I have a dialog with a combobox listing the years an event was held.
Changing the year, changes the following list boxes
One list box 'called inEvent' shows all golfers the attended said event.
The other list box called 'available' that shows every golfer we have in our database that did not attend that years event
It has two buttons. One removes golfers from 'inEvent' and moves them to 'available'. This button works.
The other button does the opposite. It adds available golfers to the selected event year. But it gives me the error -
"The statement has been terminated. Cannot insert the value NULL into column 'intGolferEventYearID', table 'dbo.TGolferEventYears'; column does not allow nulls. INSERT fails."
Changing any line of code in VB results in a different error. So I think the error has to come from SQL itself which I don't know much about. Only other thing I can think of is the listbox is giving the wrong information.
Private Sub btnAddAuto_Click(sender As Object, e As EventArgs) Handles btnAddAuto.Click
Dim strInsert As String = ""
Dim cmdInsert As OleDb.OleDbCommand ' used for our Select statement
Dim dt As DataTable = New DataTable ' table we will load from our reader
Dim intRowsAffected As Integer
' open the DB
OpenDatabaseConnectionSQLServer()
' Build the select statement
strInsert = "INSERT INTO TGolferEventYears ( intGolferID, intEventYearID) Values (" & lstAvailable.SelectedValue & ", " & cboEvents.SelectedIndex + 1 & ")"
' Retrieve all the records
cmdInsert = New OleDb.OleDbCommand(strInsert, m_conAdministrator)
intRowsAffected = cmdInsert.ExecuteNonQuery()
' close the database connection and reload the form so the changes are shown
CloseDatabaseConnection()
frmEventsGolfers_Load(sender, e)
End Sub
I separated the data access code from the user interface. This will make it easy to remove data access entirely from the Form if you later desire.
Private Sub MoveGolfer(GolfID As Integer, YearID As Integer)
'If you keep your connections local you can be sure they are
'closed and disposed which is what the Using...End Using blocks do.
Using cn As New SqlConnection("Your connection string")
Using cmd As New SqlCommand("INSERT INTO TGolferEventYears ( intGolferID, intEventYearID) Values (#Golf, #Year;")
'Always use parameters to protect against Sql injection
cmd.Parameters.Add("#Golf", SqlDbType.Int).Value = GolfID
cmd.Parameters.Add("#Year", SqlDbType.Int).Value = YearID
cn.Open()
cmd.ExecuteNonQuery()
End Using
End Using
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim GolferID As Integer = CInt(lstAvailable.SelectedValue)
Dim Year As Integer = cboEvents.SelectedIndex + 1
Try
MoveGolfer(GolferID, Year)
Catch ex As Exception
'Catch a more specific exception and handle accordingly
MessageBox.Show(ex.Message)
End Try
End Sub
Since I don't really understand SQL I didn't realize my PK didn't have the IDENTITY tag added in the table. Adding this fixed my issue.
Here is the code I added
Dim strSelect As String
Dim cmdSelect As OleDb.OleDbCommand
Dim drSourceTable As OleDb.OleDbDataReader
Dim intNextHighestRecordID As
strSelect = "SELECT MAX(intDealerAutos) + 1 AS intNextHighestRecordID " &
" FROM TDealerAutos"
'Excute command
cmdSelect = New OleDb.OleDbCommand(strSelect, m_conAdministrator)
drSourceTable = cmdSelect.ExecuteReader
'Read result( highest ID )
drSourceTable.Read()
'Null? (Empty Table)
If drSourceTable.IsDBNull(0) = True Then
'Yes, start numbering at 1
intNextHighestRecordID = 1
Else
'No, get the next highest ID
intNextHighestRecordID = CInt(drSourceTable.Item(0))
End If
'Build the select statement
strInsert = "INSERT INTO TDealerAutos ( intDealerAutos, intDealerID, intAutoID)" &
"Values (" & intNextHighestRecordID & ", " & cboDealers.SelectedValue & ", " & lstAvailable.SelectedValue & ")"
Related
I have a problem on making avoid or detect duplicate data entry in VB.NET using SQL Server, and also pop up message when there is duplicate entry.
