I'm writing a calorie counter tool for my girlfriend...
But I've run in to an issue I really cant figure out...
I have place in my script where I would wanna take some information out from my db...
The specific place in the script thats teasing, is the one that will take out data from a row called "antal" from a table called "items".
One place in my script, I call "navn" from items, and it works perfect...
This other place, it gives me the error that there isn't any data in the row!
My code looks so far like this:
Imports System.Data.OleDb
Private Sub ins_kat_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ins_kat.SelectedIndexChanged
Dim Con = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\Privat\MCC\mccdb.mdb")
Con.Open()
Dim command As OleDbCommand = New OleDbCommand("SELECT * FROM items WHERE kat = '" & ins_kat.Text & "' ORDER BY id DESC", Con)
Dim read As OleDbDataReader = command.ExecuteReader()
ins_mad.Items.Clear()
While read.Read()
ins_mad.Items.Add(read.Item("navn")) '<---- This place works!!!
End While
Con.Close()
End Sub
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim ialt_c_counter As String
Dim ialt_c_counter_conv As Decimal
Dim ialt_c_counter_conv2 As Decimal
Dim ialt_counter As String
Dim ialt_final As Decimal
Dim Con = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\Privat\MCC\mccdb.mdb")
Con.Open()
Dim command1 As OleDbCommand = New OleDbCommand("SELECT * FROM food WHERE dag = '" & stat_dag.Text & "' AND maaned = '" & stat_maaned1.Text & "' AND aar = '" & stat_aar1.Text & "'", Con)
Dim read1 As OleDbDataReader = command1.ExecuteReader()
While read1.Read()
ialt_c_counter = read1.Item("antal")
ialt_c_counter_conv = System.Convert.ToDecimal(ialt_c_counter)
Dim commandX As OleDbCommand = New OleDbCommand("SELECT * FROM items", Con)
Dim reader As OleDbDataReader = commandX.ExecuteReader()
ialt_counter = reader.Item("antal") '<--- THIS ONE is giving me the error!!
ialt_c_counter_conv2 = System.Convert.ToDecimal(ialt_counter)
ialt_final = (ialt_c_counter_conv / 100 * ialt_c_counter_conv2) + ialt_final
End While
Con.Close()
MsgBox(ialt_final)
End Sub
End Class
By now, I want a MsgBox telling me the result of my algorithm, but I don't even get that far cause of the error message...
I guess the error you see is
InvalidOperationException: Invalid attempt to read when no data is present.
You never call Read() on the OleDbDataReader called reader.
Note how you use a While loop to call Read() for read and read1, but not reader (bad variable names, btw).
Related
Im trying to edit items after inserting to access by clicking the save button? How can i save the edits done in datagridview rows to access?
Already tried the update query
For each loop
vb.net
Private Sub BunifuFlatButton1_Click(sender As Object, e As EventArgs) Handles BunifuFlatButton1.Click
Dim constring As String = ("Provider=Microsoft.ACE.OLEDB.12.0;Data Source= C:\Users\PU-IMO\Desktop\BlueWavesIS - Copy\BlueWavesIS\BlueWavesIS.accdb")
Dim conn As New OleDbConnection(constring)
For Each row As DataGridViewRow In DataGridView1.Rows
Using con As New OleDbConnection(constring)
'nettxt.Text = (grosstxt.Text * perdistxt.Text / 100) - (dislctxt.Text + disusd.Text + distax.Text)
Dim cmd As New OleDbCommand("Update PurchaseInvoice set [Itemnum] = #ItemNum, [Itemname]= #ItemName, [Itemqty]= #ItemQty, [Itemprice] = #ItemPrice, [discount] =#discount, [subtotal] = #subtotal,[Preference] = " & preftxt.Text & ", [Suppnum] = " & pnumtxt.Text & ", [UniqueID] = " & pautotxt.Text & " Where [UniqueID] = " & pautotxt.Text & "", con)
cmd.Parameters.AddWithValue("#ItemID", row.Cells("ItemID").Value)
cmd.Parameters.AddWithValue("#ItemName", row.Cells("ItemName").Value)
cmd.Parameters.AddWithValue("#ItemQty", row.Cells("ItemQty").Value)
cmd.Parameters.AddWithValue("#ItemPrice", row.Cells("ItemPrice").Value)
cmd.Parameters.AddWithValue("#discount", row.Cells("discount").Value)
cmd.Parameters.AddWithValue("#subtotal", row.Cells("subtotal").Value)
cmd.Parameters.AddWithValue("#Ref", preftxt.Text.ToString)
cmd.Parameters.AddWithValue("#Suppnum", Convert.ToInt32(pnumtxt.Text))
cmd.Parameters.AddWithValue("#UniqueID", Convert.ToInt32(pautotxt.Text))
DataGridView1.AllowUserToAddRows = False
