I am using sql server with my VB.NET application where in multiple instance of the application is run from different server (CITRIX). I am sorting and picking up one individual Row for processing and immediately marking that row as picked in a column so that other instance doesn't pick up the same row and waste time. The issue is, in between picking up the row and updating as picked, another instance of the application is picking up the row. I have been suggested for using with DB Lock but the concept is not that much clear to me like whether it will solve my problem, whether I need admin right to use it (I do not have admin right in client DB) etc. Below is the code snippet I have used.
Dim MyConnection As SqlConnection
Try
MyConnection = New SqlConnection(connString)
MyConnection.Open()
Dim tableName As String = myTableName
Dim sqlQuery As String = "Select Top 1 * from " + tableName + " where "<some condition>
Dim MyCommand As SqlDataAdapter = New SqlDataAdapter(sqlQuery, MyConnection)
Dim DS as DataSet = New DataSet
MyCommand.Fill(DS, tableName)
If DS.Tables(0).Rows.Count >= 1 Then
sqlQuery = "UPDATE " + tableName + " SET Fld = #fld where Cond1= '" + DS.Tables(0).Rows(0).Item("Cond1").ToString + "'"
Dim cmd As New Data.SqlClient.SqlCommand(sqlQuery)
cmd.CommandType = CommandType.Text
cmd.Parameters.Add("#fld", Data.SqlDbType.VarChar).Value = "Picked"
Try
cmd.Connection = MyConnection
cmd.ExecuteNonQuery()
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End If
Catch ex As Exception
MsgBox(ex.ToString)
Finally
MyConnection.Close()
End Try
I want it to make in such way that if an instance picks up a row, until it finishes updating the row, the row will not be visible to other instance with same query on the table, but other instance will continue to work with the other rows at the same time.
Two options I see:
Change your SELECT and UPDATE queries to a single UPDATE query. I didn't see where your SELECT was buying you anything.
If the SELECT is truly needed, then use a stored procedure on the database to handle the SELECT and the UPDATE on the database server side. You can lock the row during the transaction. See: Transaction Locking and Row Versioning Guide
Note that in general you should try to move your database queries to stored procedures. Not only does this reduce the amount of network traffic moving datasets back and forth, it increases the reliability, separates your database code from the UI, allows updates to the procedures without having to push new versions of the client application out and also avoids SQL injection.
Related
Here is my general understanding of database from what I read so far: Save / Update / Delete to pre-existing file made that binds to form thru SQL.
Here is what I am trying to do - I have a pre-made Data Table in Form with all columns defined. Once app is closed or certain functions ran, I need that data to be saved / updated in SQL (on local). Once app is open I need all that data to be preserved.
So far I have NOT found a single solution to it anywhere most refer to binding to an existing file. When I worked with Excel data transfer cells had to be defined and referenced in form for population.
My assumption is when a database from VB.NET is used, table with values can be created automatically saved/loaded/updated. However this is only my assumption since I never worked with SQL before. I am not sure if I need to manage an actual database file I created with all the values and then bind them to data table. For example DataTable cell XX to database column XX.
Here is what I done so far I have created database and added to my project. I tried few codes and I keep getting Dataset Empty even though there is Data in Table I tried to use DataTable as well but so far nothing has worked.
Please suggest on what I am doing wrong also additional information regards to databases will be great. As per previous I do know how binding works when actual file exist. But creating and managing is confusing to me since I keep thinking there should be a binding file.
Dim connetionString As String
Dim sqlCnn As SqlConnection
Dim sqlCmd As SqlCommand
Dim adapter As New SqlDataAdapter
Dim ds As New DataSet
Dim sql As String
connetionString = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Data_Ant.mdf;Integrated Security=True;Connect Timeout=30"
sql = "SELECT BN FROM DataTable" ' BN is my column name and DataTable is the name of my Table where data gets populated. This is also confusing to me How does it know which value is what? Is there are space/word/characters requirements?
