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
Related
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 have the following code that tries to get records from two different tables and then add them to the particular comboboxes. Only the first query works and the second one is ignored.
Try
sqlConn = New MySqlConnection
connStr = New String("Server = localhost; Database = gen_database; Uid = root; Pwd =")
sqlConn.ConnectionString = connStr
myCommand = New MySqlCommand("Select DevCompanyName from developer_name_table; Select DevType from development_type_table")
myCommand.CommandType = CommandType.Text
myCommand.Connection = sqlConn
ComboBox1.Items.Clear()
sqlConn.Open()
MsgBox("Connection Open.")
dR = myCommand.ExecuteReader()
Do While dR.Read()
ComboBox1.Items.Add(dR("DevCompanyName"))
ComboBox2.Items.Add(dR("DevType")) 'Error shows here Could not find specified column in results: DevType
Loop
Catch ex As MySqlException
MsgBox(ex.ToString)
Finally
dR.Close()
sqlConn.Close()
End Try
I can think of another way which is to do it in multiple query but can the code be simplified to something like this?
Using a DBDataReader with 2 queries, only only the first executes because there is no way to signal which table/query each read item is from. Your "double read" loop seems to assume they will be returned at the same time (rather than one query after the other - the same way they are sent to the DBCOmmand); if it did work that way, it would fail whenever there are not the same number of rows in each table.
Using DataTables affords you the chance to simply bind the result to your combos rather than copying data into them:
Dim SQL = "SELECT * FROM Sample; SELECT * FROM Simple"
Dim ds As New DataSet
Using dbcon As New MySqlConnection(MySQLConnStr),
cmd As New MySqlCommand(SQL, dbcon)
dbcon.Open()
Dim da As New MySqlDataAdapter(cmd)
da.Fill(ds)
End Using
' debug results
Console.WriteLine(ds.Tables.Count)
Console.WriteLine(ds.Tables(0).Rows.Count)
Console.WriteLine(ds.Tables(1).Rows.Count)
If I look at the output window, it will print 2 (tables), 10000 (rows in T(0)) and 6 (rows in T(1)). Not all DBProviders have this capability. Access for instance will choke on the SQL string. Other changes to the way your code is composed:
DBConnections and DBCommand objects need to be disposed. They allocate resources, so they need to be created, used and disposed to release those resources.
The Using block does that for us: The target objects are created at the start and closed and disposed at End Using.
The code above stacks or combines 2 such blocks.
The code fills a DataSet from the query, in this case creating 2 tables. Rather than copying the data from one container to another (like a control), you can use a DataTable as the DataSource:
cboDevName.DataSource = ds.Tables(0)
cboDevName.DisplayMember = "DevName" ' column names
cboDevName.ValueMember = "Id"
cboDevType.DataSource = ds.Tables(1)
cboDevType.DisplayMember = "DevType"
cboDevType.ValueMember = "DevCode"
The result will be all the rows from each table appearing in the respective combo control. Typically with this type of thing, you would want the ID/PK and the name which is meaningful to the user in the query. The user sees the friendly name (DisplayMember), which the code can easily access the unique identifier for the selection (ValueMember).
When using bound list controls, rather than using SelectedIndex and the SelectedIndexChanged event, you'd use SelectedValue and SelectedItem to access the actual data.
MSDN: Using Statement (Visual Basic)
You can use .net connector (download here)
Then you can install it and add it to your project (project -> references -> add -> browse).
Finally add import:
Imports MySql.Data.MySqlClient
So you'll be able to use this:
Dim connStr as String = "Server = localhost; Database = gen_database; Uid = root; Pwd ="
Dim SqlStr as String = "Select DevCompanyName from developer_name_table; Select DevType from development_type_table"
Dim ds As DataSet = MySqlHelper.ExecuteDataset(CnStr, SqlStr)
ds will contain two datatables: one for each query
How to create receipt number like this "BSP000001" and in the next load of the receipt form, the receipt number will be "BSP000002" and save again to database..I'm using vb2010 and MySql database...It is just like auto increment receipt number in my database table.
