). But whenever I run the code, it displays this error:
No value given for one or more required parameters.
Where did it went wrong? The program ran without displaying any errors.
Here's the code for displaying in the DataGridView:
Dim connString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\BSPDatabase.accdb"
MyConn = New OleDbConnection
MyConn.ConnectionString = connString
ds = New DataSet
tables = ds.Tables
da = New OleDbDataAdapter("Select * from [Transactions] where transMonth=" & monthCombobox.Text & "", MyConn)
da.Fill(ds, "BSPDatabase") 'Change items to your database name
Dim view As New DataView(tables(0))
source1.DataSource = view
TransactionsDataGridView.DataSource = view
I think you are forming bad SQL. The value needs to be in quotes.
da = New OleDbDataAdapter(String.Format("Select * from [Transactions] where transMonth ='{0}'", monthCombobox.text), MyConn)
I have installed Oracle 10g Express Edition database on a server and install the client on my PC.
Now, I`m developing a vb.net application using visual studio 2005 and I need to use the oracle 10g express edition database. So I initialize the connection using the following connection string:
_connectionString = "User Id=Graphya;Password=Graphya;Data Source=gis64:1522/XE;"
Then I define new OracleDataAdapter, and I use the following code to fill a dataset:
Dim insertCommand As OracleCommand = New OracleCommand()
Dim commandTextTemplate As String = "INSERT INTO {0}(" & g_pfldUsername & ", " & g_pfldSubject & ") VALUES (?, ?)"
insertCommand.CommandText = String.Format(commandTextTemplate,TABLE_NAME)
insertCommand.Connection = Me.Connection
insertCommand.Parameters.Add(New Oracle.DataAccess.Client.OracleParameter(g_pfldUsername, Oracle.DataAccess.Client.OracleDbType.Varchar2, 50, g_pfldUsername))
insertCommand.Parameters.Add(New Oracle.DataAccess.Client.OracleParameter(g_pfldSubject, Oracle.DataAccess.Client.OracleDbType.Varchar2, 50, g_pfldSubject))
_OracleDataAdapter.InsertCommand = insertCommand
_OracleDataAdapter.Fill(_dataSet, TABLE_NAME)
So after debugging this code I got the following error:
Unable to cast object of type 'Oracle.DataAccess.Client.OracleCommand' to type 'System.Data.Common.DbCommand'.
#Davideg: my code is c# to fill data set
OleDbConnection cnOra = new OleDbConnection("Provider=MSDAORA;Data Source=myOracleServer;"
+ "user id=myUID;password=myPWD;"
+ "persist security info=false;");
OleDbCommand cmdPerson = new OleDbCommand
+ ("{call PackPerson.allPerson({resultset 3, ssn, fname, lname})}", cnOra);
OleDbDataAdapter daPerson = new OleDbDataAdapter(cmdPerson);
cnOra.Open();
DataSet ds = new DataSet();
daPerson.Fill(ds,"Person");
this.dataGrid1.DataSource = ds.Tables["Person"];
cnOra.Close();
Function GetEmailsByPageName(ByVal pageName As String) As DataSet
Dim cn As New OracleConnection
Dim cmd As New OracleCommand
cn = New OracleConnection
cn.ConnectionString = (ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString)
cmd = New OracleCommand("ORACLEDBA.PACKAGE_EMAIL.SP_EMAIL_LISTING_BY_NAME")
cmd.CommandType = Data.CommandType.StoredProcedure
cmd.Connection = cn
cmd.BindByName = True
Dim paramCursor As OracleParameter = New OracleParameter("email_list_cursor", OracleDbType.RefCursor)
With cmd.Parameters
.Add(New OracleParameter("a_page_name", OracleDbType.Varchar2)).Value = pageName
.Add("a_err_code", OracleDbType.Int32, Data.ParameterDirection.Output)
.Add("a_err_msg", OracleDbType.Varchar2, 300).Direction = Data.ParameterDirection.Output
.Add(paramCursor).Direction = Data.ParameterDirection.Output
End With
Dim da As New OracleDataAdapter(cmd)
Dim dsEmail As DataSet = New DataSet
Try
da.SelectCommand = cmd
da.Fill(dsEmail)
Return dsEmail
Catch ex As Exception
Throw
Finally
da.Dispose()
cmd.Dispose()
cn.Dispose()
If cn.State = ConnectionState.Open Then
cn.Close()
End If
End Try
End Function