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Pete O'Hanlon wrote: That really depends on how you set up the reader.
True, but the question was about the disconnected architecture. Whether one closes the connection (and the reader) doesn't change the principles.
Yes, it depends a bit on the reader, it might have been initialized with the argument to close the connection once the reading is done. You might also want to keep an open connection for a second command that gets executed, but the idea behind the disconnected architecture is to close the connection when you're done.
That depends on the programmer, and is a best practice again. It's not mandatory, you can open a single connection for your app and keep it open for the lifetime of the application. I'd rather see it closed, or better yet, encapsulated with a USING statement.
I are Troll 
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In that one case, no, it's not disconnected. In other cases, where a dataset is returned or some other operation, yes, it is.
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Dave Kreskowiak wrote: where a dataset is returned
DataAdapters use DataReaders -- but they're smart enough to open and close the connection as necessary.
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Dear All,
Thanks for this discussion.
Regards,
Amol
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PIEBALDconsult wrote: DataAdapters
Which work with DataSet/DataTables... 
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Do you know of another means of retrieving data that does not involve a connection to the database at some point?
I know the language. I've read a book. - _Madmatt
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Sounds like a data input requirement I had a while back.
"The data must be entered into the database without using an import process, nor any keyboard interaction"
I was thinking, voice recognition, or maybe psychic powers.
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Amolravatale wrote: ADO.NET is disconnected architecture
IMO, depends on how ADO.Net is implemented really.
The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.
My latest tip/trick
Visit the Hindi forum here.
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Having a disconnected architecture does not have anything to do with which objects require shorter or longer connection time. You need to first understand the basic principle and definition od a disconnected architecture.
In traditional data access components, you make a connection to the database system and then interact with it through SQL queries using the connection. The application stays connected to the DB system even when it is not using DB services. This commonly wastes the valuable and expensive database resource as most of the time applications only query and view the persistent data. ADO.Net solves this problem by managing a local buffer of persistent data (data set). Your application automatically connects to the database server when it needs to pass some query and then disconnects immediately after getting the result back and storing it in dataset. This design is very much similar to the connection less services of http over the internet. It should be noted that ADO.Net also provides the connection oriented traditional data access services.
Another important aspect of the disconnected architecture is that it maintains the local repository of data in the dataset object. The dataset object stores the tables, their relationship and different constraints. The user performs operations like update, insert, delete to this dataset locally and finally the changed dataset is stored in actual database as a batch when needed. This greatly reduces the network traffic and results in the better performance.
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Arjun Bahree (TechnoMatrix) wrote: The user performs operations like update, insert, delete to this dataset locally and finally
... the application crashes and all the changes are lost. 
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Connect when you need access. Disconnect when you don't.
When using a DataReader or performing a sequence of operations within a transaction, you need access.
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I created org chart using trial version in C#.net dynamically using mysql database, it is running only in localhost. If i want to run IIS it is giving message like u have to purchase and i am not able to view that chart. Is there any alternation solution to view that chart and it can run in IIS server. If anybody knows please reply me. Thanks in advance.
modified on Friday, September 10, 2010 12:57 AM
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You could consider supporting the devs who wrote the tool and buy the damn thing. 
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I appreciate that we have some clever people here in the forums, but even they need some help now and again. How about clarifying some points, such as what the software is that you are trialling? It could be that there's a restriction in there that prevents things from being viewed from anything other than localhost.
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Considering you don't mention which library you're using to generate the chart, no, noone can help you.
And if it says that you have to buy it in order to use it in IIS, I think the solution to your problem is very clear, fork over the cash and buy the library...
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As per this previous thread [click me] (some websmartchart control that I have absolutely no knowledge about).
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Please don't use such a Big subject line.
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This is my third attempt to leave this question. The first time I submitted (without keeping a copy of the text - Grrr!) the submission apparently failed and I was left staring at a white screen. The second time was similar, though I did keep a copy.
I am writing a Class to monitor and manage a WiFi-enabled HVAC thermostat which communicates using UDP packets. It sends out a "status report" containing various data every 10 seconds, which I am able to receive (using an asynchronous thread) and decode with no difficulty. Because the thermostat and its WiFi module are relatively slow and single-threaded, I have set the Class up so that settings changes are processed in its main thread and the resulting commands are sent out synchronously from the receiving thread after the status report is received and processed. This is where I have run into som problems.
It appears that if I do not insert pauses (using Thread.Sleep) before and/or between using .Send to transmit each command packet, some packets do not get transmitted (confirmed by using a packet sniffer on the network). In addition, the first packet of at least some combinations of commands appears not to be sent if I do not include an Application.DoEvents call before the pause that precedes it. Putting in breakpoints and/or stepping through the Class code abolishes all misbehavior! This worries me a) because I don't like behavior I don't understand, and b) because I had planned to make the Class into a Class Library, which appears to preclude the use of Application Methods.
The current version of the code is as shown below. Does anyone have any ideas as to what may be going on?
