Suppose I have either an ASP.NET displaying my results, or a Silverlight client. And I'd like to show the current status of my server, or embedded device. (pretend the device reads temperature and humidity stats)
How should I send the status information from my device to the front end? Should I poll the device and save the results to SQL, Azure Table, or the like? (Azure is a technology that fits with this project for other reasons. That's why I mention it)
Or should I create a WCF service that polls the device directly and returns the current status.
What makes more sense?
In either ASP.NET or Silverlight you are going to have to poll from the client (web page or Silverlight app) to the backend to get the current status. In ASP.NET I'd look into doing this via an AJAX poll to a service using Javascipt (look at using Jquery or something similar to make this easier).
In silverlight you will need to have some sort of service configured to return the results and poll it using the Timer control running on a seperate thread.
You can also using a "push" binding within your silverlight app. Basically instead of you manually polling the server, the server will send you a push notification anytime it deems it necessary to let the client know of any change.
Related
I have made a WPF Desktop application that fetches data from an API (on every launch) provided by the website over the Internet and updates its UI accordingly. Now I want to change that. I want to put the application's fetching functionality on the cloud which regularly gets data from API and store it in a SQL SERVER (or any) database. Now I want the application on the client side to get data from the database and not from the API itself (can be on every launch or when there is a change in data).
WHATS THE PROBLEM THEN ?
When thinking of a desktop application over the cloud on a windows virtual machine it feels ok and I understand how to implement it.
But when thinking of a web application the server is supposed to respond to client request and then perform some piece of code to give output/Response. Which I don't need I wan't the code to just run weekly or monthly without client asking.
WHAT I WANT ?
I wan't the server to up 24/7 and updating the database every week.
How usually such kind of thing is implemented in general. Let say for example stack overflow. Don't they perform certain task independent of the client on their servers.
i have a bit theoretical question.
When creating web applications, there is difference to desktop applications with working and active connection to database. So im curious if there is some solution, which can provide more desktop-like access to database e.g. transactions on asynchronous requests from client (web browser)?
edit:
So i figured out, that there can be a transaction process of asynchronous request, from client. Is there solution, which can provide it in web apps?
e.g I have assynchronou ajax call, which consist of multiple operations, and i wana to process them as transaction. If everything is okay, operations will be all done. But if one of them fail, just rollback it. Like its in DB. Is it possible?
edit2: maybe im wrong and the issue is not about ajax, but about whole web applications, but i dont think there is a way how to make a asynchronnous request from web client.
Transaction need continuous connection to database. To make it work with web application you need a platform which allow the application to run continuously independent of client request. Java servlet is best fit, php is a no-no. So I asume you will use java servlet.
In java servlet, you can create a db transaction, create an id for it, and then store them in a static variable or in the provided application-wide object, context. Then, return the id to the client.
When the client want to send another request, make it send the id. The application then can locate the transaction variable based on the id. As long as the application doesn't restarted between the two requests, the transaction is still there and active.
Because web application don't know when the user leave the application, you must create a mechanism to check the transactions periodically, and then rollback it if the user leave them for a specified time period.
The database has no knowledge of who is connected outside of authentication.
All,
I have completed the basic GAE "Guestbook" example which uses Google Cloud Endpoints and Google Cloud Messaging. I can successfully add a note to the guestbook and have it appear on all registered devices.
I've also used the super simple Server Sent Event (SSE) mechanism to have a web page initiate an event source and then update itself as events are received. But separate web pages appear to create their own distinct event sources (even if using the same URI to the event source) and thus get their own events at their own times.
The objective here is to create a bit of collaboration such that user actions can come from an android device or a web page and the effects the received action are then pushed to all connected users/devices/web pages.
I have assumed I will need a background module and that both Endpoints and 'normal' web pages / queries would channel the received user action to that background module. I believe I can get that far. Next, I need the background module to trigger a push notification to all interested parties.
I believe I can trigger a Google Could Messaging event to registered Android devices from that background module.
But it isn't clear to me how a background module can be the source of an SSE, or how the background module can best communicate with a foreground module that already is the source of an SSE.
I've looked at the Google Queue API, but I have a feeling I'm making something quite easy much more difficult than it needs to be. If you were not going to 'poll' for changes from a web page... and you wanted to receive notifications from an SSE source when changes were made by other users, possibly using Android devices rather than a typical web page, and the deployed application is running on the Google Application Engine, what would you recommend?
