While performing some local testing on an Azure Mobile Services (C# backend) app, I kept getting a 400 Bad Request whenever I tried to perform an update to an Entity:

await MobileService.GetTable<MyEntity>().UpdateAsync(myEntity);

I ensured that my entity object was populated correctly and that I was providing an Id as part of the request but was still getting the following error:

“Microsoft.WindowsAzure.MobileServices.MobileServiceInvalidOperationException: The request could not be completed.  (Bad Request)\r\n   at Microsoft.WindowsAzure.MobileServices.MobileServiceHttpClient.<ThrowInvalidResponse>d__18.MoveNext()\r\n— End of stack trace from previous location where exception was thrown —\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()\r\n   at Microsoft.WindowsAzure.MobileServices.MobileServiceHttpClient.<SendRequestAsync>d__1d.MoveNext()\r\n— End of stack trace from previous location where exception was thrown —\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   at Micr
osoft.WindowsAzure.MobileServices.MobileServiceHttpClient.<RequestAsync>d__4.MoveNext()\r\n— End of stack trace from previous location where exception was thrown —\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   at Microsoft.WindowsAzure.MobileServices.MobileServiceTable.<>c__DisplayClass21.<<UpdateAsync>b__20>d__23.MoveNext()\r\n— End of stack trace from previous location where exception was thrown —\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   at Microsoft.WindowsAzure.MobileServices.MobileServiceTable.<TransformHttpException>d__51.MoveNext()\r\n— End of stack trace from previous

Not the most descriptive error hence my decision to create the post.  The end result is that within my C# backend project I declared an entity within my DataObjects class.

public class MyEntity:EntityData
   {
       public string Id { get; set; }

As soon as I removed the Id from this class my updates were successful.

In the end it was a silly error on my part as within my Mobile App Model classes you need to declare this Id as part of your class. This is not the same case with your backend classes.  I have several other Entities in this project and knew that you should not declare this Id but it slipped through the cracks.

It is also worth noting that during this time I could successfully insert records even though this Id was declared.