Private Sub ReceiveMessages()
Try
Dim receiveBytes As [Byte]() = TCudpClient.Receive(RecEndpoint)
' Some error checking code omitted
Process_Heartbeat(receiveBytes)
If NewSettings Then ' There are some queued commands
UpDating = True ' Set a flag to prevent new commands being added while we are processing existing ones
Send_Commands() ' See below
UpDating = False
NewSettings = False
End If
ThreadReceive = New System.Threading.Thread(AddressOf ReceiveMessages)
ThreadReceive.Start()
Catch ex As System.Threading.ThreadAbortException
' this generally means that the thread was deliberately aborted, so we can ignore it
Catch e As Exception
If Not ShuttingDown Then Throw New ApplicationException("Problem receiving data from Thermostat" & vbCrLf, e)
End Try
End Sub
Private Sub Send_Commands()
Static blInitDone As Boolean
If Not blInitDone Then
TCudpClient.Connect(IPAddress.Parse(IPText), COMMANDPORT) ' presumably only need to do this once
'It appears that the first message sent after the Connect command sometimes fails to be transmitted,
'so we make sure that it gets sent twice
For Each tc In ThermostatCommands ' find the first available command
If tc.Pending Then
Application.DoEvents()
System.Threading.Thread.Sleep(100)
SendMessage(tc.ComBuff) ' See below
Exit For
End If
Next
blInitDone = True
Else
End If
For Each tc In ThermostatCommands
If tc.Pending Then
Application.DoEvents()
System.Threading.Thread.Sleep(100)
SendMessage(tc.ComBuff) ' See below
tc.ComBuff = Nothing
tc.Pending = False
End If
Next
End Sub
Private Sub SendMessage(ByVal bytArray() As Byte)
Dim intReturn As Integer
intReturn = TCudpClient.Send(bytArray, bytArray.Length)
If intReturn <> bytArray.Length Then
Throw New ApplicationException("Problem sending command to Thermostat")
End If
End Sub
modified on Thursday, September 9, 2010 4:47 PM
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Hi Peter,
1.
the blank pages are a known problem, the powers that be are working hard to get it fixed.
2.
I think you have some threading problems. Here are two things I don't like at all:
2a.
Sub ReceiveMessages() is creating and launching a thread that executes ReceiveMessages(). So you seem to want the code to run repetitively, however instead of using a loop, you create a new thread all the time?
2b.
Application.DoEvents() is evil; when used, AFAIK it should be called only by the main thread, not by any other thread. And I don't think you need it at all.
3.
It is not obvious to me how you intend on using all the code shown, as it consists of subs only. If you need further help, I suggest you explain it a bit more and indicate how/where/when something gets called (e.g. ReceiveMessages() is called from the main form's constructor; or from a button_clicked handler; ...)
Hope this helps.
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2a I am following a model published elsewhere, though the logic did make sense to me. The .Receive call needs to be in an independent thread - it is first activated from initialisation code. When ReceiveMessages is invoked on its thread, the thread stalls (for up to 10 seconds) until the UDPClient.Receive call returns. It then does the necessary processing and ends after invoking a new copy of itself on a new thread. Only one ReceiveMessages thread is in existence at a time (except for the very short time after the reinvocation and before the invoking thread terminates), or at least, that is what I assumed. I am not sure why you feel that using a loop would be better, though I also don't think it would be worse.
2b You are not the only one who thinks that Application.DoEvents is evil, but it seems to be the only thing that produces consistent behavior in this code. I dont know why this should be so, and I would be delighted to replace it with something cleaner that also worked - that was what I was hoping that someone would come up with.
3) This is a moderately large and complex Class (because the Thermostat has lots of bells and whistles!). I should have made it clear that the initial Threading call to ReceiveMessages was from the Class constructor, but I thought that the code which I included, which is all that runs in the problem thread, showed how I had things set up without being excessively long and confusing.
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1.
I'm inclined to use less code; so I'll try and get rid of some. Simpler is better, assuming it works.
2.
I would replace your current Sub ReceiveMessage() by something along these lines:
Private Sub ReceiveMessages()
Try
ThreadReceive = New System.Threading.Thread(AddressOf ReceiverMethod)
ThreadReceive.Start()
Catch ex As System.Threading.ThreadAbortException
' this generally means that the thread was deliberately aborted, so we can ignore it
Catch e As Exception
If Not ShuttingDown Then Throw New ApplicationException("Problem receiving data from Thermostat" & vbCrLf, e)
End Try
End Sub
Private Sub ReceiverMethod()
While Not ShuttingDown
Try
Dim receiveBytes As [Byte]() = TCudpClient.Receive(RecEndpoint)
' Some error checking code omitted
Process_Heartbeat(receiveBytes)
If NewSettings Then ' There are some queued commands
UpDating = True ' Set a flag to prevent new commands being added while we are processing existing ones
Send_Commands() ' See below
UpDating = False
NewSettings = False
End If
Catch ex As System.Threading.ThreadAbortException
' this generally means that the thread was deliberately aborted, so we can ignore it
Catch e As Exception
If Not ShuttingDown Then Throw New ApplicationException("Problem receiving data from Thermostat" & vbCrLf, e)
End Try
End While
End Sub
This makes sure only one extra thread is used, and every execution of the original code is by that one thread (including the very first, which wasn't true at all in the original code). The original with a new thread every so often is expensive on system resources, and has the risk of two of those threads running at the same time, confusing you and making you add code to fix things that could have been avoided.
