very new to VB so apologies if I don't make a lot of sense.
I have a database of trivia questions with three fields: Question, Answer and Times Asked.
I want to be able to hit a button and receive a question from the database at random from among the records with the lowest Times Asked value, then add one to that record's Times Asked value.
Can anyone help me out? Here's what I've got so far:
Private DBCon As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0; "Data Source=Trivia.accdb;")
Public Sub GenerateQuestion()
DBCon.Open()
'grab how many questions there are total
Dim QuestionsQuery As String = "SELECT COUNT(*) FROM Questions"
Dim QuestionsCmd As New OleDbCommand(QuestionsQuery, DBCon)
Dim NumOfQuestions As Integer = QuestionsCmd.ExecuteScalar()
'grab the lowest number from Times Asked
Dim SeenQuery As String = "SELECT MIN(`Times`) FROM Questions"
Dim SeenCmd As New OleDbCommand(SeenQuery, DBCon)
Dim SeenReader As OleDb.OleDbDataReader = SeenCmd.ExecuteReader
SeenReader.Close()
End Sub
This sub is called from a button on another form and when I click the button I get an exception for no data existing in the row/column. Even if I manage to get this value though I have no idea what the next step is with actually grabbing a random question from among the minimum Times values and adding one to the Times value for that question.
For reference here is the table I'm working with atm:
http://i.imgur.com/2vwlVQR.jpg
EDIT: To anyone finding this in the future here is the code that fixed the problem:
Imports System.Data.OleDb
Dim rng As New Random
Dim connection As OleDb.OleDbConnection
Private Function GetQuestionWithAnswer() As Tuple(Of String, String)
'Use XML literals for the SQL statements.
Dim selectSql = <sql>
SELECT *
FROM Questions
WHERE Times =
(
SELECT MIN(Times)
FROM Questions
)
</sql>
Dim updateSql = <sql>
UPDATE Questions
SET Times = #Times
WHERE ID = #ID
</sql>
Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0; Data Source=Trivia.accdb;")
Dim adapter As New OleDbDataAdapter(selectSql.Value, connection)
Dim updateCommand = New OleDbCommand(updateSql.Value, connection)
With updateCommand.Parameters
.Add("#Times", OleDbType.Integer, 0, "Times")
.Add("#ID", OleDbType.Integer, 0, "ID")
End With
adapter.UpdateCommand = updateCommand
Dim table As New DataTable
'Getall the questions that have been asked the fewest number of times.
adapter.Fill(table)
'Select a question at random.
Dim record = table.Rows(rng.Next(table.Rows.Count))
'Increment the number of times the question has been asked and save the change.
record("Times") = CInt(record("Times")) + 1
adapter.Update(table)
'Package up the selected question.
LblQuestion.Text = record(1)
Return Tuple.Create(CStr(record("Question")), CStr(record("Answer")))
End Using
End Function
Here you can find the use of Rand in Mysql:http://jan.kneschke.de/projects/mysql/order-by-rand/
If you use Rand, it is not necessary to Select questions which are not shown mostly. It will be balanced if you use only Rand.
Related
I have data shown in DataGridView. I made a Button when selecting IDs in the grid the code below runs but I keep getting an error.
Dim cnx As New MySqlConnection("datasource=localhost;database=bdgeststock;username=root;password=")
Dim cmd As MySqlCommand = cnx.CreateCommand
Dim resultat As Integer
If ConnectionState.Open Then
cnx.Close()
End If
cnx.Open()
If grid.SelectedCells.Count = 0 Then
MessageBox.Show("please select the ids that u want to delete")
Else
cmd.CommandText = "delete from utilisateur where idu= #P1"
cmd.Parameters.AddWithValue("#P1", grid.SelectedCells)
resultat = cmd.ExecuteNonQuery
If (resultat = 0) Then
MessageBox.Show("error")
Else
MessageBox.Show("success")
End If
End If
cnx.Close()
cmd.Dispose()
How does this make sense?
cmd.Parameters.AddWithValue("#P1", grid.SelectedCells)
As you tagged this question WinForms, you are presumably using a DataGridView rather than a DataGrid (names matter so use the right ones). In that case, the SelectedCells property is type DataGridViewSelectedCellCollection. How does it make sense to set your parameter value to that? How is that going to get compared to an ID in the database?
