I've submitted a bunch of questions as of late - but this has been a great repository of information. I'm a .NET nub, as you can see, so if I'm missing basics or information please let me know and I'll try and fill in the gaps.
I'm using ASP.NET/VB.NET to create this with SQL 2005. I have a project where I'd like to take a set of records from a table, then send each one through an API, get a result and writeback the result to a table, then move to the next.
Initially, my thought was create a SQLDataSource that grabs all the records, then perform the action on a button to do the action of sending through each record.
Is there a way I can call the recordset from SQLDataSource and perform a loop? I'm thinking something like in Classic ASP/VBScript where you would open a RecordSet, do an action, then Loop until the RS was EoF.
Thanks for the help!
You can may want to put your results in a dataset. After getting the results, you can loop through the returned rows
Dim ds As Dataset = GetSomeDataFromSq
For Each dr As DataRow In ds.Tables(0).Rows
Console.WriteLine (dr("ColName"))
Next
You could also use a sqlDataReader
Using conn As sqlconnection = New sqlconnection("put conn info")
Using MyCommand As SqlCommand = New SqlCommand("SELECT ProductName FROM products", conn)
conn.Open()
Using myDataREader As SqlDataReader = MyCommand.ExecuteReader
While myDataREader.Read
Response.Write("Name: " & myDataREader.Item("ProductName"))
End While
End Using
End Using
End Using
Related
adding updating everything is fine even delete command is working but the strange part is after executing del command from vb.net application it swipes the position of EMPLOYEE_IDAND NAMEit shows normally in datagridviewafter adding or updating but specifically after deleting the record position of these to column changes until I stop the application and re run the entire project for debugging
Dim con As New MySqlConnection("server=localhost; user=root; password=Masoom1; database=airtech_db; convert zero datetime=true;")
Dim cmd As New MySqlCommand
Dim dt As New DataTable
Dim da As New MySqlDataAdapter
Dim sql As String
Dim DR As MySqlDataReader
Dim SQL_CMD_TXT As String
SQL_CMD_TXT = "DELETE FROM `employees` WHERE (`EMPLOYEE_ID` ='" &
EMPLOYEE_DEL_FRM.DEL_ID_TXT.Text & "'); SELECT * FROM `employees`;"
EMPLOYEE_DEL_FRM.Controls.Add(OBJECT_DATAGRIDVIEW)
With OBJECT_DATAGRIDVIEW
.Size = New Size(587, 242)
.Location = New Size(221, 171)
End With
Try
'DB CMD EXECUTION
con.Open()
With cmd
sql = SQL_CMD_TXT
.Connection = con
.CommandText = sql
End With
da.SelectCommand = cmd
da.Fill(dt)
'Command for datagridview object
With OBJECT_DATAGRIDVIEW
.DataSource = dt
'Scroll to the last row.
.Name = "MYDATAGRIDVIEW"
.FirstDisplayedScrollingRowIndex = .RowCount - 1
End With
con.Close()
Catch ex As Exception
Dim MEB = MessageBox.Show("ERROR FOR SQL CMD EXECUTION SECTION-" & ex.Message,
"SQL CMD EXECUTION", MessageBoxButtons.OK, MessageBoxIcon.Error)
Exit Sub
End Try
attaching the normal and after delete result in images
enter image description here
I am not sure I completely understood your problem, but your problem could that the datagridview generates the columns automatically. See: DataGridView.AutoGenerateColumns
Instead of doing SELECT * FROM is would better to select just the fields you need. If you add more fields to your table in the future, the columns in the datagridview may be displaced because they are in no particular order.
Rather than add the datagridview to your form at runtime:
EMPLOYEE_DEL_FRM.Controls.Add(OBJECT_DATAGRIDVIEW)
I would add it directly in the form layout (so you can see it at design time), and then customize it, bind each column to a database field. The appearance of the grid will be more predictable. Here is a small guide: How to bind datatable/list to datagridview with headers?
Relying on AutoGenerateColumns is not a great idea, because this will show all columns (usually not desirable) and not necessarily in the order that you want.
Other remarks:
Records can be edited or deleted directly in the datagridview, by simply selecting one or more rows, and pressing the Del key. Then just invoke the DataAdapter to commit the changes to the database. You should not even be doing DELETE FROM. Just let the user use the datagridview. The benefit is that if the user makes a mistake, you can roll back changes because you are using a datatable. Here you are deleting immediately and without warning.
Don't do stuff like:
SQL_CMD_TXT = "DELETE FROM `employees` WHERE (`EMPLOYEE_ID` ='" &
EMPLOYEE_DEL_FRM.DEL_ID_TXT.Text & "'); SELECT * FROM `employees`;"
Use parameterized queries instead, this code is insecure and will choke on single quotes or special characters (try it !). Here is a simple example: FAQ: How do I make a parameterized query in the database with VB.NET?. Please use parameterized queries from now on, don't develop bad habits that will always bite you sooner or later. The security risk alone is too high.