Note: some details may need fixing (e.g. what exceptions to catch, and how to deal with them)
[ADDED]
Remark: make sure the while loop is blocking somehow; it should not just sit there spinning like mad, wasting lots of CPU cycles; if there is no way to make it block (i.e. wait on something), insert a time delay using Thread.Sleep
[/ADDED]
3.
Just remove the DoEvent stuff.
4.
If you want to send the same thing twice, no need to have two for loops. This should do:
For Each tc In ThermostatCommands ' find the first available command
If tc.Pending Then
System.Threading.Thread.Sleep(100)
SendMessage(tc.ComBuff) ' See below
System.Threading.Thread.Sleep(100)
SendMessage(tc.ComBuff) ' See below
tc.ComBuff = Nothing
tc.Pending = False
Exit For
End If
Next
5.
Not sure what ThermostatCommands is, and why you need a pending flag and why you clear the ComBuff; I would be inclined to create new command objects and stuff them in a Queue. Then the sender does not need a for loop at all, it just pulls the head of the queue and sends it.
6.
I'm pretty sure debugging such application is mind boggling if you create a lot of threads, then try to single-step and watch in some IDE or debugger. I tackle those apps differently, by adding logging code,
making sure each log line gets a time stamp. This article[^] gives the philosophy and some code snippets (in C#, could be done in VB.NET equally well).
7.
After some refactoring along above lines, I would not be surprised if some of your comments became obsolete, I mean the ones about the first message sometimes failing, and possibly also about having to send things twice.
Good luck.
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Thanks!
The short version is that your suggestions about reorganising the Threading certainly simplified things and may well have been 90% responsible for solving the problem (I'll come back to the 10%, below)
The longer version:
1. Agreed!
2. Done, with very minor modifications. The While loop blocks "automatically" on the UDPClient.Receive call, which doesn't return until the next Status Report packet arrives, 10 seconds later.
3. Done (and in one other place in the Class)
4. It was actually only the first packet sent after the (initial and only) UDPClient.Connect call that seemed to have problems - only that packet was sent twice by my original code (the first For loop has an early exit). Your code sends every packet twice, which was not my intention!
5. Threads (up until recently) weren't my thing. Data structures are! There are (IMHO) good reasons for the way I am doing this.
6. I have resorted to this sort of approach once or twice (more when I was writing real-time data acquisition and control stuff), but haven't found it useful in general programming often enough to put the "hooks" for it in my code on a routine basis.
7. It appears from further experimentation with the modified code that you do need delays between at least some calls to UDPClient Methods, and that I wasn't leaving quite enough time between them in some cases. Sleeping for 200 msec seems to work reliably for my situation - 100 msec is not always enough. I think that it is possible that the Application.DoEvents calls were "working" simply because they were wasting more time, and the poor threading code may also have been only a contributing factor to the problems.
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I'm glad you got on top of it, well mostly anyway.
5.
I've done lots of real-time stuff, even with queues. One very neat trick is this:
- create two queues, lets call them FULL and EMPTY; FULL will represent the functional queue, EMPTY will be the store for messages currently not in use;
- create N messages, put all of them in the EMPTY queue;
- have the producer get a message from the EMPTY queue, fill it, and put it in the FULL queue;
- have the consumer get a message from the FULL queue, execute it, and put it in the EMPTY queue.
The net result is you don't need object creation/destruction once things have been initialized; and you get an automatic dataflow-limited behavior, as either queue will never hold more than N items.
It works just great, provided all messages have the same type (or size).
6.
Same here. In embedded systems, you typically want to observe without halting everything, hence logging fits the bill.
What remains to be done IMO is figuring out why you need your delays. Is it related to the reaction time of your thermostat? (i.e. is it deaf while processing an earlier command or transmitting a result?) Timestamped logging should help out here as well.
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5. In this case, all the messages are not the same size (the message header length is constant, but a message can contain 0, 1, 2, or an arbitrary (2 < n <= 26) number of additional bytes of data). Also, for a number of reasons related to the device and application, I want to be able to identify and (if necessary) modify a pending command, if another command of the same "class" is issued before the first one is executed, which may be up to 10 seconds later.
The thermostat is relatively slow (in computer terms), and can only do one thing at a time, but I don't think that this can be causing the need for the delays. If I don't put them in, some of the UPD packets are never sent. It is as if the outgoing UDP port needs time to "clear" before it will send a new message.
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I need help how i can add differen control in datagirdview in a singel column.
Like
ProperName showvaule
testName show value in combox
testName2 show value in text
testName3 show value in combox
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