How can I catch exception from backend server using IMobileServiceSyncTable - InsertAsync? - azure

Question

I'm using IMobileServiceSyncTable from Azure Mobile App. In InsertAsync operation, on the backend server side, I had some validations for the data and, if that validations failure, I want throw Exception from the server side. I tried return InternalServerError(), throw HttpResponseException, but never worked on the client side. I debbuged the Post method in server side, the server throws the exception or return InternalServerError, but in the mobile client, don't occurs error.
Can anyone help me?
Here is my code on the client side:
public async Task<bool> AddPaciente(Paciente novoPaciente)
{
//other things
try
{
await _pacienteTable.InsertAsync(novoPaciente);
}
catch (Exception e)
{
Debug.WriteLine(e.Message);
Debug.WriteLine(e.StackTrace);
throw new WebException(AppResources.MensagemFalhaConexaoServidorAzure);
}
await SyncPaciente();
return true;
}
Here is my post method on the backend server side
// POST tables/Paciente
public async Task<IHttpActionResult> PostPaciente(Paciente novoPaciente)
{
//other things
if (paciente != null)
{
var responseMessage = new HttpResponseMessage(HttpStatusCode.BadRequest)
{
Content = new StringContent("Já existe um paciente com esse token cadastrado.")
};
//throw new HttpResponseException(responseMessage);
return InternalServerError(new Exception("Já existe um paciente com esse token cadastrado."));
}
}

Answer 1

You should listen to the response status code.
var response = await _pacienteTable.InsertAsync(novoPaciente);
if (response.IsSuccessStatusCode) {
var content = await response.Content.ReadAsStringAsync ();
}
else
{
//Here handle the error code
throw new WebException(AppResources.MensagemFalhaConexaoServidorAzure);
}

Answer 2

I'm using IMobileServiceSyncTable from Azure Mobile App. In InsertAsync operation, on the backend server side, I had some validations for the data and, if that validations failure, I want throw Exception from the server side.
For IMobileServiceSyncTable, you are dealing with An Offline Client which means that IMobileServiceSyncTable<T>.InsertAsync would directly insert data into the local SQLite store on your mobile client-side. Until you manually call MobileServiceClient.SyncContext.PushAsync(), then your local data store would be pushed to your mobile backend. For this approach, I would recommend you make sure that you need to validate the inputs before you saving them into the local data store, otherwise your push operations would fail, then you need to force your client user to adjust the existing inputs even after it has been successfully added before.
If you use An Online Client as follows, then both your approaches for throwing the exception would be immediately returned to your client.
var mobileClient= new MobileServiceClient("https://{your-mobile-app-name}.azurewebsites.net");
var _pacienteTable= mobileClient.GetTable<Paciente>();
await _pacienteTable.InsertAsync(novoPaciente);
Moreover, I used the following code line for catching the exception:
try
{
await table.InsertAsync(item);
}
catch (MobileServiceInvalidOperationException ex)
{
//TODO:
//await ex.Response.Content.ReadAsStringAsync(); //get detailed response content
}
catch (Exception e)
{
//TODO: other uncaught exception
}
Also, for the similar issue, you could leverage Fiddler to capture the network traces to narrow down this issue, make sure your client-side could correctly receive the relevant response.