Also I am wondering why you did stacked queries. It would better to separate the SELECT from the DELETE.
In this code variable sql is not needed:
With cmd
sql = SQL_CMD_TXT
.Connection = con
.CommandText = sql
End With
Just use SQL_CMD_TXT directly. Otherwise it makes the code more difficult to follow.
I'm trying to take a Yes/No value from my database on Access and make it so if the Yes/No is checked on Access it will check it on the form. Although I keep getting
System.Data.OleDb.OleDbException: 'No value given for one or more required parameters.'
On the line Dim rs As OleDbDataReader = SQLCmd.ExecuteReader()
Sorry if it's a really easy and stupid mistake, I'm a college student and googling isn't helping me figure this one out.
cn.Open()
Dim SQLCmd As New OleDbCommand
SQLCmd.Connection = cn
SQLCmd.CommandText = "SELECT *, staffIn FROM Staff WHERE staffName = DarrenSloan"
Dim rs As OleDbDataReader = SQLCmd.ExecuteReader()
While rs.Read
Dim DisplayValue As String = rs("staffIn")
SQLCmd.Parameters.AddWithValue("#inorout", inOrOut.Checked)
SQLCmd.ExecuteNonQuery()
End While
cn.Close()
I know this is an old post but I seem to remember that OleDb does not support named parameters.
Also, pretty sure that DarrenSloan should be surrounded by single quotes, like any string value. And indeed, reusing the SQL command like this is not the way to do it.
The CommandText:
SQLCmd.CommandText = "SELECT *, staffIn FROM Staff WHERE staffName = DarrenSloan"
does not contain any parameter.
Thus, the parameter inorout has no effect:
SQLCmd.Parameters.AddWithValue("#inorout", inOrOut.Checked)
Either use two statements, one SELECT and one UPDATE.
Or use a different mechanism like a databound grid. Maybe you are using a datagridview control to display the data. Then there are different techniques to keep the data in sync. It depends on how you choose to render the data on your form.
Firstly, get rid of the loop. You would only use a loop if you were expecting more than one record. By the looks of it, you are expecting only one record, so no loop.
Secondly, stop calling ExecuteNonQuery. That is for making changes to the database, which you're obviously not trying to do. You obviously know how to get data from the query because you're doing it here:
Dim DisplayValue As String = rs("staffIn")
If you want to get data from another field, do the same thing. You can then use that data in whatever way you like, e.g.
Using connection As New OleDbConnection("connection string here"),
command As New OleDbCommand("SELECT * FROM Staff WHERE staffName = 'DarrenSloan'", connection)
connection.Open()
Using reader = command.ExecuteReader()
If reader.Read() Then
Dim inOrOut = reader.GetBoolean(reader.GetOrdinal("inorout"))
inOrOutCheckBox.Checked = inOrOut
End If
End Using
End Using
Notice that I have wrapped the text literal in the SQL in single-quotes? I would expect that you would normally not want to hard-code a name there, but use input from the user instead, In that case, you would use a parameter, e.g.
Using connection As New OleDbConnection("connection string here"),
command As New OleDbCommand("SELECT * FROM Staff WHERE staffName = #staffName", connection)
command.Parameters.Add("#staffName", OleDbType.VarChar, 50).Value = staffNameTextBox.Text
connection.Open()
Using reader = command.ExecuteReader()
If reader.Read() Then
Dim inOrOut = reader.GetBoolean(reader.GetOrdinal("inorout"))
inOrOutCheckBox.Checked = inOrOut
End If
End Using
End Using
I'm trying to display the sum total of a column in a access databse for a vb program. I've written the following code, but it doesn't do anything - the textbox is still on the default value when the program runs.
Dim command As OleDbCommand
Dim data_reader As OleDbDataReader
connection = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0; Data Source=H:\Computing\Year 13\Computing Project Course-work\Database41.accdb")
command = New OleDbCommand("SELECT SUM(Distance) As Int32 FROM [Table3];", Conn)
dr = command.ExecuteReader
While dr.Read
TextBox7.Text = dr.GetValue(4)
End While
You have only one column returned from that command.
You can't use try to read a value from column at index 4, it simply doesn't exist. And you should get an exception for this attempt. If you don't see the exception only means that you have somewhere an empty try/catch block that hides your error. You should use dr.GetValue(0) but giving the fact that you use a scalar function in your query (SUM) then it is better to use ExecuteScalar
Using connection = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0; Data Source=H:\Computing\Year 13\Computing Project Course-work\Database41.accdb")
Using command = New OleDbCommand("SELECT SUM(Distance) As Total FROM [Table3];", Conn)
Dim total = Convert.ToInt32(command.ExecuteScalar)
TextBox7.Text = total.ToString
End Using
End Using
(Notice that disposable objects like the connection, commands, and Readers should be disposed when you have finished to use them. The using block ensures this)
I am a complete beginner to .net and am confused at some basic things. Please help.
