The result of my sql-query is a single value i want display that in a lable but dont know how. I have a solution creating a dataset put the result of the query into that dataset and get it by row(0),column(0) but i guess there is a smarter way doing it.
Private myquery As String
Sub New(ByVal query As String)
myquery = query
End Sub
Public Sub query_Send()
Dim myconn As New SqlConnection("Data Source=DB;Integrated Security=TRUE")
Dim mycmd As SqlCommand = New SqlCommand(Me.myQuery, myconn)
Dim myTable As New DataTable
Dim previousConnectionState As ConnectionState = myconn.State
Try
If myconn.State = ConnectionState.Closed Then
myconn.Open()
Dim myDA As New SqlDataAdapter(mycmd)
myDA.Fill(myTable)
tb.text = **...**
End If
If previousConnectionState = ConnectionState.Closed Then
myconn.Close()
End If
End Try
End Sub
You can use SqlCommand.ExecuteScalar Method
Dim querystr as String = "select value from MyTable where ID=5"
Dim mycmd As New SqlCommand(querystr, connection)
dim value as Object = mycmd.ExecuteScalar()
The value you can put to your textbox. ExecuteScalar returns first value of first row of the resultset (equivalent of row(0).column(0) ) When no record is returned the value is nothing.
Try something more along the lines of:
Using myconn As New SqlConnection("Data Source=DB;Integrated Security=TRUE")
Dim myDA As New SqlDataAdapter()
myDA.SelectCommand = New SqlCommand(myQuery, myconn)
myDA.Fill(myTable)
Return myTable
End Using
Or you can just get ahold of the first item in the first row with
myTable.Rows(0).ItemArray(0).ToString()
Related
How to call the datatable fill code without double in vb.net?.
in the code below you might see I wrote back the fill datatable code if there is a solution without me writing it back in "GenerateReport()". Please Recommend.
Thanks
Private WithEvents dt As New DataTable
Public Sub fillDataGridView1()
dt = New DataTable
Dim query As String = "SELECT NOD,ITM,CIA,DPR,QTY FROM RSD WHERE QTY > 0 AND PNM=#PNM"
Using con As OleDbConnection = New OleDbConnection(GetConnectionString)
Using cmd As OleDbCommand = New OleDbCommand(query, con)
cmd.Parameters.AddWithValue("#PNM", ComboBox1.SelectedValue)
Using da As New OleDbDataAdapter(cmd)
da.Fill(dt)
da.Dispose()
Dim totalColumn As New DataColumn()
totalColumn.DataType = System.Type.GetType("System.Double")
totalColumn.ColumnName = "Total"
totalColumn.Expression = "[CIA]*[QTY]*(1-[DPR]/100)"
dt.Columns.Add(totalColumn)
Me.grid.DataSource = dt
Me.grid.Refresh()
End Using
End Using
End Using
End Sub
Private Sub GenerateReport()
KtReport1.Clear()
'the code below actually already exists but I reuse it
dt = New DataTable
Dim query As String = "SELECT NOD,ITM,CIA,DPR,QTY FROM RSD WHERE QTY > 0 AND PNM=#PNM"
Using con As OleDbConnection = New OleDbConnection(GetConnectionString)
Using cmd As OleDbCommand = New OleDbCommand(query, con)
cmd.Parameters.AddWithValue("#PNM", ComboBox1.SelectedValue)
Using da As New OleDbDataAdapter(cmd)
da.Fill(dt)
Dim dtCloned As DataTable = dt.Clone()
dtCloned.Columns("CIA").DataType = GetType(String)
For Each row As DataRow In dt.Rows
dtCloned.ImportRow(row)
Next row
KtReport1.AddDataTable(dtCloned)
The issue is that you are essentially duplicating code despite the fact that you have a variable setup to hold the filled DataTable at the Form level.
What I would suggest doing is creating a function that returns the filled DataTable, then at the top of your two existing methods do a null check against the Form level variable.