If you expect to use the values in those cells then you have to actually get those values out. You also need to decide whether you're going to use a single value or multiple. You are using = in your SQL query so that means only a single value is supported. If you want to use multiple values then you would need to use IN and provide a list, but that also means using multiple parameters. I wrote an example of this type of thing using a ListBox some time ago. You can find that here. You could adapt that code to your scenario like so:
Dim connection As New SqlConnection("connection string here")
Dim command As New SqlCommand
Dim query As New StringBuilder("DELETE FROM utilisateur")
Select Case grid.SelectedCells.Count
Case 1
query.Append(" WHERE idu = #idu")
command.Parameters.AddWithValue("#idu", grid.SelectedCells(0).Value)
Case Is > 1
query.Append(" WHERE idu IN (")
Dim paramName As String
For index As Integer = 0 To grid.SelectedCells.Count - 1 Step 1
paramName = "#idu" & index
If index > 0 Then
query.Append(", ")
End If
query.Append(paramName)
command.Parameters.AddWithValue(paramName, grid.SelectedCells(index).Value)
Next index
query.Append(")")
End Select
command.CommandText = query.ToString()
command.Connection = connection
SelectedCells is a collection of cells
so it never can be only one id, so you have to guess which was you want or only allow one row to be selected
grid.SelectedCells(0).Value.ToString()
Or you have to program a loop to delete all selected rows
I want to be able to read a value (in this case an Group ID). All the topics and tutorials I've watched/read take the data and put it into a textbox.
I don't want to put it in a textbox in this case; I want to grab the Group ID and then say:
If Group ID = 4 then login
Here is an image of the database.
Basically, but none of the tutorials I watch or the multiple forums. None of them take a a value and say if value = 4 then login or do something else.
If text = "1" Then
MysqlConn = New MySqlConnection
MysqlConn.ConnectionString =
"server='ip of server'.; username=; password=; database="
Dim READER As MySqlDataReader
Dim member_group_id As String
Try
MysqlConn.Open()
Dim Query As String
Query = "SELECT * FROM `core_members` where name='" & TextBox2.Text & "'"
Query = "SELECT * FROM `nexus_licensekeys` where lkey_key='" & TextBox1.Text & "'"
COMMAND = New MySqlCommand(Query, MysqlConn)
READER = COMMAND.ExecuteReader
Dim count As Integer
count = 0
While READER.Read
count = count + 1
End While
Here is what I have so far. I'm kind of new implementing mysql data with visual basic and only recently started to get into it. I'm not sure what comes next or how to even start with reading the group id etc.
As I said any help from here on out would be highly appreciated of how to read the group id and say if this group id = this number then do this or that. I'm sure you get the idea.
I divided the code into UI Sub, and Data Access Function that can return data to the UI. Your Event procedure code should be rather brief and the functions should have a single purpose.
Keep your database objects local to the method. This way you can have better control. The Using...End Using blocks ensure that your database objects are closed and disposed even if there is an error.
I leave it to you to add validation code. Checking for empty TextBox or no return of records.
I hope this serves as a quick introduction to using ADO.net. The take away is:
Use Parameters
Make sure connections are closed. (Using blocks)
Private ConnString As String = "server=ip of server; username=; password=; database="
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim GroupID As String = GetGroupID(TextBox1.Text)
If GroupID = "4" Then
'your code here
End If
Dim LocalTable As DataTable = GetLicenseKeysData(TextBox1.Text)
'Get the count
Dim RowCount As Integer = LocalTable.Rows.Count
'Display the data
DataGridView1.DataSource = LocalTable
End Sub
Private Function GetGroupID(InputName As String) As String
'Are you sure member_group_id is a String? Sure looks like it should be an Integer
Dim member_group_id As String = ""
'You can pass the connection string directly to the constructor of the connection
Using MysqlConn As New MySqlConnection(ConnString)
'If you only need the value of one field Select just the field not *
'ALWAYS use parameters. See comment by #djv concerning drop table
Using cmd As New MySqlCommand("SELECT g_id FROM core_members where name= #Name")
'The parameters are interperted by the server as a value and not executable code
'so even if a malicious user entered "drop table" it would not be executed.