' adapter.TableMappings.Add("DataTable", sql)
If ds.Tables.Count > 0 Then
sqlCnn = New SqlConnection(connetionString)
Try
sqlCnn.Open()
sqlCmd = New SqlCommand(sql, sqlCnn)
adapter.SelectCommand = sqlCmd
adapter.Update(ds)
adapter.Dispose()
sqlCmd.Dispose()
sqlCnn.Close()
Catch ex As Exception
MsgBox("Can not open connection !" & vbCrLf & Err.Description)
End Try
ElseIf ds.Tables.Count = 0 Then
MsgBox("Empty data")
End If
End Sub
Code I use to Create /Save Database. As per previous all columns/formats are pre-made, loaded.
Dim connetionString As String
Dim sqlCnn As SqlConnection
Dim sqlCmd As SqlCommand
Dim adapter As New SqlDataAdapter
Dim ds As New DataSet
Dim sql As String
connetionString = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Data_Ant.mdf;Integrated Security=True;Connect Timeout=30"
sql = "Select BN FROM DataTable"
adapter.TableMappings.Add("BN", sql)
If DataTable.RowCount > 0 Then
sqlCnn = New SqlConnection(connetionString)
Try
sqlCnn.Open()
sqlCmd = New SqlCommand(sql, sqlCnn)
adapter.SelectCommand = sqlCmd
adapter.Update(ds, "BN")
adapter.Dispose()
sqlCmd.Dispose()
sqlCnn.Close()
Catch ex As Exception
MsgBox("Can not open connection !" & vbCrLf & Err.Description)
End Try
ElseIf DataTable.RowCount = 0 Then
MsgBox("Empty data")
End If
End Sub
Please see more info below:
Data Table columns/format are structured for visual representation.
When User start the App Database can be empty/Can contain Values.
When users Runs certain function Closes App values are save and only values.
If I would you an MS Access I would structure same table/values and cross reference it with form values. Form Values come from outside source and Format/Qty is always known.
Hope this helps to have a cleaner look at my issue. Perhaps SQL is not a right choice for me? Does SQL needs to be build before value manipulation.
UPDATE: I Got rid of the Invalid Object error. Table had to be created 1st as I originally thought. However, My DataSet always comes up as EMPTY when I try to save... Cells do contain BN data as" 1,2, ....) Even if I to remove "If" logic Save and Load table comes out as empty. Something does load because when I try to ADD BN it tells me binding bla bla bla(different issue)
CODE:
Private Sub SaveData()
Dim connetionString As String = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Data_Ant.mdf;Integrated Security=True;Connect Timeout=30"
Dim sql As String = "SELECT BN FROM DataTable_d"
Dim sqlCnn As SqlConnection
Dim sqlCmd As SqlCommand
Dim adapter As New SqlDataAdapter
Dim ds As New DataSet()
adapter.TableMappings.Add("BN", sql)
If ds.Tables.Count > 0 Then
sqlCnn = New SqlConnection(connetionString)
Try
sqlCnn.Open()
sqlCmd = New SqlCommand(sql, sqlCnn)
adapter.SelectCommand = sqlCmd
adapter.Update(ds, "BN")
adapter.Dispose()
sqlCmd.Dispose()
sqlCnn.Close()
Catch ex As Exception
MsgBox("Can not open connection !" & vbCrLf & Err.Description)
End Try
ElseIf ds.Tables.Count = 0 Then
MsgBox("Empty data")
End If
End Sub
UPDATE: I got all the things working but I can't save multiple rows..... Could really use some help
In your SQL query remove WHERE DataTable ='. This statement is looking for a column name DataTable which I assume does not exist. The WHERE clause is used to help filter your query. You only use WHERE on column names in your table.
For instance:
SELECT BN FROM DataTable
will return all values from the BN column from DataTable.
Note that if you have multiple columns, the above query will still only return values from BN.
SELECT * FROM DataTable
will return every value in DataTable.
A helpful site to look at documentation for SQL is w3schools.
Let's start with just displaying some data. Add a DataGridView to a Form. You can call LoadData() from a button. I am not very sure of you connection string but give it a try.