Take a look at this example:
Private _dt As DataTable
Private Function GetAndFillDataTable() As DataTable
Dim dt As New DataTable()
Dim query As String = "SELECT NOD,ITM,CIA,DPR,QTY FROM RSD WHERE QTY > 0 AND PNM=#PNM"
Using con As OleDbConnection = New OleDbConnection(GetConnectionString)
Using cmd As OleDbCommand = New OleDbCommand(query, con)
cmd.Parameters.AddWithValue("#PNM", ComboBox1.SelectedValue)
Using da As New OleDbDataAdapter(cmd)
da.Fill(dt)
da.Dispose()
Dim totalColumn As New DataColumn()
totalColumn.DataType = System.Type.GetType("System.Double")
totalColumn.ColumnName = "Total"
totalColumn.Expression = "[CIA]*[QTY]*(1-[DPR]/100)"
dt.Columns.Add(totalColumn)
Return dt
End Using
End Using
End Using
End Function
Private Sub FillDataGridView1()
If (_dt Is Nothing) Then
_dt = GetAndFillDataTable()
End If
grid.DataSource = _dt
grid.Refresh()
End Sub
Private Sub GenerateReport()
If (_dt Is Nothing) Then
_dt = GetAndFillDataTable()
End If
Dim dtCloned As DataTable = _dt.Clone()
dtCloned.Columns("CIA").DataType = GetType(String)
For Each row In _dt.Rows
dtCloned.ImportRow(row)
Next row
KtReport1.AddDataTable(dtCloned)
End Sub
I have looked at many different code snippets on this site looking that would show me how to do something that should be fairly simple once I have the knowledge.
I want to query a database table for an array of values and then populate a combobox with those results.
Here is what I have so far:
Public Sub getMachines()
Try
Dim SQL As String = "SELECT MachineName from machine"
Form1.machineName.DisplayMember = "Text"
Dim tb As New DataTable
tb.Columns.Add("Text", GetType(String))
Using cn As New MySqlConnection(ConnectionString)
Using cmd As New MySqlCommand(SQL, cn)
For Each cmd As String In cmd
'I want to add each value found in the database to "tb.Rows.Add"
'tb.Rows.Add(???)
Next
Form1.machineName.DataSource = tb
cn.Open()
cmd.ExecuteNonQuery()
End Using
cn.Close()
End Using
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Sub
I proceeded much like you did. I used the Load method of the DataTable. It is not necessary to set the column name and type. The name of the column is taken from the Select statement and the datatype is inferred by ADO.net from the first few records.
Luckily a DataTable can be an Enumerable using the .AsEnumnerable method. Then we can use Linq to get all the values from the MachineName column. Calling .ToArray causes the Linq to execute. If you hold your cursor over names on this line you will see that the datatype is String(). Just what we need to fill a combo box.
Code for a class called DataAccess
Private ConnectionString As String = "Your Connection String"
Public Function GetMachineNames() As String()
Dim tb As New DataTable
Dim SQL As String = "SELECT MachineName from machine;"
Using cn As New MySqlConnection(ConnectionString)
Using cmd As New MySqlCommand(SQL, cn)
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
End Using
Dim names = dt.AsEnumerable().Select(Function(x) x.Field(Of String)("MachineName")).ToArray()
Return names
End Function
In the form load you combo box like this.
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim DatAcc As New DataAccess()
Dim arr = DatAcc.GetMachineNames()
machineName.DataSource = arr
End Sub
If you just want the MachineName to be displayed in the ComboBox, then just use that as the DisplayMember; don't bother creating another column called Text.
Public Sub getMachines()
Try
Dim cmd As String = "SELECT MachineName from machine"
Dim ds As New DataSet()
Using con As New MySqlConnection(ConnectionString)
Using da As New MySqlDataAdapter(cmd, con)
da.Fill(ds)
With Form1.machineName
.DisplayMember = "MachineName"
.ValueMember = "MachineName"
.DataSource = ds
End With
End Using
End Using
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Sub
I'll show a few examples, including using parameters, since that is important.