First of all the table I create and populate (by right clicking tables in server explorer) disappear once I restart the computer. how do I keep them.
Is there any better place/interface to type SQL queries in vb.net than the command prompt.
In the following code:
Dim cn As SqlConnection = New SqlConnection(strConnection)
cn.Open( )
' Create a data adapter object and set its SELECT command.
Dim strSelect As String = _
"SELECT * FROM Categories"
Dim da As SqlDataAdapter = New SqlDataAdapter(strSelect, cn)
' Load a data set.
Dim ds As DataSet = New DataSet( )
da.Fill(ds, "Categories")
This far the code runs fine but just to gain better understanding, I would like to ask that
while data from SQL Server database was saved into da in accordance to the query, why do we need to save/transfer it in the dataset object ds.
Is there any additional benefit of SqlCommand over SqlDataAdapter besides speed?
Dim autogen As New SqlCommandBuilder(da)
Dim dt As DataTable = ds.Tables("Categories")
' Modify one of the records.
Dim row As DataRow = dt.Select("CategoryName = 'Dairy Products'")(0)
row("Description") = "Milk and stuff"
gives an error when I use it with
da.Update(ds, "Categories")
regarding dt.select not returning any value.
What is the way out?
to answer your questions :
The tables you create with the server explorer are IN MEMORY. Same goes for dataset, they are in-memory representation of your table. As for your 2nd example, the DS you use isnt filled when you try to get the DT. hence why the DT is empty.
If your starting, I would suggest you go look into Linq-to-Sql (http://msdn.microsoft.com/en-us/library/bb425822.aspx) for a more up-to-date way of doing sql in .net ( I think its 4.0 framework)
As for the 2nd point, I'd say normally you should use store procedure for most of your sql commands .. the sqlcommand is use like this
Try
Cmd = New SqlClient.SqlCommand("st_InventoryStatus_Or_AnyStoreProcName_Or_ASqlQuery")
Cmd.CommandTimeout = 300 'not really needed'
Cmd.CommandType = CommandType.StoredProcedure 'you can type CommandType.Text here to use directly your "Select * from Category"'
Cmd.Parameters.Clear() 'just to be sure its empty, its not mandatory'
Cmd.Parameters.Add("#idCategory", SqlDbType.Int).Value = myCategory.Id 'here are the parameters of your store proc, or of your query ("select * from Category where Category.id = #Id")'
Catch ex As Exception
MsgBox(ex.Message, MsgBoxStyle.Information)
End Try
Scenario is this; I've a sqldatareader query that seems to be returning nothing when I try to convert the sqldatareader to a datatable using datatable.load.
So I debug into it, I grab the verbose SQL query before it goes into the sqldatareader, just to make sure it's formatted correctly. I copy and paste this into SQL server to run it and see if it returns anything. It does, one row.
I go back to visual studio and let the program continue, I create a datatable and try to load the sqldatareader but it just returns an empty reader. I'm baffled as to what's going on.
I'll copy a version of the code (not the exact SQL query I'm using but close) here:
Dim cn As New SqlConnection
cn.ConnectionString = <connection string details here>
cn.Open()
Dim sqlQuery As String = "select * from Products where productid = 5"
Dim cm As New SqlCommand(sqlQuery, cn)
Dim dr As SqlDataReader = cm.ExecuteReader()
Dim dt as new DataTable
dt.load(dr)
dt should have contents but it's empty. If I copy that SQL query into sql server and run it I get a row of results.
Any ideas what I'm doing wrong?
######### UPDATE ############
I've now noticed that it seems to be returning one less row than I get with each SQL query. So, if I run the SQL myself and get 1 row then the datatable seems to have 0 rows. If the query returns 4 rows, the datatable has 3!! Very strange, any ideas anyone?
######### FURTHER UPDATE ############
Ok I've done a loop to count the rows of the datareader before using the datatable.load method. In my test query I'm getting 4 rows (the correct amount) in the datareader, as soon as I use the datatable.load method it says the datatable is empty, what's going on?!
###### Ok
So it seems a datareader is a one-way thing, iterate through it to get the row count and it's essentially empty as far as any other bit of code is concerned. Didn't realise it was forward only and wouldn't 'reset' once read through.
Insert this line above dt.load(dr), check the value in your debug window:
Debug.WriteLine("Datareader has rows: " & dr.HasRows)
Also make sure your connection gets closed by changing cm.ExecuteReader() to :
cm.ExecuteReader(CommandBehavior.CloseConnection);