This is my add button code:
Dim sql = "INSERT INTO studentAttendence(studentID, date, time, subject, attendence) " &
"VALUES(#studentID, #date, #time, #subject, #attendence)" &
"WHERE NOT EXISTS(SELECT * FROM studentAttendence WHERE studentID = #studentID)"
Using cn As New SqlConnection("My sql Connection string")
Dim commands As SqlCommand = New SqlCommand(sql, cn)
commands.Parameters.Add("#studentID", SqlDbType.NVarChar).Value = TextBox1.Text
commands.Parameters.Add("#date", SqlDbType.NVarChar).Value = DateTimePicker1.Text
commands.Parameters.Add("#time", SqlDbType.NVarChar).Value = DateTimePicker2.Text
commands.Parameters.Add("#subject", SqlDbType.NVarChar).Value = ComboBox1.Text
commands.Parameters.Add("#attendence", SqlDbType.NVarChar).Value = ComboBox2.Text
commands.ExecuteNonQuery()
End Using
Or is there any other methods for making avoid duplicate entries. I just want to avoid same date and subject of a student to add. So I can only add subject on the next date if I already add subject on today's date of studentID.
You can use If Not Exists before the insert. This method only requires a single hit on the database. Add a comman at the end of the first line of the Using block, then delete Dim before commands. This will include commands in the Using block.
Private Function InsertAttendance() As Integer
Dim sql = "If Not Exists (Select 1 From studentAttendence
Where studnetID = #studentID And date = #date And subject = #subject)
INSERT INTO studentAttendence(studentID, date, time, subject, attendence)
VALUES(#studentID, #date, #time, #subject, #attendence);"
Dim NumRowsAffected As Integer
Using cn As New SqlConnection("My sql Connection string"),
commands As SqlCommand = New SqlCommand(sql, cn)
commands.Parameters.Add("#studentID", SqlDbType.NVarChar).Value = TextBox1.Text
commands.Parameters.Add("#date", SqlDbType.NVarChar).Value = DateTimePicker1.Text
commands.Parameters.Add("#time", SqlDbType.NVarChar).Value = DateTimePicker2.Text
commands.Parameters.Add("#subject", SqlDbType.NVarChar).Value = ComboBox1.Text
commands.Parameters.Add("#attendence", SqlDbType.NVarChar).Value = ComboBox2.Text
cn.Open()
NumRowsAffected = commands.ExecuteNonQuery()
End Using
Return NumRowsAffected
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Try
If InsertAttendance() = 1 Then
MessageBox.Show("Success")
Else
MessageBox.Show("Duplicate Entry")
End If
Catch ex As Exception
MessageBox.Show($"Error Entering Attendance {ex.Message}")
End Try
End Sub
Be sure to check the datatypes of your parameters with the database.
You should create a function that queries your data table to return the row count where the Date, Subject, and StudentId match what you're wanting to insert. If the returned result is greater than 0 then display the message.
Here is a function that returns -1 if something went wrong or the row count:
Private Function GetRowCount(ByVal studentIdParameter As String, ByVal dateParameter As DateTime, ByVal subjectParameter As String) As Integer
'Declare the object to return
Dim count As Integer = -1
'Declare the connection object
Dim con As OleDbConnection
'Wrap code in Try/Catch
Try
'Set the connection object to a new instance
'TODO: Change "My Connection String Here" with a valid connection string
con = New OleDbConnection("My Connection String Here")
'Create a new instance of the command object
'TODO: Change [ID] to a valid column
Using cmd As OleDbCommand = New OleDbCommand("SELECT Count([ID]) FROM [MyTable] WHERE studentID=#studentId, AND date=#date AND subject=#subject", con)
'Parameterize the query
cmd.Parameters.Add("#studentId", OleDbType.NVarChar).Value = studentIdParameter
cmd.Parameters.Add("#date", OleDbType.DBDate).Value = dateParameter.Date
cmd.Parameters.Add("#subject", OleDbType.NVarChar).Value = subjectParameter
'Open the connection
con.Open()
'Use ExecuteScalar to return a single value
count = Convert.ToInt32(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
'Return the row count
Return count
End Function
To implement it, you'd do something like:
Dim rowCount = GetRowCount(TextBox1.Text, DateTimePicker1.Value, ComboBox1.Text)
If (rowCount = -1) Then
MessageBox.Show("Something went wrong checking for duplicates")
ElseIf (rowCount = 0) Then
' Insert record
Else
MessageBox.Show("A record already exists with this studentId, date, and subject.")
