I've been asked to research approaches to deal with an app we're supposed to be building. This app, hypothetically a Windows form written in C#, will issue commands directly to the server if it's connected, but if the app is offline, the state must be maintained as if it was connected and then sync up and issue data changes/commands to the server once it is connected.
I'm not sure where to start looking. This is something akin to Google Gears, but I don't think I have that option if we go a Winform route (which looks likely, given that there are other functions the application needs that a web app couldn't perform). Is the Microsoft Sync framework a viable option? Does Silverlight do anything like this? Any other options? I've Googled around a bit but would like the community input on what's best given the scenario.
The Microsoft Sync Framework definitely supports the scenario you describe, although I would say that it's fairly complicated to get it working.
One thing to understand about the Sync Framework is that it's really two quite distinct frameworks shipping in the same package:
Sync Framework
ADO.NET Sync services v. 2
The ADO.NET Sync services are by far the easiest to set up, but they are constrained to synchronizing two relational data stores (although you can set up a web service as a remote facade between the two).
The core Sync Framework has no such limitations, but is far more complex to implement. When I used it about six months ago, I found that the best source to learn from was the SDK, and particularly the File/Folder sync sample code.
As far as I could tell, there was little to no sharing of code and types between the two 'frameworks', so you will have to pick one or the other.
In either case, there are no constraints on how you host the sync code, so Windows Forms is just one option among many.
If I understand correctly, this doesn't sound like an actual data synchronization issue to me where you want to keep two databases in sync. it sounds more like you want a reliable mechanism for a client to call functions on a server in an environment where the connection is unstable, and if the connection is not present at the time, you want the function called as soon as the connection is back up.
If my understanding is right, this is one option. if not, this will probably not be helpful.
This is a very short answer to an in-depth problem, but we had a similar situation and this is how we handled it.
We have a client application that needs to monitor some data on a PC in a store. When certain events happen, this client application needs to update our server in the corporate offices, preferably Real-Time. However, the connection is not 100% reliable, so we needed a similar mechanism.
We solved this by trying to write to the server via a web service. If there is an error calling the web service, the command is serialized as an XML file in a folder named "waiting to upload".
We have a routine running in our client app on a timer set for every n minutes. When the timer elapses, it checks for XML files in this folder. If found, it attempts to call the web service using the information saved in the file, and so on until it is successful. Upon a successful call, the XML file is deleted.
It sounds hack-ish, but it was simple to code and has worked flawlessly for five years now. It's actually been our most trouble-free application all-around and we've implemented the pattern elsewhere successfully
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I was learning more about ASP.NET MVC, and I decided to to take a course on Udemy taught by Mosh Hamedani, and this course involved me making an application called Vidley. I was able to complete the course entirely, however I came across a problem:
A day or two after I completed the course. My computer caught a virus and I had to reformat the operating system and reinstall everything. I had the application backed up on bit bucket, but the application just doesn't work with the database. When ever I try to create a new user, the application just throws an error. What do I need to do to get the application working with the database again. I tried looking at other topics but I couldn't see anything that covered my specific issue. I am thinking if there is any kind of configuration I need to fix with the database, but I am not entirely sure and I am concerned I will break the code.
It really is upsetting because I was going to add that project to my portfolio, so I could find a job easier. I am wondering what I have to do to get this web application to work with the database again, and where should I deploy it. Should I use a website like app harbor, or is there any other better platform. I am really new at this so I am sorry if I am asking an absurd question.
Please recheck your connection string as you have reinstalled everything even the operating system.
Check your Database server instance is running or not. If not, start that service.
Recheck database name, username and password in your connection string.
I'm about to release a small tool which uses a database connection for storing data. The question is: How can I prevent people reverse engineering my code and getting the Username and Password to gain access to the database?
For earlier projects (which were used only by myself), I defined the connection-string just as a global variable inside my app. But that's highly unsafe as it only takes minutes to get this string out of the exe.
