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()
Related
I am trying learn how to use Access within VB.NET so i tried to make a simple application using an Access Database that can be used as a dictionary where someone can add some words int the database and then he can search for them.
My db contains two tables one with Word | Description and another one with Word | Synonym
The issue is that one word may have more than one Synonyms so i was thinking i could type all the synonyms in a textbox and using Regex.Split(" ") to split them and insert them in a loop. Can this be done with OleDbParameters?
This is what i have done so far but it only inserts the last record:
str = "insert into Synonyms ([Word],[Synonym]) values (#word,#synonym)"
cmd = New OleDbCommand(str, myConnection)
cmd.Parameters.Add(New OleDbParameter("Word", CType(txtWord.Text,
String)))
cmd.Parameters.Add("#synonym", OleDbType.VarChar)
Dim syn As String() = Regex.Split(txtSynonyms.Text, " ")
Dim i As Integer = 0
While i < syn.Length()
cmd.Parameters("#synonym").Value = syn(i)
i = i + 1
End While
Try
cmd.ExecuteNonQuery()
cmd.Dispose()
MsgBox("Synonyms for word """ & txtWord.Text & """ added")
txtWord.Clear()
txtSynonyms.Clear()
Catch ex As Exception
MsgBox(ex.Message)
End Try
myConnection.Open()
While i < syn.Length()
cmd.Parameters("#synonym").Value = syn(i)
cmd.ExecuteNonQuery()
i = i + 1
End While
myConnection.Close()
Maybe you will find this helpful.
Imports System.Data.OleDb
Public Class Form1
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
Dim con As New OleDb.OleDbConnection
Dim dbprovider As String
Dim dbsource As String
Dim ds As New DataSet
Dim da As OleDb.OleDbDataAdapter
Dim sql As String
Dim inc As Integer
dbprovider = "Provider=Microsoft.ACE.OLEDB.12.0;"
dbsource = "Data Source = C:\your_path_here\Nwind_Sample.accdb"
con.ConnectionString = dbprovider & dbsource
con.Open()
sql = "SELECT * FROM [OrderDetails]"
da = New OleDb.OleDbDataAdapter(sql, con)
da.Fill(ds, "OrderDetails")
Dim builder As New OleDbCommandBuilder(da)
Dim dsnewrow As DataRow
dsnewrow = ds.Tables("OrderDetails").NewRow()
dsnewrow.Item(0) = OrderID.Text
dsnewrow.Item(1) = ProductID.Text
dsnewrow.Item(2) = UnitPrice.Text
dsnewrow.Item(3) = Quantity.Text
dsnewrow.Item(4) = Discount.Text
'dsnewrow.Item(6) = True
ds.Tables("OrderDetails").Rows.Add(dsnewrow)
da.Update(ds, "OrderDetails")
End Sub
End Class
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"
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'm trying to figure out what's wrong with my code,
I'm trying to extract the value of employe ID selected from a dropdown, then get all information of that employee and place it in a textbox vb.net form, but there's a error whenever i select an employee ID
it's giving me an error message of : "An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in System.Data.dll
Additional information: No value given for one or more required parameters."
Thus highlighting reader, i'm not sure what's the problem, i have initialized the reader... Please guide me. Thanks
Private Sub eNumText_SelectedIndexChanged(sender As Object, e As EventArgs) Handles eNumText.SelectedIndexChanged
Dim dbSource = "Data Source= C:\Databse\Company_db.accdb"
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source= c:\Databse\Company_db.accdb"
Dim sqlQuery As String
Dim sqlCommand As New OleDbCommand
Dim sqlAdapter As New OleDbDataAdapter
Dim Table As New DataTable
Dim empNum As String
Dim empFname As String
Dim empLname As String
Dim empDept As String
Dim empStat As String
Dim empYears As String
empNum = eNumText.Text
empFname = empFnameText.Text
empLname = empLnameText.Text
empDept = DeptText.Text
empStat = StatText.Text
empYears = yearstext.Text
sqlQuery = "SELECT * FROM tbl_empinfo WHERE EmpID like empNum"
With sqlCommand
.CommandText = sqlQuery
.Connection = con
.Parameters.AddWithValue("EmpID", empNum)
With sqlAdapter
.SelectCommand = sqlCommand
.Fill(Table)
End With
With DataGridView1
.DataSource = Table
End With
End With
Dim path = "Data Source= C:\Databse\Company_db.accdb"
Dim command = "SELECT * FROM tbl_empinfo WHERE EmpID like empNum"
QueryData(path, Command)
con.Close()
End Sub
Private Sub QueryData(PathDb As String, command As String)
PathDb = "Data Source= C:\Databse\Company_db.accdb"
Using connection As New System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & PathDb)
Using da As New System.Data.OleDb.OleDbCommand(command, con)
con.Open()
Dim reader = da.ExecuteReader()
If reader.Read() Then
empFnameText.Text = reader("FirstName")
empLnameText.Text = reader("LastName")
End If
con.Close()
End Using
End Using
End Sub
You need to prefix your parameter empNum with an #: #empNum. See this answer: How to pass a parameter from vb.net for an example.
