I am using the azure-mobile-apps-net-server SDK for my smartphone app backend. Now I want to show the smartphone user some message, when there is a new update available. My idea is to include the current version number of the smartphone app in the header of the request, which goes to the backend.
Now I can read the version in the backend, compare it to some value and throw an HttpResponseException, which the client will catch. Then I can show the client user some message to update to a newer version.
Here some pseudocode:
public void ValidateClientVersion()
{
var version = request.header["X-Client-Version"];
if (version != 3.2.1)
throw new HttpResponseException(...);
}
Now my problem I have multiple Actions in multiple TableControllers. I think there must be some very simple way to call ValidateClientVersion()
before any of the Actions is called. I don't want to add the method call in every single Create, Update, Delete, ... Action.
However as I am new to ASP.Net? or what ever the azure-mobile-apps-net-server Framework is called, I don't know this simple solution.
Can someone point me in the right direction?
It's probably a bad idea to do this over every single version. Your better bet from a user experience perspective is to create a simple WebAPI in your mobile backend that returns the current version, potentially with a download link (based on the OS of the connecting mobile app).
When your mobile app connects, it first calls the WebAPI. If the WebAPI has a different version, then pop up the message and the download link and exit.
This is similar to what we suggest for offline sync schema changes. If the schema version changes, wipe the offline sync SQLite and re-sync.
If you really want do do that you can create a subclass of ApiController, lets call it MyController and make your controllers all derive from it.
Then override the ExecuteAsync function in MyController, put your logic there and end the function with return await base.ExecuteAsync(controllerContext, cancellationToken); so it continues to execute the code in your controller.
Related
I have two Asp.Net web apps, App 1 and App 2. They both use the same database. I am trying to give command from App 1 and immediately run a bit of code in App 2.
The only way I can think of doing this is by inserting a command in the database and have App 2 poll the database every few minutes. But this means there may be a delay in running the code.
Is there a way to run code in App 2 immediately?
You can fire an HttpRequest from one app to another and the code will run almost immediately.
I don't know what language and platform you're using, so it's hard to give you concrete examples, but here are the outlines:
Create a page in App2. In standard ASP.Net, you can use a handler. In ASP Core, you can use an API controller. Both car return a single value or a full object in JSON or XML. Or you can use a standard page if you like to return HTML. The code behind is what you want to run. The rendered page or return value from the handler or controller is what you want App1 to get back in response.
Then from App1, issue an HttpRequest to that page in App2 and check the response to see how to continue (for example, if the code ran successfully or not).
The HttpRequest is in case you want to make the call from the server side of App1. If you want to make the call from the client side, then you use Ajax instead. In the case of Ajax, you have to pay attention to the security side, because you don't want to allow whoever to call that page from App2 unless it unless the code behind doesn't pose any security risk and doesn't return any sensitive data.
One last idea specific to your scenario, since both apps are using the same database, you can add the required values to the database as you were planning to do, and then issue a simple HttpRequest. This way, you don't need to worry about security or passing a any sensitive info. When App2 receives the request, it checks the database to see if the request was actually made from App1 and then processes it, otherwise ignores it.
I am working in Asp.Net MVC, i have a scenario as follows.
"Employee will have specific end time to finish a task, once the time is completed, a mail has to be sent automatically to the team lead to notify."
In some way i have to check server datetime and the specified end datetime constantly,my frnd suggested me to check the database datetime with the endtime for every 30 secs by creating a console scheduler to watch the time, do i have any alternative to do this without checking the database frequently?
I would suggest a windows service to check the timings.
do i have any alternative to do this without checking the database
frequently
You could implement some kind of caching mechanism - keep all tasks in memory and check against server time - however if the tasks are updated frequently this cache would quickly become outdated or you need a way to synch the cache with the database.
So I would usethe approach to check every x seconds (30 seconds seems very little, how accurate do you want your notifications to be?? Perhaps once every 5 minutes will be enough depending on your requirements).
If you know the task's end time (that is, the time when the email is supposed to be sent) then I would recommend that you schedule a task to call your ASP.NET MVC application back at the exact moment you need to send the email message. This would allow you to avoid having to 'poll' the server. To do this, I would recommend that you take a look at the Revalee open source project.
Revalee is a service that allows you to schedule web callbacks to your web application. In your case, you would schedule a callback that would send an email message at a specific time. Revalee works very well with tasks that are discrete transactional actions, like sending an automated email message or updating some database values (read: not long running). By using Revalee, the code to perform your action would all reside within your web application.
To use Revalee, you would:
Install the Revalee Service, a Windows Service, on your server. The Windows Service is available in the source code (which you would compile yourself), in a precompiled version available at the Revalee website, or easily installable via Chocolatey.
Use the Revalee client library in your Visual Studio project. (There is an MVC-specific version too.) The client library is available in the source code (which, again, you would compile yourself) or in a precompiled version available via NuGet.