Also a lot of methods to obfuscate code can be reversed.
I am really a big fan of providing code but I don't know what to post. This is more a question about the theory. Coding is the part I'll take care of myself.
Here is a small idea from me which I don't really like that much:
I could place a second tool on the server. The real app would connect to this second tool, give over the data and the second data would finally connect to my database itself. This way the connection-string would be stored inside the second app where nobody can grab it.
The fact of the matter is that storing sensitive information on the client machine is highly vulnerable to attacks against your database. A suggestion you can look into is a Three-tier architecture model for your application (http://en.wikipedia.org/wiki/Multitier_architecture#Three-tier_architecture). In a Three-tier architecture, you have your presentation layer (your application), your logic tier (this layer will be the central pit stop for all your clients will have access to your database), and you have your database layer (the server where your database is). With this architecture, you can ensure all the data being stored and being retrieved from is from a singular source and high level security.
In the past (and still in the present), programmers would have to create their own socket servers or do advance network programming to develop a solution like this, however Microsoft has developed a tool called Windows Communication Foundation (WCF) which takes away the pain of coding your own socket server and lets you focus on developing your own implementation. Be warned though, WCF is secure by default, but it is no excuse not to research into ways of making your product robust against hackers (like knowing what protocol you are going to use, what security measures you are going to use (Transport vs Message, etc), encrypting data on client side so potential viruses don't uncover sensitive informations, etc). In saying that, WCF is a highly polished service and is really easy to get something up and running.
A good beginner video tutorial on WCF can be found here: https://www.youtube.com/playlist?list=PLhq7kqloVlM-bI9W_7iDZhObAeyrFt1y_
EDIT: The playlist for the videos are gone, but the videos themselves are still there. Just search through all his videos looking for the keyword 'WCF'
Here's the link: https://www.youtube.com/user/JesseDietrichson/featured
This is my first time dabbling in windows services.
I have a service I would like to manage, I would like to be able to connect to this service via a command line / REPL of sorts to avoid the development time of working on a user interface. I was thinking we could communicate much like attaching to an Asterisk daemon or somewhat like connecting to a MySQL server which to me seems like nothing more than a simple custom shell spawned to handle requests. However, I am always concerned about how efficient my code is and would like to keep to common practices. This will be connecting on the same local machine.
My proposed solution:
I believe I can make simple network stream, to create a simple Read - Eval - Print - Loop.
Another option is to use WCF, however my question would then be, how efficient is this as opposed to packet handling?
My question:
What are some standard practices for communicating with or managing services on the local machine?
I'm trying to learn more about service-oriented design, any resources that could help explain common practice models would be much appreciated.
Of course there are so many ways to do this. The way I would recommend is to make sure you use log4net (or some other logging framework) and log the important info. Create the solution with 3 projects, the first will be the "service logic" or the business service, with the second being the windows service wrapper that starts that service, and the third being a console app that does much the same as the windows service only giving you the ability to interact as you wish. The advantage of the console logging appender is that you still get the console output without actually writing to the console... it give good separation.
I will give another option that I have used in the past, but would give with caution. You can selfhost a WCF service inside a windows service. It gives a nice interface that gets away form the messy self rolled TCP server approach. The caution is that if done wrong it can eat up lots of memory and CPU cycles.
my distributed program need update couple of files, i would like it to work the way like those anti virus software updating there virus definition database, is there such framework?
Edit:
I am not updating the application itself.
when the update is done, the application may need reboot.
A server will be open for update query and downloading.
It really depends on the how your data is formatted. If you're keeping a simple local storage in text files, then it's just a matter of hitting up a server and checking if there is a new version of the file(s). If you're keeping things in local SQL storage, then you could use web services to ensure the local storage has the most up-to-date entries. I think that option is what you're looking for, and it would be really easy to write. However, if you're looking to update applications, then something like ClickOnce might be ideal.