Many thanks,
Randy
You are on the right track, not really sure why you are using the background module but from what i understood you need to:
Your front end module receives an update
You retrieve a list of all devices receiving that update
Use the Queue service to send the update via GCM to every single device
Why use queues? because front end instances have a 1 min time limit per request and you'll need to queue work in order to go beyond that time to serve you (potentially) thousands of users.
Now, If you already have a backend instance (which does not have the 1min limit) you could just iterate over the list and send all messages on one request. I believe you have a 24 hr request limit so you should be OK. But in this scenario you don't have need for the front end module, you can just hit this server straight up.
I'm working on a client and server application, in which client requests 'client-specific' data from the server. I'm planning on switching to ASP.NET WebAPI for server so that client can take advantage of available .NET APIs to query server for data.
This scenario works perfectly fine when the client initially connects and requests data from server, However, instead of client constantly polling for data, it should just establish a persistent connection and the server should be able to monitor the database for changes and push new data to the client that has stale data. I came across SignalR and found that it can be used with WebAPI, but can't figure out how to integrate it with database monitoring i.e. a thread or process that is constantly monitoring database for updates. Any solution? I'm open to other non-WebAPI based .NET technologies as well - basically anything .NET based that will cut-down on the development time.
ASP.NET Web API supports PushStreamContent. Take a look at the section "Push Content" in http://blogs.msdn.com/b/henrikn/archive/2012/04/23/using-cookies-with-asp-net-web-api.aspx. Here, a timer triggers content written into the stream but you can use that to poll database and write into response or build some other better mechanism
signalR could fit your requirement. You can broadcast a message to all your user or just to part of them. Your client could be a browser (with javascript) or a .net client (WPF or else).
From the server, you can call a method on the client just like that
Clients.All.MyMethodOnTheClient(param1, param2)
or
Clients.Client(connectionId).MyMethodOnTheClient(param1, param2)
The topic is too broad to answer it in 5 min. I can advise you to start here.
Then browse the server api guide, the javascript guide and the .net client guide.
Don't worry. It's quite fast to have a complete tour.
I have two different web applications that need to communicate with each others (which I can currently accomplish by using Silverlight Duplex but that doesn't scale very well). After reading about SignalR, I'd like to give this a try but failed to find much documentation on how to do this. Any advice on ho to get started would be greatly appreciated.
Thanks!
More specific Info:
Example:
Application A (Bidding Interface) - A web page to allow multiple end-users to place bids on certain items.
Application B (Managing Interface) - A web page to allow a user (or could potentially be multiple users) to monitor/control the actions from Bidding Interface.
So when a user from Application A place a bid on a piece, I'll need a way to alert Application B that a bid has been placed. Then from Application B, should the user choose to accept the bid, I need to send an alert back to Application A (to update current price, increase bid etc...)
In all honesty, in might just be simpler to have each application push the notifications to each other via standard service calls (WCF, ASMX, HTTP handler endpoints, MVC controllers, whatever). SignalR is useful in browser to server communications because there isn't a consistent way to do push from the server to a connected browser. But from web app to web app pushing is simple; Application A just calls a service endpoint on Application B to notify it of something happening.
Assuming that what you want is something like ...
User (browser) --- Application A --- Application B --- User (Browser)
Realtime communication can be done by doing the following ...
This isn't the job of signalR however something like NServiceBus would fit this very well.
you reference a bus dll file and hubs can both raise and respond to events.
In your case you would have both SignalR and your Service Bus technology work together to allow the cross application sync.
So the process is something like ...
User in application A fires up browser and requests page.
Application A creates Hub instance which internally subscribes to Service Bus events
User in application B fires up browser and requests page.
Application B creates Hub instance which internally subscribes to Service Bus events
User on either application does some action resulting in SignalR picking up a message.
SignalR raises bus event to say "This user did something" on the service bus.
Other Hub on other Application through subscribription to the event gets notified of the event and takes any action to inform its connected users of it.
Lesson to be learnt here ...
Don't try and make a technology do something beyond its purpose ... use the right tool for the job.
This entire solution can be done with little more than about 20 lines of code after getting the core framework setup.
NServiceBus can be found here:
http://particular.net/nservicebus
Disclaimer: There may be other solutions but this one suggestion don't assume this is the only way this can be solved, and the only technologies that be used in this manner.
I am not affiliated in any way with Particular or the NServiceBus product.