First up, a quick translation to run the existing query and loop through the results:
Public Sub getMachines()
Try
Dim SQL As String = "SELECT MachineName from machine"
Using cn As New MySqlConnection(ConnectionString), _
cmd As New MySqlCommand(SQL, cn)
cn.Open()
Using rdr As MySqlDatareader = cmd.ExecuteReader
While rdr.Read()
Form1.machineName.Items.Add(rdr("MachineName"))
End While
End Using
End Using
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Sub
But better practice for a method like this is to isolate data access for the UI. This method should return results to the caller, which can decide what do with them. So I'll show two methods: one to get the data, and the other to loop through it and set up the combobox:
Private Function GetMachines() As DataTable
'No try/catch needed here. Handle it in the UI level, instead
Dim SQL As String = "SELECT MachineName from machine"
Dim result As New DataTable
Using cn As New MySqlConnection(ConnectionString), _
cmd As New MySqlCommand(SQL, cn),
da As New MySqlDataAdapter(cmd)
da.Fill(result)
End Using
Return result
End Function
Public Sub LoadMachines()
Try
For Each item As DataRow in getMachines().Rows
Form1.machineName.Items.Add(item("MachineName"))
Next
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Sub
Or, we can use DataBinding:
Private Function GetMachines() As DataTable
Dim SQL As String = "SELECT MachineName from machine"
Dim result As New DataTable
Using cn As New MySqlConnection(ConnectionString), _
cmd As New MySqlCommand(SQL, cn),
da As New MySqlDataAdapter(cmd)
da.Fill(result)
End Using
Return result
End Function
Public Sub LoadMachines()
Try
Form1.machineName.DisplayMember = "FirstName";
Form1.machineName.ValueMember = "City"
Form1.machineName.DataSource = GetMachines()
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Sub
If you ever want to use a filter, you might do this (notice the overloading):
Private Function GetMachines(ByVal machineFilter As String) As DataTable
Dim SQL As String = "SELECT MachineName from machine WHERE MachineName LIKE #Filter"
Dim result As New DataTable
Using cn As New MySqlConnection(ConnectionString), _
cmd As New MySqlCommand(SQL, cn),
da As New MySqlDataAdapter(cmd)
'Match the MySqlDbType to your actual database column type and length
cmd.Parameters.Add("#Filter", MySqlDbType.VarString, 30).Value = machineFilter
da.Fill(result)
End Using
Return result
End Function
Private Function GetMachines(ByVal machineFilter As String) As DataTable
Return GetMachines("%")
End Function
Query parameters like that are very important, and if you were doing string concatenation to accomplish this kind of thing on your old platform, you were doing very bad things there, too.
Finally, let's get fancy. A lot of the time, you really don't want to load an entire result set into RAM, as is done with a DataTable. That can be bad. Instead, you'd like be able to stream results into memory and only work with one at a time, minimizing RAM use. In these cases, you get to play with a DataReader... but returning a DataReader object from within a Using block (which is important) doesn't work that well. To get around this, we can use functional programming concepts and advanced language features:
Private Iterator Function GetMachines(ByVal machineFilter As String) As IEnumerable(Of String)
Dim SQL As String = "SELECT MachineName from machine WHERE MachineName LIKE #Filter"
Using cn As New MySqlConnection(ConnectionString), _
cmd As New MySqlCommand(SQL, cn)
'Match the MySqlDbType to your actual database column type and length
cmd.Parameters.Add("#Filter", MySqlDbType.VarString, 30).Value = machineFilter
cn.Open()
Using rdr As MySqlDatareader = cmd.ExecuteReader
While rdr.Read()
Dim result As String = rdr("MachineName")
Yield Return result
End While
End Using
End Using
Return result
End Function
Private Function GetMachines() As IEnumerable(Of String)
Return GetMachines("%")
End Function
This is what I've got so far :
Dim myCONN As OleDbConnection = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=w:\Baza.mdb")
Dim cmd1 = New OleDbCommand("SELECT ID FROM Baza WHERE NAZIV=#XXNAZIV")
cmd1.Parameters.AddWithValue("#XXNAZIV", TextBox2.Text)
cmd1.Connection = myCONN
myCONN.Open()
Dim result = cmd1.ExecuteReader()
While (result.Read())
Dim rowx As Integer = GetTextOrEmpty(result("ID"))
End While
I've found the row (rowx) in which I would like to change values in 20 corresponding columns (namesID : NAZIV, SIFRA,...). Data is already presented in textboxes (textbox1...), but I don't know how to finish this code with UPDATE and how to insert changed values back to Access.
Dim cmdText As String = "UPDATE Baza SET NAZIV=#XXNAZIV Where ID=SomeId"
Using con = new OleDbConnection("PROVIDER=Microsoft.ACE.OLEDB.12.0;Data Source = h:\Baza.mdb")
Using cmd = new OleDbCommand(cmdText, con)
con.Open()
cmd.Parameters.AddWithValue("#XXNAZIV",TextBox2.Text)
cmd.ExecuteNonQuery()
End Using
End Using
This should help you to solve your problem, of course you will have to pass ID parameter to query also.