Private dt As DataTable
Private sql As String = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Data_Ant.mdf;Integrated Security=True;Connect Timeout=30"
Private Sub LoadData()
'***EDIT*** Add instantiation line
dt = New DataTable()
'The Using...End Using blocks will close and dispose your database objects
'even if there is an error
Using cn As New SqlConnection(sql)
'You can pass the command text and the connection directly to the constructor
'In the select statement use the actual names of the field and table as they appear in the database.
Using cmd As New SqlCommand("Select BN From [Insert the name of the table in the database]", cn)
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
End Using
DataGridView1.DataSource = dt
End Sub
This is the simplest way I can think of to display data. We will proceed with changing the data once this works. If you get an error on cn.Open() We will have to work on the connection string.
****EDIT****
Private Sub TestConnection()
Dim sql As String = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Data_Ant.mdf;Integrated Security=True;Connect Timeout=30"
Using cn As New SqlConnection(sql)
cn.Open()
End Using
End Sub
I'm making a application with two database and want to insert my second database table with value from first database table they have same column but on different database. so i make a datatable to populate my data from first database table and try to insert it on my second database
so i make a datatable to populate my data from first database table and try to insert it on my second database using data from datatable but always error cause string value
Dim ds As DataSet = New DataSetMasBrgSpring
Dim dt As DataTable
dt = ds.Tables("DataTable1")
If DataGridView1.Rows.Count > 0 Then
dt.Rows.Clear()
For i = 0 To DataGridView1.Rows.Count - 1
dt.Rows.Add(DataGridView1.Rows(i).Cells(0).Value, etc..
Dim sql1 As String
Dim dataAdapter As New Data.SqlClient.SqlDataAdapter
Dim command As New Data.SqlClient.SqlCommand
command = "insert into MasbrgSpring (KODEC, WIRE, DIMENSION, STD, NOMLOT, STAT) VALUES (#kodec, #wire,#dimension,#std,#nomlot,#stat)"
command.Parameters.Add("#kodec", SqlDbType.VarChar)
etc...
For i As Integer = 0 To DataGridView1.Rows.Count - 1
command.Parameters(0).Value = DataGridView1.Rows(i).Cells(0).Value
command.Parameters(1).Value = DataGridView1.Rows(i).Cells(1).Value
etc...
str.Open()
COMMANDSQL(sql1)
str.Close()
Next
End If
End Sub
this is sub commandsql:
Public Sub COMMANDSQL(ByVal S As String)
sqlcom = New SqlCommand(S, str)
sqlcom.CommandType = CommandType.Text
sqlcom.ExecuteNonQuery()
End Sub
This is the error I get :
value of type string cannot be converted to 'system.data.sqlclient.sqlcommand'
There are many problems in your code. Of course the immediate one that triggers the compilation error is the fact that you use command instead of command.CommandText to assign the query to the command, but there are others.
If DataGridView1.Rows.Count > 0 Then
Dim command As New Data.SqlClient.SqlCommand
command.Text = "insert into MasbrgSpring
(KODEC, WIRE, DIMENSION, STD, NOMLOT, STAT)
VALUES (#kodec, #wire,#dimension,#std,#nomlot,#stat)"
command.Parameters.Add("#kodec", SqlDbType.VarChar)
.... add all the other parameters ....
' Don't forget to set the connection to the command
command.Connection = str
str.Open()
' Now loop over the rows and for each one execute the insert command
For i As Integer = 0 To DataGridView1.Rows.Count - 1
command.Parameters(0).Value = DataGridView1.Rows(i).Cells(0).Value
command.Parameters(1).Value = DataGridView1.Rows(i).Cells(1).Value
.....
command.ExecuteNonQuery()
Next
str.Close()
End If
End Sub
Here I have removed all the stuff about SqlDataAdapter, DataTable and DataSet. They are not needed at all when you execute directly a SqlCommand.
Finally the SqlCommand prepared in the loop is the one to be executed, if you create a new SqlCommand inside that SQLCOMMAND method then you need to give it the same info you have already given to the command used in the loop.
So there is no need also for SQLCOMMAND method but you can directly call ExecuteNonQuery on the prepared SqlCommand.
