Db context on azure app service (mobile) fails

Question

I have a controller running on Azure App Service - Mobile. The trace shows that the below code runs fine until db.SaveChanges() this fails.

var telemetry = new Microsoft.ApplicationInsights.TelemetryClient();
telemetry.TrackTrace("Create User");
using (BCMobileAppContext db = new BCMobileAppContext())
{
     string Username_NoSpaces = username.Username.Replace(" ", "");
     var user = db.Users.FirstOrDefault(u => u.Username_NoSpaces == Username_NoSpaces || u.MicrosoftToken == this.User.Identity.Name);
     telemetry.TrackTrace("1");
     if (user == null && !Username_NoSpaces.Contains(","))
     {
          telemetry.TrackTrace("2");
           DateTime now = DateTime.UtcNow;
           telemetry.TrackTrace("3");
           string username_noSpaces = username.Username.Replace(" ", "");
           DataObjects.User userItem = new DataObjects.User() { Created = now, UserId = this.User.Identity.Name, MicrosoftToken = this.User.Identity.Name, Username_NoSpaces = username_noSpaces, Update = now, Username = username.Username, Gold = 1, Level = 1, Title = "Sir", InGameCrest = "", ReceiveNotifications = true };
           telemetry.TrackTrace("4");
           UserDTO returnObject1 = new UserDTO() { Created = userItem.Created, isCreated = true, MicrosoftId = userItem.MicrosoftToken, Username = userItem.Username };
            telemetry.TrackTrace("5");
            db.Users.Add(userItem);
            telemetry.TrackTrace("6");
            db.SaveChanges();         //Trace and code fails
            telemetry.TrackTrace("7");
            UserDTO returnObject = new UserDTO() { Created = userItem.Created, isCreated = true, MicrosoftId = userItem.MicrosoftToken, Username = userItem.Username };
            telemetry.TrackTrace("8");
            return Ok(returnObject);
       }
}

The stacktrace from the diagnostic on the appservice (which I unfortunately do not understand) gives:

2016-04-07T17:29:19  PID[5008] Error       Operation=ReflectedHttpActionDescriptor.ExecuteAsync, Exception=System.Data.Entity.Validation.DbEntityValidationException: Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at BCMobileAppService.Controllers.Test2Controller.Post(UserDTO username) in C:\Users\johann\Desktop\BCMobileApp_Runtime\BCMobileAppService\Controllers\TestController.cs:line 78
   at lambda_method(Closure , Object , Object[] )
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary 2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18 1.MoveNext()
2016-04-07T17:29:19  PID[5008] Error       Operation=ApiControllerActionInvoker.InvokeActionAsync, Exception=System.Data.Entity.Validation.DbEntityValidationException: Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at BCMobileAppService.Controllers.Test2Controller.Post(UserDTO username) in C:\Users\johann\Desktop\BCMobileApp_Runtime\BCMobileAppService\Controllers\TestController.cs:line 78
   at lambda_method(Closure , Object , Object[] )
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary 2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18 1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18 1.MoveNext()
2016-04-07T17:29:19  PID[5008] Error       Operation=Test2Controller.ExecuteAsync, Exception=System.Data.Entity.Validation.DbEntityValidationException: Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at BCMobileAppService.Controllers.Test2Controller.Post(UserDTO username) in C:\Users\johann\Desktop\BCMobileApp_Runtime\BCMobileAppService\Controllers\TestController.cs:line 78
   at lambda_method(Closure , Object , Object[] )
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.< >c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary 2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18 1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18 1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.Tracers.HttpControllerTracer.<ExecuteAsyncCore>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18 1.MoveNext()

Update

So I will be trying this, which will give more detailed error message:

catch (DbEntityValidationException dbEx)
{
foreach (var validationErrors in dbEx.EntityValidationErrors)
{
    foreach (var validationError in validationErrors.ValidationErrors)
    {
        Trace.TraceInformation("Property: {0} Error: {1}", 
                                validationError.PropertyName, 
                                validationError.ErrorMessage);
    }
}
}

Also

I will go through all the the settings to ensure that the a field that must not be null is null as according to this answer on stackoverflow.

Testing the above

The exception hides that the Id Field is required, is the exception.

The database I have uses EntityData(described here on msdn) where the Id comes from. My use on MobileService was that the Id was created when I executed the line, which fails db.SaveChanges(). Can somebody clarify this? The class looks like this:

 public abstract class EntityData : ITableData
{
    protected EntityData();

    [Index(IsClustered = true)]
    [TableColumn(TableColumnType.CreatedAt)]
    public DateTimeOffset? CreatedAt { get; set; }
    [TableColumn(TableColumnType.Deleted)]
    public bool Deleted { get; set; }
    [TableColumn(TableColumnType.Id)]
    public string Id { get; set; }
    [TableColumn(TableColumnType.UpdatedAt)]
    public DateTimeOffset? UpdatedAt { get; set; }
    [TableColumn(TableColumnType.Version)]
    public byte[] Version { get; set; }
}

Answer 1

There is no auto generate support for string primary key in EF. That's why you should assign your primary key by manually.

You can initilaize Id,CreatedDate and UpdatedDate with constructor.

    public abstract class EntityData : ITableData
    {
     //Change the constructor to initilaize required filled with meaningful data.
        protected EntityData()
        {
          Id=Guid.NewGuid().ToString();
          CreatedDate=DateTime.UtcNow;
          UpdatedDate=DateTime.UtcNow;
        }

        [Index(IsClustered = true)]
        [TableColumn(TableColumnType.CreatedAt)]
        public DateTimeOffset? CreatedAt { get; set; }
        [TableColumn(TableColumnType.Deleted)]
        public bool Deleted { get; set; }
        [TableColumn(TableColumnType.Id)]
        public string Id { get; set; }
        [TableColumn(TableColumnType.UpdatedAt)]
        public DateTimeOffset? UpdatedAt { get; set; }
        [TableColumn(TableColumnType.Version)]
        public byte[] Version { get; set; }
    }

You can override savechanges method in your context. When you modified an entity ,this method will change updateddate automatically.

 public override int SaveChanges()
    {
        //Get Modified Entities
        var modifiedEntries = ChangeTracker.Entries()
             .Where(x => x.Entity is ITableData
                 && (x.State == EntityState.EntityState.Modified));
        foreach (var entry in modifiedEntries)
         {
           var entity = entry.Entity as ITableData;
           //Modify updateddate
           if (entity != null)
            {
              entity.UpdatedDate = DateTime.UtcNow;
            }
         }
        return base.SaveChanges();
    }

Edit: The first solution was general solution which is not realeted with any library.

EntityData you need for serilazation. When mobile client and backend server tries to communicate with each other, this class will help you. For Example mobile client doesn't support navigation properties but backend server does. When you serilaize entitydata, it will hide these properties for you.

If you design your database for this app. Follow this document.

First: You should use EntityData Class which is inside of library. Your models should inherit from it not your EntityData Class.

Second: Your context should have this code on override model creating. You need this for automatic update of created/updated at and Id (This is the answer for your question).

   protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            string schema = ServiceSettingsDictionary.GetSchemaName();
            if (!string.IsNullOrEmpty(schema))
            {
                modelBuilder.HasDefaultSchema(schema);
            }

            modelBuilder.Conventions.Add(
                new AttributeToColumnAnnotationConvention<TableColumnAttribute, string>(
                    "ServiceTableColumn", (property, attributes) => attributes.Single().ColumnType.ToString()));
        }

If you use a database which is already existing follow this document.