I am attempting to write a Validation attribute in MVC4.
The purpose is to check for the existence of an application reference (just a string that represents a key I wish to prevent a duplicate for).
My data is accessed via WebAPI and because I am using 4.5 I wish to make this asynchronous if possible.
I am perhaps not making the best or appropriate usage of async and await but I would like to know how to call my async method from the overridden IsValid method of the inherited Validation class.
public class UniqueApplicationReferenceAttribute : ValidationAttribute
{
public UniqueApplicationReferenceAttribute() : base(() => "The {0} already exists") { }
public int? ApplicationCount { get; set; }
public override bool IsValid(object value)
{
var myTask = GetApplicationRefCountAsync();
myTask.Wait();
this.ApplicationCount = this.ApplicationCount ?? 0;
if (ApplicationCount > 0)
{
return true;
}
else
{
return false;
}
}
public async Task GetApplicationRefCountAsync()
{
HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:11111/");
client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
var apps = client.GetStringAsync("api/dataapplications");
await Task.WhenAll(apps);
var appList = apps.Result;
this.ApplicationCount = appList.Count();// apps.Count();
}
}
Many thanks,
Dan.
I recommend that you call your WebAPI methods synchronously. ValidationAttribute does not support asynchronous implementations natively, so any synchronous-over-asynchronous code you'll write is just going to be a hack and not actually provide any benefit as compared to the synchronous version.
I'm not able to test this in full, but you should be able to do something like this:
public bool IsValid(object value)
{
var appCount = GetApplicationRefCountAsync().Result;
return appCount > 0;
}
public async Task<int> GetApplicationRefCountAsync()
{
var client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:11111/");
client.DefaultRequestHeaders.Accept.Add(
new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
return await client.GetStringAsync("api/dataapplications")
.ContinueWith(r => Convert.ToInt32(r))
.ConfigureAwait(false);
}
Be careful about using async/await methods in an ASP.NET thread. It's easy to create deadlocks.
Related
In the Azure app service mobile backend service, REST API requests are handled by TableController implementation. These methods can be invoked by using corresponding methods available in client SDKs. So, i can query for a particular entity and update its status from the client side.
But how to invoke them in the server side or within the same controller? For example, if I want to query for a particular todoItem and update its status from some custom method here like
Use LookUp(id) to get the item
Update the status
Use UpdateAsync(id, item)
Here I don't know how to create a Delta object of TodoItem to call UpdateAsync(id, patch) method.
public class TodoItemController : TableController<TodoItem>
{
protected override void Initialize(HttpControllerContext controllerContext)
{
base.Initialize(controllerContext);
initrackerserviceContext context = new initrackerserviceContext();
DomainManager = new EntityDomainManager<TodoItem>(context, Request);
}
// GET tables/TodoItem
public IQueryable<TodoItem> GetAllTodoItems()
{
return Query();
}
// GET tables/TodoItem/48D68C86-6EA6-4C25-AA33-223FC9A27959
public SingleResult<TodoItem> GetTodoItem(string id)
{
return Lookup(id);
}
// PATCH tables/TodoItem/48D68C86-6EA6-4C25-AA33-223FC9A27959
public Task<TodoItem> PatchTodoItem(string id, Delta<TodoItem> patch)
{
return UpdateAsync(id, patch);
}
// POST tables/TodoItem
public async Task<IHttpActionResult> PostTodoItem(TodoItem item)
{
TodoItem current = await InsertAsync(item);
return CreatedAtRoute("Tables", new { id = current.Id }, current);
}
// DELETE tables/TodoItem/48D68C86-6EA6-4C25-AA33-223FC9A27959
public Task DeleteTodoItem(string id)
{
return DeleteAsync(id);
}
}
Just use the standard Entity Framework mechanisms. For instance, to find and update a record with a status, you can just use the context:
var item = await context.TodoItems.Where(i => i.Id.Equals(myId)).FirstOrDefaultAsync<TodoItem>();
if (item != null) {
item.Complete = true;
context.Entry(item).State = EntityState.Modified;
await context.SaveChangesAsync();
}
My EF coding is not the greatest ad-hoc, but you should get the idea. Just do the Entity Framework thing.
It's better to use TableController.ReplaceAsync() method that is already implemented for us here in the source code of EntityDomainManager.
var item = Lookup(item.Id).Queryable.FirstOrDefault();
if (item != null)
{
item.Complete = true;
item = await ReplaceAsync(item.Id, item);
}
The ReplaceAsync() method correctly handles the exceptions, so I would not recommend working directly with the EF context.