You would register a future callback when you know the end time for the user's task:
private void ScheduleTaskEndEmail(int taskId)
{
// The DetermineTaskEndTime() method is a private method
// (of your creation) which returns a task's end time as
// a DateTimeOffset
DateTimeOffset callbackTime = DetermineTaskEndTime(taskId);
// The callback should at the task's end time
Uri callbackUrl = new Uri(
string.Format(
"http://mywebapp.com/Email/SendTaskEndEmail/{0}",
taskId
)
);
// Register the callback request with the Revalee service
RevaleeRegistrar.ScheduleCallback(callbackTime, callbackUrl);
}
4.When Revalee calls your application back, your app would perform whatever action you have coded it to do. In the Email controller, your SendTaskEndEmail action (see the Uri above) might look like:
[AllowAnonymous]
[CallbackAction]
public ActionResult SendTaskEndEmail(int taskId)
{
// TODO 1. Validate the taskId,
// 2. Lookup the task's information, &
// 3. Send the email message
// ...
return new EmptyResult();
}
The Revalee website has a complete API Reference as well as instructions on how to install and configure the Windows Service. I hope this helps.
Note: The code example above uses a synchronous version of ScheduleCallback(), the Revalee client library also supports asynchronous calls à la:
RevaleeRegistrar.ScheduleCallbackAsync(callbackTime, callbackUrl);
In case it was not clear above, the Revalee Service is not an external 3rd party online scheduler service, but instead a Windows Service that you install and fully control on your own network. It resides and runs on a Windows server of your own choosing where it can receive callback registration requests from your ASP.NET MVC application.
Disclaimer: I was one of the developers involved with the Revalee project. To be clear, however, Revalee is free, open source software (MIT license). The source code is available on GitHub.
So I'm integrating SignalR and HotTowel, although really I think this is a matter of how to integrate with Durandal itself.
The issue is I have obviously multiple views. Some of these views I want to respond to SignalR messages. The question is how to do this integration considering that SignalR events have to be started before I call SignalR's hub start method.
So take the example I have view1 and view2. I want each to do something when a SignalR message is received and in the context of that view (so let's say update the DOM somehow). It's an SPA obviously so calling the SignalR start method for each view seems like a bad idea, so starting SignalR once at boot sounds like the right plan, but at that point my views may not have been loaded, and still how would I ensure that my events have the right context for the page.
This is based on my understanding that all events for SignalR have to be registered before I call start. Any thoughts clever people of StackOverflow?
Edit to expand on the problem
Part of the website involves uploading files for parsing and processing to import into a database. I have created a view where the file is selected and uploaded (using FineUploader) to a WebApiController. The controller does the basic steps of checking the uploaded file and then starts an async task to actually do the parsing and processing, while immediately returning the basic "Yep that uploaded fine" message.
This causes the list of 'in progress' files to refresh and the file appears with an 'Uploaded' status. As the async task occurs, the file is parsed, then processed against a rules system, and then finally imported into another back end data store. As each of these status changes occur, SignalR sends messages to the client to notify them of these changes, and thus update the status against the filename. In order for this to occur I must attach a function to the event as it received in SignalR. That even needs some kind of reference to my view (actually viewmodel) so it can update the correct value.
As SignalR should be started once with a call to hub.Start(), I am trying to do it during the 'boot' phase. However when my SPA starts, that view has not been loaded, and therefore neither has that viewmodel, and therefore my function that is responsible for initialising SignalR can have no understanding of the view/viewmodel it must update.
Examples I've seen on using SignalR show it being used in one view, but that doesn't really work surely if you need it in multiple views (you can't just keep calling hub.start() can you)?
Sorry, if this still doesn't make sense I'll post some code or something.
If you use
$.connection.myHub.on("myMethod", function (/* ... */) { /* ... */ });
instead of
$.connection.myHub.client.myMethod = function (/* ... */) { /* ... */ };
you can add client-side hub methods after calling $.connection.hub.start();
Other than using a web service, is there anyway to call a method in a web app from a windows application? Both run on the same machine.
I basically want to schedule a job to run a windows app which updates some file (for a bayesian spam filter), then I want to notify the web app to reload that file.
I know this can be done in other ways but I'm curious to know whether it's possible anyway.
You can make your windows app connect to the web app and do a GET in a page that responds by reloading your file, I don't think it is strictly necessary to use a web service. This way you can also make it happen from a web browser.
A Web Service is the "right" way if you want them to communicate directly. However, I've found it easier in some situations to coordinate via database records. For example, my web app has bulk email capability. To make it work, the web app just leaves a database record behind specifying the email to be sent. The WinApp scans periodically for these records and, when it finds one with an "unprocessed" status, it takes the appropriate action. This works like a charm for me in a very high volume environment.
