In my ASP.NET Web API application, I get the following error in one of my actions, at the line below:
var dateExists = await _unitOfWork.GetRepository<Booking>().All()
.AnyAsync(b => b.User.UserName == booking.User.UserName && b.Date == model.Date);
Here's the error:
A second operation started on this context before a previous
asynchronous operation completed. Use 'await' to ensure that any
asynchronous operations have completed before calling another method
on this context. Any instance members are not guaranteed to be thread
safe.
But, as you can see, I am using await. I'm also using await on all the other async operations in the action. Then, what might be the problem?
Edit:
Here's my entire action:
[HttpPut]
[Route("Update")]
public async Task<IHttpActionResult> Put(BookingEditBindingModel model)
{
if (!ModelState.IsValid)
{
// Return a bad request response if the model state is invalid...
return BadRequest(ModelState);
}
try
{
var booking = await _unitOfWork.GetRepository<Booking>().FindAsync(model.BookingId);
if (booking == null)
{
return NotFound();
}
// Only Admin is allowed to update other users' data...
if (!User.IsInRole("Admin") && booking.User.UserName != User.Identity.Name)
{
return Unauthorized();
}
// There can only be one entry per date/user.
if (model.Date != booking.Date)
{
var dateExists = await _unitOfWork.GetRepository<Booking>().All()
.AnyAsync(b => b.User.UserName == booking.User.UserName && b.Date == model.Date);
if (dateExists)
{
ModelState.AddModelError("Date", "Data already exists for this date.");
return BadRequest(ModelState);
}
}
booking.Date = model.Date;
// Change other properties...
await _unitOfWork.SaveAsync();
return Ok();
}
catch (Exception ex)
{
return InternalServerError(ex);
}
}
Update:
I disabled lazy loading, but I still had a problem. It looks like, as other people had guessed, the issue was with booking.User, because the FindAsync() in the first query does not include the User. I replaced the first query with the one below, and the issue was resolved.
var booking = await _unitOfWork.GetRepository<Booking>().All()
.Include(b => b.User)
.SingleOrDefaultAsync(b => b.BookingId == model.BookingId);
I am going to go out on a limb and guess that you have lazy loading enabled. This would cause a call like booking.User.UserName to go to the database to retrieve the value and putting that inside of a call like AnyAsync could cause the DbContext to try to open a second connection to retrieve that value after it already opened one for the AnyAsync statement.
The quick fix in this case is to retrieve the user name before the call to AnyAsync.
var bookingUserName = booking.User.UserName;
var dateExists = await _unitOfWork.GetRepository<Booking>().All()
.AnyAsync(b => b.User.UserName == bookingUserName && b.Date == model.Date);
A better fix would be to retrieve this information in advance in the call where you get the booking instance so you do not have to make an additional round trip.
Personally I always disable lazy loading on my DbContext types and use Include statements to explicitly specify what I want to be retrieved with any call. This gives me more control over my execution.
Related
I'm working on a game, where players can get points, and players can earn points that are saved in my database. I have one method that looks like this:
private async Task SendAnswer(Answer answer)
{
clicked = true;
answerText = answer.AnswerText;
team = await gameRepo.GetTeamByNameAndGameSession(Teamname, GameSessionId);
if (answer.isCorrect)
{
team.TeamPoints = team.TeamPoints + answer.Points;
}
team.Answer = answer;
await gameRepo.UpdateTeam(team);
if (hubConnection is not null)
{
await hubConnection.SendAsync("SendTeamAnswer", team, GameSessionId);
}
}
That one works just fine, but then I also have this one in another view:
private async Task ChooseBestAnswer(Team team)
{
var answer = currentQuestion.Answers.FirstOrDefault();
team.TeamPoints = team.TeamPoints + answer.Points;
await gameRepo.UpdateTeam(team);
}
Both of them uses this method
public async Task UpdateTeam(Team teamToUpdate)
{
var oldTeam = await _context.Teams.FirstOrDefaultAsync(t => t.TeamName == teamToUpdate.TeamName && t.GameSessionGuid == teamToUpdate.GameSessionGuid);
if (teamToUpdate is not null)
{
oldTeam = teamToUpdate;
}
_context.SaveChangesAsync();
}
In the first method everything works as it should but at the second "oldteam" suddenly returns that points = 0 although I can see in the database that it is not 0, how is this possible, I use the same method put it fetches a 0 where there isn't any. All the other variables that are returned from the db to "oldteam" are correct it is just the points that suddenly are zero.