In my old non-OWIN APIs, I use a MessageHanlder to log all HttpRequests and HttpResponses. Here is the MessageHandler:
public class MessageHandler : DelegatingHandler
{
private static readonly ILog RequestApiLogger = LogManager.GetLogger("RequestApiPacketLogger");
private static readonly ILog ResponseApiLogger = LogManager.GetLogger("ResponseApiPacketLogger");
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
var correlationId = Guid.NewGuid();
RequestApiLogger.LogHttpRequest(request, correlationId);
return await base.SendAsync(request, cancellationToken).ContinueWith(
task =>
{
var response = task.Result;
response.Headers.Add("http-tracking-id", correlationId.ToString("D"));
ResponseApiLogger.LogHttpResponse(response, correlationId);
return response;
}, cancellationToken);
}
}
However, in my newer projects I could write custom OWIN middleware to do something similar using the OwinContext like this:
//use an alias for the OWIN AppFunc
using AppFunc = Func<IDictionary<string, object>, Task>;
public class LoggingMiddleware
{
private readonly AppFunc _next;
public LoggingMiddleware(AppFunc next)
{
_next = next;
}
public async Task Invoke(IDictionary<string, object> environment)
{
IOwinContext context = new OwinContext(environment);
// Get the identity
var identity = (context.Request.User != null && context.Request.User.Identity.IsAuthenticated)
? context.Request.User.Identity.Name
: "(anonymous)";
// Buffer the request (body is a string, we can use this to log the request later
var requestBody = new StreamReader(context.Request.Body).ReadToEnd();
var requestData = Encoding.UTF8.GetBytes(requestBody);
context.Request.Body = new MemoryStream(requestData);
var apiPacket = new ApiPacket
{
CallerIdentity = identity,
Request = requestBody,
RequestLength = context.Request.Body.Length
};
// Buffer the response
var responseBuffer = new MemoryStream();
var responseStream = context.Response.Body;
context.Response.Body = responseBuffer;
// add the "http-tracking-id" response header so the user can correlate back to this entry
var responseHeaders = (IDictionary<string, string[]>)environment["owin.ResponseHeaders"];
responseHeaders["http-tracking-id"] = new[] { apiPacket.TrackingId.ToString("d") };
await _next.Invoke(environment);
responseBuffer.Seek(0, SeekOrigin.Begin);
var reader = new StreamReader(responseBuffer);
apiPacket.Response = await reader.ReadToEndAsync();
apiPacket.ResponseLength = context.Response.ContentLength ?? 0;
WriteRequestHeaders(context.Request, apiPacket);
WriteResponseHeaders(context.Response, apiPacket);
// You need to do this so that the response we buffered is flushed out to the client application.
responseBuffer.Seek(0, SeekOrigin.Begin);
await responseBuffer.CopyToAsync(responseStream);
//TODO: persist the ApiPacket in the database
}
private static void WriteRequestHeaders(IOwinRequest request, ApiPacket packet)
{
packet.Verb = request.Method;
packet.RequestUri = request.Uri;
packet.RequestHeaders = "{\r\n" + string.Join(Environment.NewLine, request.Headers.Select(kv => "\t" + kv.Key + "=" + string.Join(",", kv.Value))) + "\r\n}";
}
private static void WriteResponseHeaders(IOwinResponse response, ApiPacket packet)
{
packet.StatusCode = response.StatusCode;
packet.ReasonPhrase = response.ReasonPhrase;
packet.ResponseHeaders = "{\r\n" + string.Join(Environment.NewLine, response.Headers.Select(kv => "\t" + kv.Key + "=" + string.Join(",", kv.Value))) + "\r\n}";
}
}
I'm using log4net to write the information to a SQL2012 database. Both ways accomplish my goal. However, I'm looking for a reason to use one method over the other. Should I use custom OWIN middleware OR a MessageHandler, and why? Thanks in advance.
Since you already have the MessageHandler implementations, I would recommend using that until you have a reason otherwise.
However, off the top of my head one valid reason to move logging to an OwinMiddleware would be if you have other OwinMiddleware components that require (or would benefit from) that logging functionality (assuming that you are using WebApi whereby the MessageHandlers will run after all of the OwinMiddleware in the request-pipeline).