cmd.Parameters.Add("#Name", MySqlDbType.VarChar).Value = InputName
MysqlConn.Open()
'ExecuteScalar returns the first column of the first row of the result set
member_group_id = cmd.ExecuteScalar.ToString
End Using
End Using
Return member_group_id
End Function
Private Function GetLicenseKeysData(InputName As String) As DataTable
Dim dt As New DataTable
Using cn As New MySqlConnection(ConnString)
Using cmd As New MySqlCommand("SELECT * FROM `nexus_licensekeys` where lkey_key= #Name;", cn)
cmd.Parameters.Add("#Name", MySqlDbType.VarChar).Value = InputName
cn.Open()
dt.Load(cmd.ExecuteReader())
End Using
End Using
Return dt
End Function
Is there a way to make populating ListBox fast, because the UI is freezing on form load upon populating the ListBox?
This is my form load code:
Dim abc As String = itemCount()
Dim output = Account_Get(a)
For Each s In output
ListBox1.Items.Add(s)
count1 += 1
If count1 = abc Then
ListBox1.Visible = True
End If
Next
This is the query in module:
Public Function Account_Get(ByVal chk As String) As List(Of String)
Dim result = New List(Of String)()
Try
cn.Open()
sql = "select column_name as str from table where status = 'New' order by rand()"
cmd = New MySqlCommand(sql, cn)
dr = cmd.ExecuteReader
While dr.Read
result.Add(dr("str").ToString())
End While
Return result
Catch ex As Exception
MsgErr(ex.Message, "Error Encounter")
Return Nothing
Finally
cn.Close()
End Try
End Function
this is working fine. but the fact that it loads too many datas. the ui is freezing on load. hoping someone could help me with this. thanks!
Since you are incrementing count1 I assume it is some sort of number. However, you are then comparing it to a string in the If statement. Please use Option Strict.
Changed the Function to return an Array of String. Took the random sort form the sql statement and moved it to a little linq at the end or the function.
You could add a Stopwatch to the data retrieval and the display sections to see where your bottleneck is. BeginUpdate and EndUpdate on the listbox prevents repainting on every addition.
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim output = Account_Get()
ListBox2.BeginUpdate()
ListBox2.Items.AddRange(output)
ListBox2.EndUpdate()
End Sub
Private Rand As New Random
Public Function Account_Get() As String()
Dim dt As New DataTable
Dim result As String()
Using cn As New MySqlConnection("Your connection string")
Dim Sql = "select column_name as str from table where status = 'New'" 'order by rand()"
Using cmd = New MySqlCommand(Sql, cn)
Try
cn.Open()
dt.Load(cmd.ExecuteReader)
Catch ex As Exception
MessageBox.Show(ex.Message, "Error Encounter")
Return Nothing
End Try
End Using
End Using
result = (From dRow In dt.AsEnumerable()
Let field = dRow("str").ToString
Order By Rand.Next
Select field).ToArray
Return result
End Function
The query you are using contains a random order. Ordering records randomly can be a huge performance issue within MySQL as it has to go through all records in the table and then sort them randomly. The more records in the table, the bigger the performance penalty. There is also no limitation on the number of records in your query. So if there are thousands of items in your table the listbox will also be thousands of items in size, which could also take a long time.
If you really require the random ordering you could do something about it in your code. I'm now assuming here that you are: 1) using identifiers in your table, 2) you actually wish to limit the number of items in your listbox and not display all of them.
Get a grasp of the total number of records in the table by a query
Pick a random number from the range of items in your table
Fetch the nearest record
Hope this helps you to get going to find a solution
I am trying to populate a set of textboxes from a combobox on a form. The combo box is populated using a dataset when the form loads. When this is loaded it needs to show only one entry per unit number in the kitcombobox (which is a unit number for a kit with multiple pieces of equipment in it) but display the multiple pieces of equipment's information in the different text boxes when the unit number is selected via the kitcombobox. What approach should I take towards this? I'm really lost and this is all I have so far :(
Private Sub ckunit()
Dim ds As New DataSet
Dim cs As String = My.Settings.MacroQualityConnectionString
Dim kitcombobox As String = "SELECT DISTINCT Unit_Number, Status FROM Calibrated_Equipment WHERE CHARINDEX('CK', Unit_Number) > 0 AND Status='" & ckstatuscombbx.Text & "'"
Dim sqlconnect As New SqlConnection(cs)
Dim da As New SqlDataAdapter(kitcombobox, sqlconnect)
sqlconnect.Open()
da.Fill(ds, "Calibrated_Equipment")
sqlconnect.Close()
kitcombbx.DataSource = ds.Tables(0)
End Sub
Assuming you are using WinForms, I think the key will be adding an event handler for the SelectionChangedCommitted event on kitcombbx.