Does anyone know what is going on?
A couple of problems with this code:
public async Task UpdateTeam(Team teamToUpdate)
{
var oldTeam = await _context.Teams.FirstOrDefaultAsync(t => t.TeamName == teamToUpdate.TeamName && t.GameSessionGuid == teamToUpdate.GameSessionGuid);
if (teamToUpdate is not null)
{
oldTeam = teamToUpdate;
}
_context.SaveChangesAsync();
}
As mentioned in the comments, the SaveChangesAsync isn't awaited, but more importantly, this code doesn't update the team in the database. You are loading the existing team, but then simply overwriting the in-memory reference. That doesn't copy values across. Instead:
public async Task UpdateTeam(Team teamToUpdate)
{
if (teamToUpdate == null) throw new NullReferenceException(nameof(teamToUpdate));
var existingTeam = await _context.Teams.SingleAsync(t => t.TeamName == teamToUpdate.TeamName && t.GameSessionGuid == teamToUpdate.GameSessionGuid);
existingTeam.TeamPoints = teamToUpdate.TeamPoints;
// copy any additional fields that are allowed to be updated.
await _context.SaveChangesAsync();
}
Key changes to consider here. Assert the passed in state early and handle if it's invalid. If you expect 1 team to be found, use Single rather than First, and if an entry is expected, don't use the OrDefault variations. Those should be used only if you expect that an item might not be found. Once we have the existing data record, copy the values that can change across and call SaveChanges, awaiting the async operation.
This code will throw exceptions if expected state isn't valid, but it will throw meaningful exceptions to be handled at an appropriate level. (Rather than less descriptive exceptions when assumptions aren't met, or failing silently.)
I'm trying to update my UserRoles table but it won't update. I'm trying to update two things : 1. the email 2. the user role. Because the update needs to happen in 2 tables I'm using two separate commands. When I run the update on the Email alone (Users) it works but if I update the role (AspUserRoles) it does nothing. When I run it both it doesn't work either because UserRoles.Attach(userRole) is preventing it from updating. I also get no errors.
I checked if ApplicationRole.Id and ApplicationUser.Id has a value and it does return the value I want.
Here's my UserController.cs :
public async Task<IActionResult> Edit(UserViewModel model, Guid id)
{
var alert = new Alert();
try
{
if(!ModelState.IsValid)
{
alert.Message = alert.ExceptionMessage = ApplicationDbContextMessage.INVALID;
throw new Exception();
}
var originalModel = ApplicationDbContext.Users.FirstOrDefault(u => u.Id == id);
var userRole = ApplicationDbContext.UserRoles.FirstOrDefault(i => i.UserId == id);
if(originalModel == null)
{
alert.Message = alert.ExceptionMessage = ApplicationDbContextMessage.NOTEXISTS;
throw new Exception();
}
originalModel.Email = model.ApplicationUser.Email;
userRole.RoleId = model.ApplicationRole.Id;
ApplicationDbContext.Users.Attach(originalModel);
ApplicationDbContext.UserRoles.Attach(userRole);
ApplicationDbContext.Entry(originalModel).State = EntityState.Modified;
if (await ApplicationDbContext.SaveChangesAsync() == 0)
{
alert.Message = alert.ExceptionMessage = ApplicationDbContextMessage.EDITNOK;
throw new Exception();
}
alert.Message = ApplicationDbContextMessage.EDITOK;
return RedirectToAction("Index");
}
catch(Exception ex)
{
alert.Type = AlertType.Error;
alert.ExceptionMessage = ex.Message;
model = await ViewModel(model.ApplicationUser);
ModelState.AddModelError(string.Empty, alert.ExceptionMessage);
}
return View(model);
}
The way you are modifying data in this code, you don't need to call Attach or Add on the Context to let it know about changes to entities, that will happen automatically.