Looks like I will be using OWIN middleware. I found that inside the MessageHandler the Principal.IIdentity has not yet been resolved. For example, if I put breakpoints in my message handler, an API controller's constructor, and in the API method, this is what I see (in order).
Using Message Handler
In MessageHandler > Principal.IIdentity not yet resolved.
In API controller's constructor > Principal.IIDentity not yet resolved.
In API controller's GET method, the Principal.IIdentity is finally resolved.
Thus, I can't pull out and log the authorized user's id in the MessageHandler.
However, when using the OWIN middleware, the Principal.IIdentity IS resolved there, so I can write the userId to my log table at that point. This is why I've decided to use the middleware.
Maybe someone can provide some clarity as to when the IIDentity is set in an API project though.
I'm trying to retrieve user data from Parse (xamarin.ios using c#). I'm using an async method with await. My challenge is,each time I navigate to the tableView in the app, which should populate the user data in question,the table is always empty.
I would like to wait until the results have been returned before proceeding with the other portion of code.I have tried to use the ContinueWith() function but constantly ran into a build error -
Cannot implicitly convert type 'void' to System.Collections.Generic.IEnumerable<Parse.ParseObject>
My Questions:
Is this the best way to wait for the result?
How do I solve the build error?
Here is my current implementation:
public async void retrieveData(string username)
{
try
{
this.requests.ClearRequests();
refreshed = false;
var query = ParseObject.GetQuery("Requests").WhereEqualTo("username", username);
IEnumerable<ParseObject> results = await query.FindAsync().ContinueWith(t =>{
if(results != null)
{
foreach(ParseObject parseObject in results)
{
UserRequest request = new UserRequest();
request.objectId = parseObject.ObjectId;
request.make = parseObject.Get<string> ("item1");
request.model = parseObject.Get<string> ("item2");
request.year = parseObject.Get<string> ("item3");
request.userName = parseObject.Get<string> ("username");
this.requests.addRequest (request);
}
refreshed = true;
}
});
}
catch(ParseException e) {
Console.WriteLine (e.Message + e.StackTrace);
}
}
You shouldn't need a ContinueWith...that's what the await should handle.
await waits on a Task and then brings back the result with the proper return type. ContinueWith returns a Task, so you would have to grab the Result from the task to make it usable.
For more on this type of thing, you may want to check out Difference between await and ContinueWith
You can try something like this.
public async void retrieveData(string username, )
{
try
{
this.requests.ClearRequests();
refreshed = false;
var query = ParseObject.GetQuery("Requests").WhereEqualTo("username", username);
IEnumerable<ParseObject> results = await query.FindAsync();
if(results != null)
{
foreach(ParseObject parseObject in results)
{
UserRequest request = new UserRequest();
request.objectId = parseObject.ObjectId;
request.make = parseObject.Get<string> ("item1");
request.model = parseObject.Get<string> ("item2");
request.year = parseObject.Get<string> ("item3");
request.userName = parseObject.Get<string> ("username");
this.requests.addRequest (request);
}
refreshed = true;
}
//This is your refresh method for your TableView
this.RefreshTableView();
//or, if in iOS
NSNotificationCenter.DefaultCenter.PostNotificationName("resultsRetrieved", null);
}
catch(ParseException e) {
Console.WriteLine (e.Message + e.StackTrace);
}
}
To show the results in the tableView, I would recommend moving the refreshing of the tableView to a separate method that gets triggered synchronously after the results have been retrieved and parsed. This is shown with the this.RefreshTableView() call above.
If in iOS on Xamarin, another option is to post a notification to the NSNotificationCenter (the Xamarin documentation for which is here). Use the PostNotificationName part seen above instead and then add an observer in the ViewControllers that you want to be dependent on the data. This is done as follows:
Make a notificationToken object:
NSObject notificationToken;
Then in your setup method (you could put this inside of your ViewDidLoad):
void Setup ()
{
notificationToken = NSNotificationCenter.DefaultCenter.AddObserver ("resultsRetrieved", RefreshData);
}
Make your RefeshData method:
void RefreshData (NSString notifString)
{
this.tableView.ReloadData();
}
And then, make sure you dispose of the notification observer when you tear down the class
void Teardown ()
{
NSNotificationCenter.DefaultCenter.RemoveObserver (notificationToken);
}
I had a similar issue so started using callbacks. I'm using them in Xamarin.Android, pretty sure they're available in Xamarin.iOS.