And I really don't know how to make it.
It looks like this to my transaction table and I want show for Receipt_No column only, just to figure out..
Receipt_No
BSP000001
BSP000002
BSP000003
badly needed your help, to anyone who read this post...Big Please for Mr and Mrs Programmers outside the world..I Thankyou..
In a single user scenario, usually you could use the MAX function or order your receipts in DESCENDING order to find the last inserted one. Once you have this last record it is easy to extract the numeric part, increase the value by one and build the new receipt_no
Function GetNewReceiptNumber(prefix as string ) as String
using cn = new MySqlConnection(connectionstring)
using cmd = cn.CreateCommand()
cn.Open()
cmd.CommandText = "select receipt_no from receipts order by receipt_no DESC limit 1"
Dim result = cmd.ExecuteScalar
if result IsNot DbNull.Value AndAlso result IsNot Nothing Then
Dim number = Convert.ToInt32(result.ToString().SubString(prefix.Length))
return prefix & (number + 1).ToString("D6")
else
return prefix & "000001"
End If
End Using
End Using
End Function
or perhaps it is better to use MAX(receipt_no) for a slightly faster performance (but you really need to have an index of receipt_no)
cmd.CommandText = "select MAX(receipt_no) from receipts"
You could call this method from the code that tries to insert a new receipt in this way
Dim newReceiptNumber = GetNewReceiptNumber("BSP")
In this answer there are some assumptions:
You have a global variable that keeps the details of your connection
string to MySql called connectionstring
The name of the table where you store the receipts is called
receipts
My problem is, when I query by a usual ID, like number with no segments = 1234567890, it works nicely.
But I need to query by some kind of segmented values or ID as = 123-4567-890, when I try by 123-4567-890 this id it does not query anything in mysql although in the database this 123-4567-890 ID is present.
So what is the possible solution to search by segmented value in mysql in VB.NET
Here is below, my trying codes in vb
Public Sub student()
textbox1.text= "123-4567-890"
Try
dbConn()
Dim myAdapter As New MySqlDataAdapter("Select studentID, batchID, studentStatus from student where studentID= " & textbox1.text, ServerString)
Dim myDataTable As New DataTable
myAdapter.Fill(myDataTable)
If myDataTable.Rows.Count > 0 Then
vrSID = myDataTable.Rows(0).Item("studentID")
vrRecBatchID = myDataTable.Rows(0).Item("batchID")
vrAttendanceStatus = myDataTable.Rows(0).Item("studentStatus")
If vrSID = vrIDD Then
If vrAttendanceStatus = "Active" Then
Console.Beep()
batchRoutine()
Else
led3()
Console.Beep()
End If
End If
Else
Console.Beep()
teacher()
End If
Catch ex As Exception
Console.Beep()
MsgBox ("Error")
End Try
End Sub
When you are running into problems, the easiest way to solve them is to break things down to the simplest scenario. So instead of complicating things with table adapters and data tables, see what happens when you just send MySQL the query you 'think' works correctly.
So start out by seeing if you can get this to work, then go from there:
Dim sql As String = "select id from mytable where id = '123-4567-890'"
Using cnx As New MySqlConnection("connection_string")
Using cmd As New MySqlCommand(sql, cnx)
cnx.Open()
Using reader As MySqlDataReader = cmd.ExecuteReader()
Debug.Assert(reader.Read(), "No results")
Trace.WriteLine(reader.GetValue(reader.Item(0)))
End Using
End Using
End Using
if the column is in-fact a sort of student ID column (not social security I would expect), and the table has it without special characters, I would pre-strip the extra formatting (hyphens) from the string and pass the CLEANED value to the query as a parameter to get results.
Also, by explicitly adding the query string Plus the text box value, you are leaving yourself WIDE OPEN to sql injection. Look into Parameterized queries (my guess is it would be an object something like MySqlDataParameter data type.)