End If
I am attempting to pull values from an SQL Server table from VB.NET.
On VB Form 1, the number from NoTable, Row 1, is pulled successfully, and Label1 is updated with the value.
Dim command As SqlCommand
Dim query As String = "SELECT Number FROM NoTable"
command = New SqlCommand(query, con)
con.Open()
Dim datareader As SqlDataReader = cmd.ExecuteReader()
If datareader.Read() Then
Label1.Text = datareader.GetValue(0)
End If
datareader.Close()
On VB Form 2 I am attempting to pull the value from the second row, using:
Dim query As String = "SELECT Number FROM NoTable"
command = New SqlCommand(query, con)
con.Open()
Dim datareader As SqlDataReader = cmd.ExecuteReader()
If datareader.Read() Then
Label1.Text = datareader.GetValue(1)
End If
datareader.Close()
However, this does not work, and the label is not updated with the value from the second row.
An unhandled exception of type 'System.IndexOutOfRangeException' occurred in System.Data.dll
Additional information: Index was outside the bounds of the array."
How would I go about fixing this, so that on Form 2, the value from Row 2 is pulled, and so forth?
Thank you.
Firstly, you only get one column back from the reader, but you are indexing the columns with that 0 or 1. So you should always pass 0 to GetValue.
To index the row instead, try this. Assign a form number to each form (first line in my example) and use that to determine which record to assign to the Label. There is probably a more efficient way to do this (not returning all the records before it) but this solution should fit in your environment.
' in form # 1
Dim formNumber = 1
Dim command As SqlCommand
Dim query As String = "SELECT Number FROM NoTable"
command = New SqlCommand(query, con)
con.Open()
Dim datareader As SqlDataReader = cmd.ExecuteReader()
Dim index = 0
While index < formNumber
If datareader.Read() AndAlso index = formNumber Then
Label1.Text = datareader.GetValue(0)
End If
index += 1
End While
datareader.Close()
See https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getvalue(v=vs.110).aspx
And another similar question in c# Access a specific row in DataReader
Another way is to just return the row you need in the first place, without iterating over the records on the client side. Assuming there is another column with an index which is in the same order as the row you want to return, called "ID"
' in form # 1
Dim formNumber = 1
Dim command As SqlCommand
Dim query As String =
"SELECT Number FROM " & _
" (SELECT Number, Row_Number() OVER (ORDER BY ID) AS RowNumber " & _
" FROM NoTable) AS Results " & _
" WHERE Results.RowNumber = " & formNumber.ToString()
command = New SqlCommand(query, con)
con.Open()
Dim datareader As SqlDataReader = cmd.ExecuteReader()
Label1.Text = datareader.GetValue(0)
datareader.Close()
See https://msdn.microsoft.com/en-us/library/ms186734.aspx
GetValue(1) does not exist, as this would refer to a second column in the select statement. You are only asking for [Number] which would be datareader.GetValue(0)
I'm looking for a way to set the next value of a row into a label
without using a Binding Navigator. ex: when I click the next button the next username in the username column should appear on the label and keep rolling the names.
Actually planing to make a quiz so I want to 'roll' the question.
What I've tried
I have bound data(ex: usernames) to a label using its property (Data Bindings). Now how can I display them in the label and with each button press have the next one appear?
OK, this is what did to achieve that on alternative way:
but this not working
I'm getting this error >> Syntax error in string in query expression 'tagno='2'. # line dr = Command.ExecuteReader
The objective is to on button click the count integer will increment and then the query will use count value to find question from database
for example if the increment value is 2 then the reader should return question from row where tagno two is.
the database table (quest) has following columns, Question Correct_Answer, tagno
Dim count As Integer
Private Sub btncontinue_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btncontinue.Click
Dim conn As New OleDb.OleDbConnection
Dim olequery As New OleDb.OleDbCommand
Dim connString As String
connString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=\" & Application.StartupPath & "\game.accdb"
conn.ConnectionString = connString
olequery.Connection = conn
count += 1
Dim dr As OleDbDataReader
'quest is the table name.