From the moment you pull an entity out of a DbSet of the DbContext it is being tracked (attached) by that DbContext. When you call SaveChanges on the DbContext it will scan any entities that it is tracking, comparing current values to old values, to find changes. Those changes then get sent to the data base.
You should literally be able to remove 3 lines of code from what you originally posted and have it work.
...
originalModel.Email = model.ApplicationUser.Email;
userRole.RoleId = model.ApplicationRole.Id;
ApplicationDbContext.Users.Attach(originalModel); // <--- Delete this line
ApplicationDbContext.UserRoles.Attach(userRole); // <--- Delete this line
ApplicationDbContext.Entry(originalModel).State = EntityState.Modified; // <--- Delete this line
if (await ApplicationDbContext.SaveChangesAsync() == 0)
...
A little something else I noticed. It looks like you might be using one single DbContext instance for the entire application. That is usually considered an "Anti-Patern" in Entity Framework. You should create a new DbContext instance (with using) for every "logical" operation you perform. That instance should only be alive for the life of that operation.
In MVC, this is usually one DbContext instance per ActionMethod.
Within an ASP.NET MVC Application I'm recieving the following error message for one of my controller methods that uses my Entity Framework context.
A second operation started on this context before a previous asynchronous operation completed. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe.
I'm aware that you cannot run queries in parallel, and everything appears to be awaited properly. If I debug the program and step and inspect some of the data returned from EF then it works, probably because this forces the queries to complete.
EDIT If I place a breakpoint at the null check in the controller method and inspect the data of shipmentDetail the exception is NOT thrown.
Here's a snippit of the code:
Controller Method:
[Route("{id:int}/Deliveries")]
public async Task<ActionResult> DeliveryInfo(int id)
{
var shipmentDetail = await db.ShipmentDetails.SingleOrDefaultAsync(s => s.Id == id);
if (shipmentDetail == null)
return HttpNotFound(string.Format("No shipment detail found with id {0}", id));
var model = await DeliveryInfoModel.CreateModel(db, shipmentDetail);
return View("DeliveryInfo", model);
}
CreateModel Method:
public static async Task<DeliveryInfoModel> CreateModel(Context db, ShipmentDetail shipment)
{
DeliveryInfoModel model = new DeliveryInfoModel()
{
ShipmentInfo = shipment
};
//initialize processing dictionary
Dictionary<int, bool> boxesProcessed = new Dictionary<int, bool>();
List<DeliveryBoxStatus> statuses = new List<DeliveryBoxStatus>();
for (int i = 1; i <= shipment.BoxCount; i++ )
{
boxesProcessed.Add(i, false);
}
//work backwards through process
//check for dispositions from this shipment
if(shipment.Dispositions.Count > 0)
{
foreach (var d in shipment.Dispositions)
{
DeliveryBoxStatus status = new DeliveryBoxStatus()
{
BoxNumber = d.BoxNumber,
LastUpdated = d.Date,
Status = d.Type.GetDescription().ToUpper()
};
statuses.Add(status);
boxesProcessed[d.BoxNumber] = true;
}
}
//return if all boxes have been accounted for
if (boxesProcessed.Count(kv => kv.Value) == shipment.BoxCount)
{
model.BoxStatuses = statuses;
return model;
}
//check for deliveries
if(shipment.Job_Detail.Count > 0)
{
foreach (var j in shipment.Job_Detail.SelectMany(d => d.DeliveryInfos))
{
DeliveryBoxStatus status = new DeliveryBoxStatus()
{
BoxNumber = j.BoxNumber,
LastUpdated = j.Job_Detail.To_Client.GetValueOrDefault(),
Status = "DELIVERED"
};
statuses.Add(status);
boxesProcessed[j.BoxNumber] = true;
}
}
//check for items still in processing & where
foreach (int boxNum in boxesProcessed.Where(kv => !kv.Value).Select(kv => kv.Key))
{
//THIS LINE THROWS THE EXCEPTION
var processInfo = await db.Processes.Where(p => p.Jobs__.Equals(shipment.Job.Job__, StringComparison.InvariantCultureIgnoreCase) && p.Shipment == shipment.ShipmentNum && p.Box == boxNum)
.OrderByDescending(p => p.date)
.FirstOrDefaultAsync();
//process returned data
//...