In response to your edits
Basically, you have to structure your application to read all information from information files and give those files some meta-information like a "version number" or something like that. Then, you have an ASP.NET web service which has two functions: one is to get the latest version of the information files and the second is to download the updates needed to patch from one version to the current. So, the application would intermittently check with the server to see if there is a newer version than what they have. If there is a newer one, then it would ask the server for the patch files needed to get to the latest version. If you do this before the application actually starts (a la Firefox), the user doesn't even have to notice that the application is restarting.
As far as I know, I am not aware of such a framework. However, the magical stuff is done by Web services or Windows Services looking for updates at a HTTP or FTP location. You might perhaps wirte yourself a code that would launch the script you deploy with your update.
Perhaps this would help a bit: Loading Assemblies. In short, this is the way plugins are plugged in your application, using proxies and so forth.
As mentioned by #Travis G, ClickOnce is good for application. Just different approach! =)
So my company stores alot of data in a foxpro database and trying to get around the performance hit of touching it directly I was thinking of messaging anything that can be done asynchronously for a snappier user experience. I started looking at ActiveMQ but don't know how well C# will hook with it. Wanting to hear what all of you guys think.
edit : It is going to be a web application. Anything touching this foxpro is kinda slow (probably because the person who set it up 10 years ago messed it all to hell, some of the table files are incredibly large). We replicate the foxpro to sql nightly and most of our data reads are ok being a day old so we are focusing on the writes. plus the write affects a critical part of the user experience (purchasing), we store it in sql and then just message to have it put into foxpro when it can. I wish we could just get rid of the foxpro, unfortunately the company doesn't want to get rid of a very old piece of software they bought that depends on it.
ActiveMQ works well with C# using the Spring.NET integrations and NMS. A post with some links to get you started in that direction is here. Also consider using MSMQ (The System.Messaging namespace) or a .NET based asynchronous messaging solution, with some options here.
MSMQ (Microsoft Message Queueing) may be a great choice. It is part of the OS and present as an optional component (can be installed via Add/Remove Programs / Windows Components), meaning it's free (as long you already paid for Windows, of course). MSMQ provides Win32/COM and System.Messaging APIs. More modern Windows Communication Foundation (aka Indigo) queued channels also use MSMQ.
Note that MSMQ is not supported on Home SKUs of Windows (XP Home and Vista Home)
Its worth mentioning that the ActiveMQ open source project defines a C# API for messaging called NMS which allows you to develop against a single C# / .Net API that can then use various messaging back ends such as
ActiveMQ
MSMQ
TibCo's EMS
any STOMP provider
any JMS provider via StompConnect
You may want to look at MSMQ. It can be used by .NET and VFP, but you'll need to rewrite to use them. Here's an article that tells you how to use MSMQ from VFP. https://learn.microsoft.com/en-us/previous-versions/visualstudio/foxpro/ms917361(v=msdn.10)
Sorry if this isn't what you are asking for...
Have you considered some sort of cache behind the scenes that acts a bit like the "bucket system" when using asynchronous sockets in c/c++ using winsock? Basicly, it works by accepting requests, and sends an immediate response back to the web app, and when it finally gets around to finding your record, it updates it on the app via AJAX or any other technology of your choice. Since I'm not a C# programmer I can't provide any specific example. Hope this helps!
Does the Fox app use .CDX indexes? If so, you might be able to improve performance by adding indexes without needing to change any program code. If it uses .IDX indexes, though, the change would have to be done in the actual app.
As the problem is with writes, I would look more towards >removing< any unneeded indexes on the tables. As is common in RDBMS, every index on a FoxPro table slows down a write operation as the indexes need to be updated, and as you aren't reading directly from (or presumably directly querying) the table you shouldn't need very many indexes. You might also want to look at any triggers or field rules on the tables as they may be slowing down the write operation. Be sure your referential integrity is still preserved, though..