con.Open()
cmd.ExecuteNonQuery()
con.Close()
End Using
Next
'This the code i used to show the data in datagridview:
Private Sub NewPurchaseInvoice_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim con As New OleDbConnection
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source= C:\Users\PU-IMO\Desktop\BlueWavesIS - Copy\BlueWavesIS\BlueWavesIS.accdb"
con.Open()
Dim sql As String = "Select [Itemnum],[Itemname],[Itemprice],[ItemQty],[discount],[subtotal] from PurchaseInvoice where [UniqueID] = " & pautotxt.Text & ""
Dim cmd10 As OleDbCommand = New OleDbCommand(Sql, con)
'Dim adap As New OleDbDataAdapter("Select [Itemnum],[Itemname],[Itemprice],[discount],[subtotal] from PurchaseInvoice where UniqueID = " & pautotxt.Text & "", con)
'Dim ds As New System.Data.DataSet
'adap.Fill(ds, "PurchaseInvoice")
Dim dr As OleDbDataReader = cmd10.ExecuteReader
Do While dr.Read()
DataGridView1.Rows.Add(dr("ItemNum"), dr("ItemName"), dr("ItemQty"), dr("ItemPrice"), dr("discount"), dr("subtotal"))
Loop
con.Close()
I expect that all the rows will be updated as each other, but the actual output is that each row has different qty name etc...
This code does not seem appropriate in the load event because pautotxt.Text will not have a value yet. Can you move it to a Button.Click?
I guessed that the datatype of ID is an Integer. You must first test if the the .Text property can be converted to an Integer. .TryParse does this. It returns a Boolean and fills IntID that was provided as the second parameter.
You can pass the connection string directly to the constructor of the connection. The Using...End Using blocks ensure that your database objects are closed and disposed even if there is an error. You can pass the Select statement and the connection directly to the constructor of the command.
ALWAYS use Parameters, never concatenate strings to avoid sql injection. Don't use .AddWithValue. See http://www.dbdelta.com/addwithvalue-is-evil/
and
https://blogs.msmvps.com/jcoehoorn/blog/2014/05/12/can-we-stop-using-addwithvalue-already/
and another one:
https://dba.stackexchange.com/questions/195937/addwithvalue-performance-and-plan-cache-implications
The DataAdapter will open the connection, fiil the DataTable and close the connection if it finds it closed; however if it is found open it will leave it open.
The last line binds the grid to the DataTable.
Private Sub FillGrid()
If Not Integer.TryParse(pautotxt.Text, IntID) Then
MessageBox.Show("Please enter a number")
Return
End If
dt = New DataTable()
Using con As New OleDbConnection(ConnString)
Using cmd As New OleDbCommand(Sql, con)
cmd.Parameters.Add("#ID", OleDbType.Integer).Value = IntID
Dim adap = New OleDbDataAdapter(cmd)
adap.Fill(dt)
End Using
End Using
DataGridView1.DataSource = dt
End Sub
DataTables are very clever. When bound to a DataGridView they keep track of changes and mark rows as update, insert, or delete. The DataAdapter uses this info to update the database. Once the database is updated we call .AcceptChanges on the DataTable to clear the marking on the rows.
Private Sub UpdateDatabase()
Using cn As New OleDbConnection(ConnString)
Using da As New OleDbDataAdapter(Sql, cn)
da.SelectCommand.Parameters.Add("#ID", OleDbType.Integer).Value = IntID
Using builder As New OleDbCommandBuilder(da)
da.Update(dt)
End Using
End Using
End Using
dt.AcceptChanges()
End Sub
I have the following code and through debugging the problem begins at the While loop. I am trying to retrieve information from 2 tables and insert it into the table created. The information is not being inserted into the table and I am getting blank rows.
Imports System.Data.OleDb
Public Class RouteToCruise
Private Sub RouteToCruise_Load(sender As Object, e As EventArgs) Handles MyBase.Load
End Sub
Private Sub Route_Btn_Click(sender As Object, e As EventArgs) Handles Route_Btn.Click
Dim row As String
Dim connectString As String = "Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source=M:\ICT-Group-Project\DeepBlueProject\DeepBlueProject\DeepBlueTables.mdb"
Dim cn As OleDbConnection = New OleDbConnection(connectString)
cn.Open()
Dim CruiseQuery As String = "SELECT CruiseID, RouteID FROM Cruise WHERE CruiseID =?"