A final advice. It is a very bad programming practive to have a global SqlConnection object. It keeps resources locked on the client and on the server and if, for any reason, you get an exception, the connection remains open with side effects not immediately obvious when you get problems in other data code blocks.
ADO.NET has a Connection Pooling functionality far more advanced than the one you are trying to re-create keeping a global connection object. Instead use the Using statement around your Sql commands
Using sqlCon = New SqlConnection(......)
If DataGridView1.Rows.Count > 0 Then
Dim command As New Data.SqlClient.SqlCommand
command.Connection = sqlCon
..... the previous code....
End If
End Using
The using statement will help you to close and dispose the connection, while the connection pooling removes the overhead required to reconnect to the same database with the same connection string.
It's probably this line:
command = "insert into MasbrgSpring (KODEC, WIRE, DIMENSION, STD, NOMLOT, STAT) VALUES (#kodec, #wire,#dimension,#std,#nomlot,#stat)"
I think you mean:
command.CommandText = "insert into MasbrgSpring (KODEC, WIRE, DIMENSION, STD, NOMLOT, STAT) VALUES (#kodec, #wire,#dimension,#std,#nomlot,#stat)"
JUST A HEADS UP ----- This no longer applies for me. I fixed it by adding the following two lines to my form.load.
cb.QuotePrefix = "["
cb.QuoteSuffix = "]"
It has fixed the issue for me and I hope it sorts it out for you too.
Okay, so, I have an application in VB.net that serves as a scheduler for the trainers at the company I work at. In the edit mode (so updates can be made to the database the information is stored on) there are a number of buttons, adding and removing trainers, or adding weeks to the table.
The button causing me problems is the save/update button. It has three sets of commands within it, one for updating added columns, one for removed columns, and then a third one which simply updates other modified data. I know it probably could be more efficient but oh well, I'll get to that later.
The problem is, the last chunk of code includes "da.update(ds)" which is the data adapter updating the datasource. While this command works perfectly fine in our other app that connects to our SQL server, its causing problems here.
Any column where the first cell's value is null causes an exception saying
"Incorrect syntax near 'the column header's first two characters'."
Now, I thought this issue stemmed from - due to the exception - me using an incorrect set of names for the columns, which were the dates of the mondays of each week (so for example 01/02/2016) so it'd show Incorrect syntax near '01'. in this instance.
However, changing the naming convention did not fix this like how the exception would suggest, and it only occurs on columns where the FIRST value is a null - implying that the first trainer has nothing planned for this week right now.
Anyone have any ideas as to a way around this that doesnt involve basically filling in every null on this rather large table? I know that would work but It'd be pretty time consuming, and I am willing to do this if no other solution rears its head.
I've looked around on the internet and haven't found a solution that appeared relevant to our exact issue, so help would be very appreciated.
In case it is important - here is the function causing the issue.
Dim da As OleDbDataAdapter 'The datasets and adapters variables.
Dim da2 As OleDbDataAdapter
Public ds As DataSet = New DataSet
Public ds2 As DataSet = New DataSet
'Connection String. Connects to the server and finds the database and table listed.
cs = "Provider=SQLOLEDB;"
cs &= "Server=SOFWAREDEVSQLSE\SQLEXPRESS;"
cs &= "Database=MTS2;"
cs &= "User Id=;" 'You don't need to see that to be fair.
cs &= "Password=;" 'You don't need to see that to be fair.
sql = "Select * FROM MTS2;"
'Runs the string. Flares up a timed out error if connection could not be established.
Try
da = New OleDbDataAdapter(sql, cs)
da.Fill(ds)
da2 = New OleDbDataAdapter(sql, cs)
da2.Fill(ds2)
Catch ex As Exception
MsgBox("Connection failed. Please ensure you have a suitable connection to the Training network. Otherwise, refer to helpdesk support for further assistance.")
Me.Close()
End Try
dgvSchedule.DataSource = ds.Tables(0)
Private Function save()
'Try
''This section reads the SQL server for column names, and adds any that are listed in the DGV, but not the database. I know its a little messy but itll do.