You can then checked the properties on the combobox to check what is selected and run another query to pull equipment information for that kit. It'd probably look something like this:
Private Sub kitcombbx_SelectionChangeCommitted(sender As Object, e As EventArgs) _
Handles kitcombbx.SelectionChangeCommitted
Dim kit = kitcombbx.SelectedItem.ToString()
Dim kitEquipment = FetchKitEquipmentInformation(kit)
PopulateEquipmentInformation(kitEquipment)
End Sub
The way you're currently constructing your query (by concatenating string parameters directly from user input) results in bad performance for most database systems, and moreover, is a huge security vulnerability. Look up SQL injection for more detail (or read these two questions).
Better DB code would probably look something like this:
Dim query = New StringBuilder()
query.AppendLine("SELECT DISTINCT Unit_Number, Status ")
query.AppendLine("FROM Calibrated_Equipment ")
query.AppendLine("WHERE CHARINDEX('CK', Unit_Number) > 0 ")
query.AppendLine(" AND Status = #STATUS ")
Dim connection As New SqlConnection(My.Settings.MacroQualityConnectionString)
Dim command As New SqlCommand(query, connection);
command.Parameters.Add("#STATUS", ckstatuscombbx.Text);
Dim da As New SqlDataAdapter(kitcombobox, sqlconnect)
'And so on...
Your question is a bit broad (and therefore, likely off-topic for StackOverflow), see How to Ask.
I am making a CMS portal for my company which will fetch records from SQL server using ASP.NET:
My problem is that when I fetch values it only shows the last one. But my need is that it should display one by one values with say 5-10 seconds gap in between here is my code:
Imports System
Imports System.Data.Sql
Imports System.Data.SqlClient
Partial Class _Default
Inherits System.Web.UI.Page
Dim connectionString As String = "Data Source=soemserv;Initial Catalog=data;User Id=master; Password=hushotn;"
Dim conn As New SqlConnection(connectionString)
Public Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
conn.Open()
Dim comm As New SqlCommand("select Queue,[Timing(IST)],[Status at],TAT,[Staffing at] from DTD_LCD_Queue_Status", conn)
Dim reader As SqlDataReader = comm.ExecuteReader
While reader.Read()
lblQueueName.Text = reader("Queue").ToString.Trim
lblTimingIST.Text = reader("Timing(IST)").ToString.Trim
lblStatusAt.Text = reader("Status at").ToString.Trim
lblTAT.Text = reader("TAT").ToString.Trim
lblStaffingAt.Text = reader("Staffing at").ToString.Trim
End While
End Sub
End Class
How do I loop though each record I tried Do and Loop but its not working...
Thanks in advance!
EDIT
One Step Ahead with no LUCK!!!!
I have written this code but still getting the last row only
For I As Integer = 0 To 15
lblTemp.Text = I.ToString
Dim comm As New SqlCommand("select Queue,[Timing(IST)],[Status at],TAT,[Staffing at] from DTD_LCD_Queue_Status where SrNo='" + lblTemp.Text + "';", conn)
Dim reader As SqlDataReader = comm.ExecuteReader
While reader.Read()
lblQueueName.Text = reader("Queue").ToString.Trim
lblTimingIST.Text = reader("Timing(IST)").ToString.Trim
lblStatusAt.Text = reader("Status at").ToString.Trim
lblTAT.Text = reader("TAT").ToString.Trim
lblStaffingAt.Text = reader("Staffing at").ToString.Trim
Thread.Sleep(2000)
End While
Next
Note I have dynamically given rows i.e 0 to 15
Please guide me!!
Only the last values are printed because : you are fetching a group of rows(data) through the readr and in first iteration of the while loop the first rows(data) are copied to the controls then for the second iteration the contents in the controls are over written with the second row. This will happens in each iteration hence only the last data are displayed.
- This can be avoided by using
Group of controls which are dynamically created(but not practical and good)
using DataGridView(grid) to display the items How to do this
**The method you ware suggested (using Timer) is also possible but it is not a good programming practice only the last values ware displayed all the others flashed for a duration of 5-10 seconds **