Dim RouteQuery As String = "SELECT RouteName FROM Route WHERE RouteID =?"
Dim cmd As OleDbCommand = New OleDbCommand(CruiseQuery, cn)
Dim cmd2 As OleDbCommand = New OleDbCommand(RouteQuery, cn)
cmd.Parameters.AddWithValue("?", Route_Txt.Text)
Dim reader As OleDbDataReader
reader = cmd.ExecuteReader
'RCTable.Width = Unit.Percentage(90.0)
RCTable.ColumnCount = 2
RCTable.Rows.Add()
RCTable.Columns(0).Name = "CruiseID"
RCTable.Columns(1).Name = "Route"
While reader.Read()
Dim rID As String = reader("RouteID").ToString()
cmd2.Parameters.AddWithValue("?", rID)
Dim reader2 As OleDbDataReader = cmd2.ExecuteReader()
'MsgBox(reader.GetValue(0) & "," & reader.GetValue(1))
row = reader("CruiseID") & "," & reader2("RouteName")
RCTable.Rows.Add(row)
cmd.ExecuteNonQuery()
reader2.Close()
End While
reader.Close()
cn.Close()
End Sub
End Class
If I understand your tables structure well then you could just run a single query extracting data from the two table and joining them in a new table returned by the query
Dim sql = "SELECT c.CruiseID c.CruiseID & ',' & r.RouteName as Route " & _
"FROM Cruise c INNER JOIN Route r ON c.RouteID = c.RouteID " & _
" WHERE c.CruiseID = #cruiseID"
Dim cmd As OleDbCommand = New OleDbCommand(sql, cn)
cmd.Parameters.Add("#cruiseID", OleDbType.Int).Value = Convert.ToInt32(Route_Txt.Text)
Dim RCTable = new DataTable()
Dim reader = cmd.ExecuteReader()
reader.Load(RCTable)
At this point the RCTable is filled with the data coming from the two tables and selected using the Route_Txt textbox converted to an integer. If the CruiseID field is not a numeric field then you should create the parameter as of type OleDbType.VarWChar and remove the conversion to integer
Try simplifying your query.
Dim CruiseRouteQuery As String = "SELECT C.CruiseID, C.RoutID, R.Routename FROM Cruise C LEFT JOIN Route R ON C.RouteID = R.RoutID WHERE CruiseID =?"
Also, please let us know what errors you are getting.
I want a specific value of an SQL Database column to appear in a textbox, but there is an error with my code which appears to be at this line:
Dim lrd As MySqlDataReader = cmd.ExecuteReader()
Imports MySql.Data.MySqlClient
Public Class Main
Dim conn As MySqlConnection
Private Sub Main_Load(sender As Object, e As EventArgs) Handles Me.Load
conn = New MySqlConnection()
conn.ConnectionString = "server='127.0.0.1';user id='root';Password='test';database='snipper'"
Try
conn.Open()
Catch myerror As MySqlException
MsgBox("Error Connecting to Database. Please Try again !")
End Try
Dim strSQL As String = "SELECT * FROM snippets"
Dim da As New MySqlDataAdapter(strSQL, conn)
Dim ds As New DataSet
da.Fill(ds, "snippets")
With ComboBox1
.DataSource = ds.Tables("snippets")
.DisplayMember = "title"
.SelectedIndex = 0
End With
Dim cmd = New MySqlCommand("SELECT snippet FROM snippets where title=" & cbSnippets.Text)
cmd.Connection = conn
Dim lrd As MySqlDataReader = cmd.ExecuteReader()
While lrd.Read()
txtCode.Text = lrd("snippet").ToString()
End While
End Sub
What may be wrong?
PLEASE USE PARAMETERISED QUERIES
Your actual problem originates from this line:
Dim cmd = New MySqlCommand("SELECT snippet FROM snippets where title=" & cbSnippets.Text)
Supposing I enter "This is a test" into the text box, the SQL becomes
SELECT snippet
FROM snippets
WHERE title=This is a test
With no quotes around the text, it should be:
SELECT snippet
FROM snippets
WHERE title='This is a test'
However, if I were to write "''; DROP TABLE Snippets; -- " In your text box you may find yourself without a snippets table!.
