Exception handling in Azure mobile app table controller

Question

I am working with Azure mobile app table controllers. get syntax is

    public IQueryable<Employee> GetAllEmployee()
    {
        try
        {
        return Query();
        }
        catch(Exception ex)
        {
            throw;
        }
    }

Now the issue here is, since the return method is IQueryable, i am not able to catch exceptions in the catch block, i understand IQueryable is for different requests from client (in my case android). however i want to log errors in the catch block.currently my debugger never lands in catch block . because azure mobile app sdk handles exception and forms http exceptions and all i can see is 500 exception. i want to log errors in database , how can i achieve this?

Answer 1

As you says the return type is IQueryable, so you couldn't catch the exception in the the GetAllEmployee method.

Here is a work around.

I suggest you could use web api global error handling to handle the exception. More details, you could refer to this article and below codes.

In the Startup.MobileApp.cs:

Add this class:

  public class TraceSourceExceptionLogger : ExceptionLogger
    {
        private readonly TraceSource _traceSource;

        public TraceSourceExceptionLogger(TraceSource traceSource)
        {
            _traceSource = traceSource;
        }

        public override void Log(ExceptionLoggerContext context)
        {
            //in this method get the exception details and add it to the sql databse
            _traceSource.TraceEvent(TraceEventType.Error, 1,
                "Unhandled exception processing {0} for {1}: {2}",
                context.Request.Method,
                context.Request.RequestUri,
                context.Exception);
        }
    }

Change the ConfigureMobileApp method as below:

  public static void ConfigureMobileApp(IAppBuilder app)
        {
            HttpConfiguration config = new HttpConfiguration();

            config.Services.Add(typeof(IExceptionLogger),
    new TraceSourceExceptionLogger(new
    TraceSource("MyTraceSource", SourceLevels.All)));


            new MobileAppConfiguration()
                .UseDefaultConfiguration()
                .ApplyTo(config);

            // Use Entity Framework Code First to create database tables based on your DbContext
            Database.SetInitializer(new MobileServiceInitializer());

            MobileAppSettingsDictionary settings = config.GetMobileAppSettingsProvider().GetMobileAppSettings();

            if (string.IsNullOrEmpty(settings.HostName))
            {
                app.UseAppServiceAuthentication(new AppServiceAuthenticationOptions
                {
                    // This middleware is intended to be used locally for debugging. By default, HostName will
                    // only have a value when running in an App Service application.
                    SigningKey = ConfigurationManager.AppSettings["SigningKey"],
                    ValidAudiences = new[] { ConfigurationManager.AppSettings["ValidAudience"] },
                    ValidIssuers = new[] { ConfigurationManager.AppSettings["ValidIssuer"] },
                    TokenHandler = config.GetAppServiceTokenHandler()
                });
            }

            app.UseWebApi(config);
        }