Dim columnnum As Integer = -1
Dim columname As String
For Each column In ds.Tables(0).Columns
columnnum = columnnum + 1
columname = dgvSchedule.Columns(columnnum).HeaderText
If Not ds2.Tables(0).Columns.Contains(columname) Then
Dim SqlAddCol As String = "ALTER TABLE MTS2 ADD [" & columname.Trim() & "] nvarchar(255)"
Using con As New OleDbConnection(cs)
Using cmd As New OleDbCommand(SqlAddCol, con)
con.Open()
cmd.ExecuteNonQuery()
End Using
End Using
End If
Next
columnnum = -1
For Each column In ds2.Tables(0).Columns
columnnum = columnnum + 1
columname = ds2.Tables(0).Columns(columnnum).ColumnName
If Not ds.Tables(0).Columns.Contains(columname) Then
Dim SqlDelCol As String = "ALTER TABLE MTS2 DROP COLUMN [" & columname.Trim() & "]"
Using con As New OleDbConnection(cs)
Using cmd As New OleDbCommand(SqlDelCol, con)
con.Open()
cmd.ExecuteNonQuery()
End Using
End Using
End If
Next
ds2.Tables.Clear()
da2 = New OleDbDataAdapter(sql, cs)
da2.Fill(ds2)
da.Update(ds) ''''' The exception is thrown here. " Incorrect syntax near '01'."
DataTableColours()
MessageBox.Show("Data saved successfully. New weeks and trainers added and deleted. Changed values updated.")
'Catch
' MessageBox.Show("Data failed to update properly. Please ensure you are connected to the Baltic network and try again. If the problem persists, seek IT support.")
'End Try
End Function
The function saves the values in the data grid view (DGVSchedule) to the server by taking the current columns in the DS with their original columns (which are in DS2) A Sql query is then ran to add or remove any column mismatches. DS2 is then updated to use the same values as DS. Finally, DA.update(DS) is called, which updates all other modified values into the SQL server - theoretically. It is instead causing our peculiar exception.
Any help would be greatly appreciated, thanks.
I have fixed the problem I was encountering. I fixed it by adding the following two lines to my form.load.
cb.QuotePrefix = "["
cb.QuoteSuffix = "]"
Basically, I feel like a dumbass now but this solved the problem.
I have a project where I need to query a Teradata database and then copy the records returned to a SQL Server database. I can hit the Teradata db no problem and I can get the results into a DataTable. The SQL server db is already setup and has the same columns as the Teradata results (except for the auto id column). I am having trouble figuring out how to take the records in the DataTable and insert them into the SQL server db.
Here is what i have with some pseudo code where I didn't think the details were relevant:
Using cn As New TdConnection("User Id=XYZ12345;Password=XYZ12345;Data Source=teradataserver.company.com;Persist Security Info=False")
cn.Open()
Dim cmd As TdCommand = cn.CreateCommand()
'build the SELECT part of the command we will issue
cmd.CommandText = GetTeradataSqlString()
'setup the DataAdapter
Dim da As New TdDataAdapter(cmd)
' Provider specific types will be used in the data table
da.ReturnProviderSpecificTypes = False 'True=Use Teradata types, False=Use .NET types
' Adapter will determine how many statements will be batched
da.UpdateBatchSize = 0
Dim cb As New TdCommandBuilder(da)
'create a DataTable to hold our returned data
Dim dtCheck As New DataTable("TableCheck")
' Filling the data table with data retrieved from the select statement
da.Fill(dtCheck)
'create a DataSet to hold all of our tables
Dim dsMain As New DataSet("MainDataset")
'now we add the DataTable to our DataSet
dsMain.Tables.Add(dtCheck)
'at this point a cycle through the DataTable to the debug window shows we have the data we need from the Teradata db.