}
model.BoxStatuses = statuses;
return model;
}
I'm not completely sure if it's because of the query made in the controller, or because of the queries made in the loop that aren't completing causing this behavior. Is there something I'm not understanding about when the queries are actually made/returned due to EF's laziness, or how async/await works in this situation? I have a lot of other methods & controllers that make async EF calls and haven't run into this previously.
EDIT
My context is injected into my controller using Ninject as my IoC container. Here's its config inside of NinjectWebCommon's RegisterServices method:
kernel.Bind<Context>().ToSelf().InRequestScope();
Avoid lazy loading when using async with Entity Framework. Instead, either load the data you need first, or use Include()'s to ensure the data you need is loaded with the query.
https://msdn.microsoft.com/en-gb/magazine/dn802603.aspx
Current State of Async Support
... Async
support was added to Entity Framework (in the EntityFramework NuGet
package) in version 6. You do have to be careful to avoid lazy
loading when working asynchronously, though, because lazy loading is
always performed synchronously. ...
(Emphasis mine)
Also:
https://entityframework.codeplex.com/wikipage?title=Task-based%20Asynchronous%20Pattern%20support%20in%20EF.#ThreadSafety
I am using the following code to update data using the MongoDB C# Driver:
public async Task<bool> UpdateFirstName(string id, string firstName)
{
await Collection.UpdateOneAsync(Builders<User>.Filter.Eq(
"_id", new ObjectId(id)),
Builders<User>.Update.Set("firstName", firstName)
.CurrentDate("lastUpdatedDate"));
}
This method returns "bool", because I want to know if the data has been updated successfully. This would be the pseudocode for checking if the data has been updated successfully:
if (data updated successfully)
{
return true;
}
else
{
return false;
}
Does anyone know how to write the code for checking if the data updated successfully? Thanks!
If the method was executed so the update was done, otherwise the method will throw an exception - In case of async it's important to not forget the await (since using async method without await can't ensure your application stay around long enough to retreive the exception)
UpdateOneAsync has a return value of UpdateResult?, which gives you access to the ModifiedCount. As you you UpdateOne a single greater 0 check is enough.
var response = await Collection.UpdateOneAsync(Builders<User>.Filter.Eq(
"_id", new ObjectId(id)),
Builders<User>.Update.Set("firstName", firstName)
.CurrentDate("lastUpdatedDate"));
if response.ModifiedCount > 0 {
// success
}
// failed
This will throw an Exception if the Update is not acknowledged.
I am not sure what to use in this scenario.
I have an asp.net web api method that basically does this
Finds points of interests from foursquare near user.
Uses the foursquare locations to do queries in my database to find unique data about point of interest near user.
However since I need to store some of the foursquare information to link to my unique data to that location I decided to store all the information in my database and have my database act as my caching system.
This means anything new point of interest that comes in I have to insert into my database, check if it exists and if so then skip it or if it exists check the last refresh date(foursquare policy states all data must be refreshed after 30 day) and if it out past the refresh date I have to update the data.
I want to slow the user down and have to wait for the above to happen. I want my code to do step 1 and then do what I just mentioned while at the same time doing step 2.
Once step 2 finishes I want to return the data and let the user get on their way. If my caching system is not finished then it should keep going but not bog down the user.