Dim query As String = "select question from quest where tagno='" & count & ""
cnnOLEDB.Open()
Dim command As New OleDbCommand(query, cnnOLEDB)
dr = Command.ExecuteReader
dr.Read()
lblquestion.Text = dr(0)
cnnOLEDB.Close()
End Sub
I am inserting values in datagrid from MS-SQL server. I got a text box from which i wanted to perform search operation , but the thing is i haven't used data set.
the question is How do i search for values in datagrid without using data set in vb.net.
Here is my code fr filling up data grid view.
dim i as integer = 0
con.ConnectionString = "Data Source=MY_CONNECTION_STRING "
Dim cmd As New SqlCommand("selct ID, Name From tbl_name where 1=1 Order by Name ASC", con)
con.Open()
' Execute Query
Dim reader As SqlDataReader = cmd.ExecuteReader()
' Try
While reader.Read()
DataGridView10.Rows.Insert(i, New String() {reader(0), reader(1).ToString})
i = i + 1
End While
You can put this in a click event per say...
Private Sub btnSearch_Click(sender As Object, e As EventArgs) Handles btnSearch.Click
Dim intIndex As Integer = SearchGrid(TextBox1.Text, 0) 'Change the 0 to what column you want to search for
DataGridView1.Rows(intIndex).Selected = True 'This will select the row...'
DataGridView1.CurrentCell = DataGridView1.Rows(intIndex).Cells(0) 'This ensures that the arrow will move if you have row headers visible. In order to select the cell change the zero to the column your searching to match up top
End Sub
Here's the function...
Private Function SearchGrid(ByVal strItem As String, ByVal intColumn As Integer) As Integer
Dim intIndex As Integer = 0
For i As Integer = 0 To DataGridView1.Rows.Count - 1
If DataGridView1.Rows(i).Cells(intColumn).Value.ToString.Contains(strItem) Then 'Or change "Contains" to "Equals"
intIndex = i
Exit For
End If
Next
Return intIndex
End Function
This will work great for you and a great start, happy coding!
P.S. Make sure to change the datagridview name to reflect yours...
the code below returns the fields of a given table ("Employee"), but I need to return the fields of ALL the tables in the given database, is this possible? My assumption is a For loop which loops round the tables in the database and prints the corresponding fields but my efforts seem to be in vain
Public Sub getDbFields()
Dim i As Integer
Dim dbcon As New System.Data.OleDb.OleDbConnection("PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = " & dblocation & _
"\" & dbname)
Try
dbcon.Open()
dbDt = dbcon.GetOleDbSchemaTable(OleDb.OleDbSchemaGuid.Columns, New Object() _
{Nothing, Nothing, "Employee", Nothing})
For i = 0 To dbDt.Rows.Count - 1
'compile lbtables with a list of available tables from the database
newLine()
frmMain.lstTables.Items.Add(dbDt.Rows(i)!COLUMN_NAME.ToString())
Next
Catch ex As Exception
MessageBox.Show(ex.Message.ToString(), "Data Load Error", MessageBoxButtons.OK,
MessageBoxIcon.Exclamation)
End Try
End Sub
This routine will be fired from the selection of a checkbox
This will return all columns on a database
Using con = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;" +
"Data Source=" + dblocation + "\" + dbname)
con.Open()
Dim schema as DataTable = con.GetSchema("COLUMNS")
Dim dr as DataRow
For Each dr in schema.Rows
Dim tablename as string = dr("TABLE_NAME").ToString()
if Not tablename.StartsWith("MSys") then
Console.WriteLine(dr("TABLE_NAME").ToString() + " " + dr("COLUMN_NAME").ToString())
End if
Next
End Using
Please note that the bang (!) syntax is not allowed in vb.net.
Also your code could work if you change
dbDt = dbcon.GetOleDbSchemaTable(OleDb.OleDbSchemaGuid.Columns, New Object() _
{Nothing, Nothing, Nothing, Nothing})
and this line
frmMain.lstTables.Items.Add(dbDt.Rows(i)("COLUMN_NAME").ToString())