Reference
I want to select a certain field from a datatable in VB based on the value of another field in the same row.
In SQL, it would easily be done by writing this query:
select error_message from table_errors where error_case="condition"
How do I do this if I have my SQL table filled in a datatable in VB?
How do I select the item("error_message") in the datatable based on the item("error_Case") field?
Any help would be appreciated
You can use Linq-To-DataSet:
Dim matchingRows As IEnumerable(Of DataRow) =
From row In table
Where row.Field(Of String)("error_case") = "condition"
If you just want one column (of course that works also in one step):
Dim errorMessages As IEnumerable(Of String) =
From row In matchingRows
Select row.Field(Of String)("error_message")
For Each error In errorMessages
Console.WriteLine(error)
Next
If you expect it to be just a single row use First or Single(throws an exception if there is more than one row):
Dim error As String = errorMessages.First()
Since First throws an exception if the sequence is empty you can use FirstOrDefault:
Dim error As String = errorMessages.FirstOrDefault() ' is null/Nothing in case of an empty sequence
All in one line (note that both Linq and DataTable.Select needs to use loops):
Dim ErrMessage As String = errorTable.AsEnumerable().
Where(Function(r) r.Field(Of String)("Error_Case") = TextCase.Text).
Select(Function(r) r.Field(Of String)("Error_Message")).
FirstOrDefault()
here is a worker version of the rough code
Dim connString As String = "select error_message from table_errors where error_case='condition'"
Dim conn As SqlClient.SqlConnection = New SqlClient.SqlConnection(connString)
conn.Open()
Dim cmd As SqlClient.SqlCommand = New SqlClient.SqlCommand(connString, conn)
Dim dTable As DataTable = New DataTable()
Dim dAdapter As SqlClient.SqlDataAdapter = New SqlClient.SqlDataAdapter(cmd)
dAdapter.Fill(dTable)
conn.Close()
Dim text As String
Dim dReader As DataTableReader = dTable.CreateDataReader()
While dReader.Read()
text = dReader.GetValue(0)
End While
dReader.Close()
I want to save a record in the database using a dataset, but my data is not committing into my database.
My code can be viewed below:
Dim mydataset1 As New MyDataSet
Dim row As DataRow = mydataset1.Tables("testtable").NewRow()
With row
.Item("name") = "Segun Omotayo"
.Item("address") = "Abuja"
End With
mydataset1.Tables("testtable").Rows.Add(row)
Any help will be appreciated
A DataSet/DataTable is a offline/in-memory representation of your database. If you want to update the database, you need to use a DataAdapter.
For example (assuming you're using MS-Sql-Server):
Public Function UpdateDataSet(dataSet As DataSet) As Int32
Using con = New SqlConnection(My.Settings.SqlConnection)
Dim sql = "INSERT INTO TUser(Name,Address)VALUES(#Name,#Address)"
Using cmd = New SqlCommand(sql, con)
cmd.Parameters.Add(New SqlParameter("#Name", SqlDbType.VarChar))
cmd.Parameters.Add(New SqlParameter("#Address", SqlDbType.VarChar))
Using da = New SqlDataAdapter()
da.InsertCommand = cmd
con.Open()
Dim rowCount = da.Update(dataSet)
Return rowCount
End Using
End Using
End Using
End Function
I could be rusty here since its a long time since I wrote any VB.NET or used data adapters/datasets/datatables but I think if you decide to take that route you would need code like this:
Dim connection As New SqlConnection("#####YourConnectionString#####")
connection.Open()
Dim adapter As New SqlDataAdapter("SELECT * FROM testtable", connection)
' For the line below to work, you must have a primary key field in "testtable"
Dim builder As New SqlCommandBuilder(adapter)
Dim testtable As New DataTable("testtable")
adapter.Fill(testtable)
Dim row As DataRow = testtable.NewRow()
With row
.Item("name") = "Segun Omotayo"
.Item("address") = "Abuja"
End With
testtable.Rows.Add(row)
adapter.Update(testtable)
connection.Close()