Hi guys I'm trying to search an employee information using SQL from MS Access, and hoping to put the fname lname and such details in their respective textbox which correspond to a specific employee's ID number. I have managed to make the SQL work but I don't know how to extract files from my sql statement and place it inside .text(text box), can you please guide me? Thanks
Here is my code so far:
(UPDATED my code) got an error message : Additional information: ExecuteReader: Connection property has not been initialized. Highlighting Reader below. How can i fix this? I'm trying to extract data and place it into the textbox? Thanks
Private Sub eNumText_SelectedIndexChanged(sender As Object, e As EventArgs) Handles eNumText.SelectedIndexChanged
Dim dbSource = "Data Source= C:\Databse\Company_db.accdb"
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source= c:\Databse\Company_db.accdb"
Dim sqlQuery As String
Dim sqlCommand As New OleDbCommand
Dim sqlAdapter As New OleDbDataAdapter
Dim Table As New DataTable
Dim empNum As String
Dim empFname As String
Dim empLname As String
Dim empDept As String
Dim empStat As String
Dim empYears As String
empNum = eNumText.Text
empFname = empFnameText.Text
empLname = empLnameText.Text
empDept = DeptText.Text
empStat = StatText.Text
empYears = yearstext.Text
sqlQuery = "SELECT * FROM tbl_empinfo WHERE EmpID like empNum"
With sqlCommand
.CommandText = sqlQuery
.Connection = con
.Parameters.AddWithValue("EmpID", empNum)
With sqlAdapter
.SelectCommand = sqlCommand
.Fill(Table)
End With
With DataGridView1
.DataSource = Table
End With
End With
Dim path = "Data Source= C:\Databse\Company_db.accdb"
Dim command = "SELECT * FROM tbl_empinfo WHERE EmpID like empNum"
QueryData(path, command)
con.Close()
End Sub
Private Sub QueryData(PathDb As String, command As String)
Using connection As New System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & PathDb)
Using da As New System.Data.OleDb.OleDbCommand(command, connection)
connection.Open()
Dim reader = da.ExecuteReader()
If reader.Read() Then
empFnameText.Text = reader("fname")
empLnameText.Text = reader("lname")
End If
connection.Close()
End Using
End Using
End Sub
for this, you need only this classes: Connection, Command, Reader.
Other classes in the code in question, some are redundant and some are required but in complicated than a simple case presentation.
Private Sub QueryData(PathDb As String, command As String)
Using connection As New System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & PathDb)
Using com As New System.Data.OleDb.OleDbCommand(command, connection)
connection.Open()
Dim reader = com.ExecuteReader()
If reader.Read() Then
TextBox1.text = reader("fname")
TextBox2.text = reader("lname")
End If
connection.Close()
End Using
End Using
End Sub
call the method so:
Dim path = "C:\Databse\Company_db.accdb"
Dim command = "SELECT * FROM tbl_empinfo WHERE EmpID like empNum"
QueryData(path, command)
EDIT - Use parameters:
Private Sub QueryData(PathDb As String, command As String, id As String)
Using connection As New System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & PathDb)
Using com As New System.Data.OleDb.OleDbCommand(command, connection)
com.Parameters.AddWithValue("", id)
connection.Open()
Using reader = com.ExecuteReader()
If reader.Read() Then
TextBox1.Text = reader("fname")
TextBox2.Text = reader("lname")
End If
End Using
connection.Close()
End Using
End Using
End Sub
Call the method:
Dim path = "C:\Databse\Company_db.accdb"
Dim command = "SELECT * FROM tbl_empinfo WHERE EmpID = ?"
Dim empNum = "..."
QueryData(path, command, empNum)