Method that starts the task method - Note I am passing in a method of this class as a parameter
private async void updatedData()
{
await Utils.DataTasks.getNewLiveTips(populateTipsList);
}
Method that calls for data from server
public class DataTasks
{
public static async Task getAllData(Action<IEnumerable<ParseObjects>> callback) {
var query = new ParseQuery<ParseObjects>().OrderByDescending("updatedAt").Limit(5);
IEnumerable<ParseObjects> parseTips = await query.FindAsync();
foreach (var tip in parseTips)
{
// Save data to DB if needed
}
callback(parseTips);
}
Method I passed as parameter in the first instance is now called
private void populateTipsList(IEnumerable<ParseObjects> results)
{
mAdapter = new TipAdapter(this.Activity, results);
mRecyclerView.SetAdapter(mAdapter);
refresher.Refreshing = false;
}
I structured my project into multiple mobile services, grouped by the application type eg:
my-core.azure-mobile.net (user, device)
my-app-A.azure-mobile.net (sales, order, invoice)
my-app-B.azure-mobile.net (inventory & parts)
I'm using custom authentication for all my services, and I implemented my own SSO by setting the same master key to all 3 services.
Things went well when I tested using REST client, eg. user who "logged in" via custom api at my-core.azure-mobile.net is able to use the returned JWT token to access restricted API of the other mobile services.
However, in my xamarin project, only the first (note, in sequence of creation) MobileServiceClient object is working properly (eg. returning results from given table). The client object are created using their own url and key respectively, and stored in a dictionary.
If i created client object for app-A then only create for app-B, I will be able to perform CRUD+Sync on sales/order/invoice entity, while CRUD+Sync operation on inventory/part entity will just hang there. The situation is inverse if I swap the client object creation order.
I wonder if there is any internal static variables used within the MobileServiceClient which caused such behavior, or it is a valid bug ?
=== code snippet ===
public class AzureService
{
IDictionary<String, MobileServiceClient> services = new Dictionary<String, MobileServiceClient>();
public MobileServiceClient Init (String key, String applicationURL, String applicationKey)
{
return services[key] = new MobileServiceClient (applicationURL, applicationKey);
}
public MobileServiceClient Get(String key)
{
return services [key];
}
public void InitSyncContext(MobileServiceSQLiteStore offlineStore)
{
// Uses the default conflict handler, which fails on conflict
// To use a different conflict handler, pass a parameter to InitializeAsync.
// For more details, see http://go.microsoft.com/fwlink/?LinkId=521416
var syncHandler = new MobileServiceSyncHandler ();
foreach(var client in services) {
client.Value.SyncContext.InitializeAsync (offlineStore, syncHandler);
}
}
public void SetAuthenticationToken(String uid, String token)
{
var user = new MobileServiceUser(uid);
foreach(var client in services) {
client.Value.CurrentUser = user;
client.Value.CurrentUser.MobileServiceAuthenticationToken = token;
}
}
public void ClearAuthenticationToken()
{
foreach(var client in services) {
client.Value.CurrentUser = null;
}
}
}
=== more code ===
public class DatabaseService
{
public static MobileServiceSQLiteStore LocalStore = null;
public static string Path { get; set; }
public static ISet<IEntityMappingProvider> Providers = new HashSet<IEntityMappingProvider> ();
public static void Init (String dbPath)
{
LocalStore = new MobileServiceSQLiteStore(dbPath);
foreach(var provider in Providers) {
var types = provider.GetSupportedTypes ();
foreach(var t in types) {
JObject item = null;
// omitted detail to create JObject using reflection on given type
LocalStore.DefineTable(tableName, item);
}
}
}
}
=== still code ===
public class AzureDataSyncService<T> : IAzureDataSyncService<T>
{
public MobileServiceClient ServiceClient { get; set; }
public virtual Task<List<T>> GetAll()
{
try
{
var theTable = ServiceClient.GetSyncTable<T>();
return theTable.ToListAsync();
}
catch (MobileServiceInvalidOperationException msioe)
{
Debug.WriteLine("GetAll<{0}> EXCEPTION TYPE: {1}, EXCEPTION:{2}", typeof(T).ToString(), msioe.GetType().ToString(), msioe.ToString());
}
catch (Exception e)
{
Debug.WriteLine("GetAll<{0}> EXCEPTION TYPE: {1}, EXCEPTION:{2}", typeof(T).ToString(), e.GetType().ToString(), e.ToString());
}
List<T> theCollection = Enumerable.Empty<T>().ToList();
return Task.FromResult(theCollection);
}
}
=== code ===