You should always use parameterised queries, this is safer and more efficient (it means query plans can be cached and reused so don't need to be compiled each time);
Dim cmd = New MySqlCommand("SELECT snippet FROM snippets where title = #Title")
cmd.Parameters.AddWithValue("#Title", cbSnippets.Text)
Dim lrd As MySqlDataReader = cmd.ExecuteReader()
Try changing this line :
Dim cmd = New MySqlCommand("SELECT snippet FROM snippets where title=" & cbSnippets.Text)
to :
Dim cmd = New MySqlCommand("SELECT snippet FROM snippets where title='" & cbSnippets.Text & "'")
Note the quotes around the string you'l be searching for. You could aswell use the like comparison too :
Dim cmd = New MySqlCommand("SELECT snippet FROM snippets where title like '%" & cbSnippets.Text & "%'")
The % symbol acts as a wildcard. In this case, that would look for any string containing the searched text instead of string being exactly the same as the searched text.
I have problem with data that needs to be seen on datagridview. Bellow is my code:
Public Class Form3
Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim CONNECT_STRING As String = (...)
Dim cnn As New OleDbConnection(CONNECT_STRING)
cnn.Open()
MsgBox(status_narocila.value)
Dim sql As String = "SELECT artikel.st_artikla, artikel.naziv_artikla, narocilo.kolicina, narocilo.barva_tiska, narocilo.izvedba, narocilo.opombe, narocilo.datum_narocila, narocilo.rok_izdelave, narocilo.status, narocilo.ID FROM (narocilo INNER JOIN artikel ON narocilo.id_artkla = artikel.ID) WHERE(narocilo.ID = '" & status_narocila.value & "')"
Dim cmd As New OleDbCommand(sql, cnn)
Dim da As New OleDbDataAdapter(cmd)
Dim ds As New DataSet
da.Fill(ds, "artikel")
cnn.Close()
DataGridView1.DataSource = ds.Tables("artikel")
End Sub
End Class
Value status.narocila.value is integer, I've tested it and getting right value from it. The code is working fine without WHERE clause.
= '" & status_narocila.value & "')"
should be
= " & status_narocila.value & ")"
no ' on numeric data types.
If narocilo.ID is also an integer, then the problem is you're using text qualifers on an integer field.
Try changing your WHERE clause to:
WHERE(narocilo.ID = " & status_narocila.value & ")"
I am using MS Access Database. Now I have to update a particular cell value. Here is my code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim str As String
Dim Presc As New System.Text.StringBuilder
Dim prs As String(), j As Integer
prs = Split(txtPrescription.Text, vbCrLf)
For j = 0 To prs.Length - 1
Presc.Append(prs(j))
Presc.Append(",")
Next
Try
str = Trim(lsvCase.SelectedItems(0).Text)
'MessageBox.Show(str)
Dim con As System.Data.OleDb.OleDbConnection
Dim ds As New DataSet
Dim rea As System.Data.OleDb.OleDbDataReader
con = New OleDb.OleDbConnection
Dim da As New System.Data.OleDb.OleDbDataAdapter
con.ConnectionString = "Provider = Microsoft.ACE.OLEDB.12.0; Data Source= F:\Sowmya Laptop Backups\sowdb1.accdb;"
con.Open()
Dim cmd As OleDb.OleDbCommand = con.CreateCommand
cmd.CommandText = "UPDATE Casehistory set Prescription =' " & Presc.ToString() & "'"
rea = cmd.ExecuteReader
cmd.ExecuteNonQuery()
da.FillSchema(ds, SchemaType.Mapped)
da.Update(ds, "Casehistory")
con.Close()
Catch ex As Exception
Finally
End Try
End Sub
This code updates all the cells in that column. I want to update only the particular cell having Case_ID = str
Where I have to add the WHERE clause (WHERE Case_ID = " & str & "
I would use command parameters, neater and prevents the SQL injection issue. Something like:
cmd.CommandText = "UPDATE Casehistory set Prescription =#Presc WHERE Case_ID = #CaseID"
cmd.Parameters.AddWithValue("#Presc", Presc.ToString())
cmd.Parameters.AddWithValue("#CaseID",str)
As an aside, having all this code in the button click event is less than ideal. You might want to investigate structuring your app in a more maintainable way - perhaps with a Data Layer for example.
The Where clause should be appended to the end of the OleDbCommmand.CommandText, where you define the Update statement.