You cannot quite do this in the other direction only because web apps don't generally sit around in a timing loop (there are ways around this but they aren't worth the effort). Thus, you'll require some type of initiating action to let the web app know when to reload the file. To do this, you could use the following code to do a GET on a page:
WebRequest wrContent = WebRequest.Create("http://www.yourUrl.com/yourpage.aspx");
Stream objStream = wrContent.GetResponse().GetResponseStream();
// I don't think you'll need the stream Reader but I include it for completeness
StreamReader objStreamReader = new StreamReader(objStream);
You'll then reload the file in the PageLoad method whenever this page is opened.
How is the web application loading the file? If you were using a dependency on the Cache object, then simply updating the file will invalidate the Cache entry, causing your code to reload that entry when it is found to be null (or based on the "invalidated" event).
Otherwise, I don't know how you would notify the application to update the file.
An ASP.NET application only exists as an instance to serve a request. This is why web services are an easy way to handle this - the application has been instantiated to serve the service request. If you could be sure the instance existed and got a handle to it, you could use remoting. But without having a concrete handle to an instance of the application, you can't invoke the method directly.
There's plenty of other ways to communicate. You could use a database or some other kind of list which both applications poll and update periodically. There are plenty of asynchronous MQ solutions out there.
So you'll create a page in your webapp specifically for this purpose. Use a Get request and pass in a url parameter. Then in the page_load event check for this paremter. if it exists then do your processing. By passing in the parameter you'll prevent accidental page loads that will cause the file to be uploaded and processed when you don't want it to be.
From the windows app make the url Get request by using the .Net HttpWebRequest. Example here: http://www.codeproject.com/KB/webservices/HttpWebRequest_Response.aspx
Everyone probably notices that most modern applications nowadays has a way for user to send crash/bug report either automatically or with user permission. Some examples are Mozilla Crash Reporter or most Microsoft applications.
I really like this feature since it allows me to collect the bugs report quickly with helpful information than just let my user reports the bug/issue traditionally such as submit a help ticket.
I wonder if there is an easy or systematic way to implement that capability in ASP.NET web application.
Have you guys had any experience or knowledge to share for both WebForms and MVC applications? Or if this could be implemented in Client-side like JavaScript/JQuery, that'd be good.
Thanks!
ASP.NET 2.0 introducted Health monitoring, which allows you to do this by just adding some stuff to the web.config. See: http://msdn.microsoft.com/en-us/library/ms998306.aspx
It can log to mail, sql, eventlog, etc. and allows you to set buffers. So it for example won't kill your mailserver if the sql database goes down or if some user discovers a bug and tries to call it too often a second :-)
You can also log failed authentication and app pool restarts with it, it's pretty usefull if you just need it working quick. It's still questionnable if it is the best solution to manage all the errors. Because it might not got all the information you need, for example browser version or smt like that.
ELMAH is a library that plugs in and detects exceptions. You can also log an event yourself. The events and a great deal of data like url parameters and browser information can be emailed to administrators and optionally stored in a database for display. (Rather like an event log for the web site.) It doesn't have a built-in user form that I've seen, but can probably be extended to include such an option.
I've been using/customizing it for about two years now and it is really exceptional.
Another option might be to use Kampyle which includes a feedback box on the bottom right of your web site. You could use Javascript to trigger the box to appear if an issue is detected on the web site.
For an ASP.NET applicatino--or any Web application for that matter--isn't this just a two-step process of:
Logging the error (obviously); and
Put a form on the error document to allow the user to enter feedback.
Or is there more to this?
Your errors will pass through the Application_Error method of the Global.asax.cs file (which you may have to create). I use this fact to capture the error and log it to a database:
void Application_Error(object sender, EventArgs e)
{
try
{
SqlConnection errConnection = new SqlConnection("Your connection string");
// After setting up a command object, I call a stored procedure to save information about
// the crash. I pass two primary arguments. The first is the URL:
errCommand.Parameters.Add("#URL", SqlDbType.VarChar).Value = Request.Url.ToString();
// The second is the error information.
errCommand.Parameters.Add("#EI", SqlDbType.Text).Value = Server.GetLastError().ToString();
// I pass some other information from my session as well...
// After setting up an output parameter called ErrorID, I call the command...
errCommand.ExecuteNonQuery();
// Now Error ID is stored in the session.
Session["ErrorID"] = (int)ErrorID.Value;
}
catch { } // I do NOT want the error handling call to throw an error.
}
Now, you should have set up your Web.Config file so that a specific page gains control when an error occurs. In this page, you'll check the session for the error ID and show it to the user. In the output, I ask the user to write down the error if they would like to call us for more information. If we do receive a request, I can go into the database and get a complete trace of the error.
You can checkout my tutorial on how to implement exception logging in asp.net - http://jesal.us/blog/index.php/2008/04/08/exception-logging-using-the-database/