'now we will pump it into our SQL server database
Dim connSqlSvr As New System.Data.SqlClient.SqlConnection
connSqlSvr.ConnectionString = "Data Source=DestSqlServer;Initial Catalog=DestDb;Connect Timeout=15"
connSqlSvr.Open()
'now we create a SQL command to take the data in the Teradata DataTable and insert it into the SQL server table
Dim sqlCmd As New SqlCommand
With sqlCmd
.CommandType = CommandType.Text
Dim sbSqlCmd As New StringBuilder
sbSqlCmd.AppendLine("INSERT INTO [DestDb].[dbo].[Events] ([CityCode],[CarNum],[VIN],[Fleet],[EventItm])")
sbSqlCmd.AppendLine("SELECT City,CarNo,VIN,Fleet,EventDesc FROM #MyTable;")
.CommandText = sbSqlCmd.ToString
Dim sqlParam As New SqlParameter
sqlParam.ParameterName = "#MyTable"
sqlParam.SqlDbType = SqlDbType.Structured
sqlParam.Value = dtCheck
sqlParam.TypeName = "TableCheck"
.Parameters.Add(sqlParam)
.Connection = connSqlSvr
Dim rowsAffectedLoad As Integer = .ExecuteNonQuery()
debug.print(rowsAffectedLoad & " rows were loaded into the SQL server table.")
End With
'close and dispose the SQL server database connection
connSqlSvr.Close()
connSqlSvr.Dispose()
End Using
Running the code I get an exception:
"Column, parameter, or variable #MyTable. : Cannot find data type TableCheck."
I've looked for a method to insert a DataTable into a database and noticed many samples were using the INSERT INTO. I just dont think I am using the SqlParameter properly.
Your example appears to be using a Table Valued Parameter of type TableCheck but you have not defined that type within SQL Server. See http://msdn.microsoft.com/en-us/library/bb510489.aspx
CREATE TYPE LocationTableType AS TABLE
( LocationName VARCHAR(50)
, CostRate INT );
Although I can't guarantee that you can pass a TVP directly into a raw SQL statement.
I would actually suggest you use a different approach using SqlBulkCopy, http://msdn.microsoft.com/en-us/library/ex21zs8x(v=vs.110).aspx .
I had confusion with my code:
Dim sqladapter As SqlDataAdapter = New SqlDataAdapter()
Dim sqlcmd As SqlCommand = New SqlCommand()
sqlcmd = New SqlCommand("SELECT login, pass from Table1 where login=" & login.Text & "and pass='" & password.Text.ToString() & "';", connect)
Dim dr As SqlDataReader = sqlcmd.ExecuteReader()
Dim dt As DataTable = New DataTable()
dt.Load(dr)
If (dt.Rows.Count = 1) Then
'Display welcome page or do some action here.
Now, my question is, is there any other way of doing Rows.Count==1 . I'm feeling that it is very wrong and makes no sense at.
How do you verify from database that a user has only one valid record in table other than counting rows.
Thanks in Advance :)
(Please ask me before reporting question)
You have two problems, one is called Sql Injection and you have already numerous links that explain why is really bad. Another one is the plain text password stored in your database. This is a big security concern because everyone that has the possibility to look at your database could see the passwords of your users. (The gravity of this, of course, is linked to the nature of your application but cannot be downplayed) See this link for an answer on how to hash a string (a password) and get its encrypted version to store in the database instead of the plain text.
Finally the code you use could be changed to avoid both the SqlDataAdapter and the DataTable.
Just use an ExecuteScalar against an IF EXIST query that return just 1 if the user/password exists or zero if not
Dim cmdText = "IF EXISTS(SELECT 1 FROM Table1 WHERE login = #log AND pass = #pwd) " & _
"SELECT 1 ELSE SELECT 0"
using connect = new SqlConnection(connectionstring)
using sqlcmd = New SqlCommand(cmdText, connect)
connect.Open()
sqlcmd.Parameters.AddWithValue("#log", login.Text)
sqlcmd.Parameters.AddWithValue("#pwd", password.Text) ' <- Subst with a call to an hash function
Dim exists = Convert.ToInt32(sqlcmd.ExecuteScalar())
if exists = 1 Then
'Display welcome page or do some action
else
end if
End Using
End Using
There is only one way to answer to the question and its to count rows. The different solution would be to count them in database. For example you could write stored procedure that takes username and password and returns boolean this way you would drag less data.
As a side note there is potential sql injection in your code. You should not store clear password in database. You should return the whole row and match hash of the password from database to the hash of the paasword that you get from UI.