public class UserService : AzureDataSyncService<User>
{
}
public class PartService : AzureDataSyncService<Part>
{
}
const string coreApiURL = #"https://my-core.azure-mobile.net/";
const string coreApiKey = #"XXXXX";
const string invApiURL = #"https://my-inventory.azure-mobile.net/";
const string invApiKey = #"YYYYY";
public async void Foo ()
{
DatabaseService.Providers.Add (new CoreDataMapper());
DatabaseService.Providers.Add (new InvDataMapper ());
DatabaseService.Init (DatabaseService.Path);
var coreSvc = AzureService.Instance.Init ("Core", coreApiURL, coreApiKey);
var invSvc = AzureService.Instance.Init ("Inv", invApiURL, invApiKey);
AzureService.Instance.InitSyncContext (DatabaseService.LocalStore);
AzureService.Instance.SetAuthenticationToken("AAA", "BBB");
UserService.Instance.ServiceClient = coreSvc;
PartService.Instance.ServiceClient = invSvc;
var x = await UserService.GetAll(); // this will work
var y = await PartService.GetAll(); // but not this
}
It's ok to use multiple MobileServiceClient objects, but not with the same local database. The offline sync feature uses a particular system tables to keep track of table operations and errors, and it is not supported to use the same local store across multiple sync contexts.
I'm not totally sure why it is hanging in your test, but it's possible that there is a lock on the local database file and the other sync context is waiting to get access.
You should instead use different local database files for each service and doing push and pull on each sync context. With your particular example, you just need to move LocalStore out of DatabaseService and into a dictionary in AzureService.
In general, it seems like an unusual design to use multiple services from the same client app. Is there a particular reason that the services need to be separated from each other?
I'm developing a win phone 8 app using portable version of mvvmlight.
In the creation of a ViewModel I have to do a call to a service that read data from a Azure Mobile Service using the Azure Mobile Service Sdk.
Sdk apis use async /await to do the work, and I can't do async calls in the ViewModel or in Service costructor.
The code is like this:
public ListaArtiModel(INavigate navigationService)
{
_navigationService = navigationService;
ArtiMarzialiService artiService = new ArtiMarzialiService();
List<ArteMarziale>risultato = await artiService.ListaArti();
}
and the compiler tells
Error 1 The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task'.
How can I solve this?
thanks,
Luca
I have a "task notifier" type in my AsyncEx library that is essentially an INotifyPropertyChanged wrapper for Task<T>. You can use it like this:
public ListaArtiModel(INavigate navigationService)
{
_navigationService = navigationService;
ArtiMarzialiService artiService = new ArtiMarzialiService();
Arti = NotifyTaskCompletion.Create(LoadArti(artiService));
}
private async Task<ObservableCollection<ArtiMarziali>> LoadArti(ArtiMarzialiService artiService)
{
return new ObservableCollection<ArtiMarziali>(await artiService.ListaArti());
}
public INotifyTaskCompletion<ObservableCollection<ArtiMarziali>> Arti { get; private set; }
Then your databinding code can use Arti.Result, Arti.IsFaulted, Arti.ErrorMessage, etc.
You should redesign your ViewModel to have a LoadDataAsync() or InitializeAsync() method that is used to set up the ViewModel
In general, class constructors should be kept as simple as possible and you should avoid doing any long running or potentially exception-prone work in the constructor
I think i found a better solution:
declared the service interface this way:
void ListaArti(Action<List<ArtiMarziali>, Exception> callback);
implemented it this way:
public async void ListaArti(Action<List<ArtiMarziali>, Exception> callback)
{
Exception err = null;
List<ArtiMarziali> risultato = null;
try
{
risultato = await MobileService.GetTable<ArtiMarziali>().ToListAsync();
}
catch (Exception ex)
{
err = ex;
}
callback(risultato, err);
}
called the service in the viewmodel constructor this way:
IArtiMarzialiService artiService = new ArtiMarzialiService();
artiService.ListaArti((arti, err) =>
{
if (err != null)
{
/// if there is an error should create a property and bind to it for better practices
System.Diagnostics.Debug.WriteLine(err.ToString());
}
else
{
/// set the property
Arti = new ObservableCollection<ArtiMarziali>(arti);
}
});
using an async function that returns a void I don't have to use the await statement in the caller, and I use the callback to set the property in the viewmodel when the data are available.