I won't use any of these new results in step 2 as if I am inserting it then I won't have any data on that location at this time.
Not sure if I need to make a thread or use the async/await to achieve this.
Edit
Here is what I am trying to do
public HttpResponseMessage Get()
{
// this will do a foursquare lookup to find all stores near the user
// I want to insert them into my database and link it to my unquie data.
// stores pulled from foursquare will
// a) Be new and not in my database
// b) exist in my database but have been refreshed lately
// c) have not been refreshed in timeframe of foursquare policy
// THIS SHOULD WORK IN THE BACKGROUND
storeService.PointsOfInterestNearUser(80, -130); //As you can see it is
//void. Not sure where to put the async/await stuff
// find this product. Should be happening at the same time as above line.
var product = productService.FindProduct("Noodles");
//This will get returned to the user.
// the new stores taht are being added in StoreNearUser
//won't effect this search as I will have not data on this new store
// if existing store is being refreshed it is possible old
//address might be picked up...
//I can live with that as I doubt the address will change much.
// this should happen after product
var allStores = storeService.FindStoresThatHaveItem(product);
// this should be returned as soon as above line is finished.
//If StoreNearUser is not done, it should keep going but not hold up user.
return allStores;
}
public void StoresNearUser(double latitude, double longitude)
{
// get all categories I can about in foursquare.
//First time from db otherwise cached.
List<StoreCategory> storeCategories = GetStoreCategories();
// do a request and get everything in near the user
//(provided it is also in a category I care about)
var request = CreateFoursquareStoreRequest
(latitude, longitude, storeCategories);
// do the actual call.
var response = client.Execute<VenueSearch>(request);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
// start going through the results, add or update or skip of entry will happen
AddUpdateStores(storeCategories, response);
}
else
{
ErrorSignal.FromCurrentContext().Raise(response.ErrorException);
}
}
Edit 2
public async Task StoresNearUser(double latitude, double longitude)
{
// get all categories I can about in foursquare. First time from db otherwise cached.
List<StoreCategory> storeCategories = GetStoreCategories();
// do a request and get everything in near the user(provided it is also in a category I care about)
var request = CreateFoursquareStoreRequest(latitude, longitude, storeCategories);
await client.ExecuteAsync<VenueSearch>
( request
, response =>
{
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
AddUpdateStores(storeCategories, response);
}
else
{
ErrorSignal.FromCurrentContext()
.Raise(response.ErrorException);
}
}
);
}
gives me this error
Cannot await 'RestSharp.RestRequestAsyncHandle'
I also don't get the difference between Task and void. From what I read if you just use Task it means you are sending nothing back of meaning, then why not just use void?
Edit 2
I found this post to show me how to make the wrapper for Restsharp. It is not 100% what I want but that is a separate issue.
public async Task StoresNearUser(double latitude, double longitude)
{
List<StoreCategory> storeCategories = GetStoreCategories();
var request = CreateFoursquareStoreRequest
(latitude, longitude, maxRadius, returnLimit, storeCategories);
var response = await client.GetResponseAsync(request);
if (response.StatusCode == HttpStatusCode.OK)
{
// had to use json.net right now as the wrapper does not expose restsharps deserilizer
var venue = JsonConvert
.DeserializeObject<VenueSearch>(response.Content);
AddUpdateStores(storeCategories, venue);
}
else
{
ErrorSignal.FromCurrentContext()
.Raise(response.ErrorException);
}
}
public async Task<HttpResponseMessage>Get()
{
await storeService.PointsOfInterestNearUser(80, -130);
var product = productService.FindProduct("Noodles");
var allStores = storeService.FindStoresThatHaveItem(product);
return allStores;
}
When I watch from the debugger it looks like it is still all going in order. I think product and allStores need to be since I need the product before I can find the stores but PointsOfInterestNearUser should be going at the same time as FindProduct.
Edit 3
Here is my FindProduct Method. Not sure what to make async to me it looks like everything needs to wait.
public ResponseResult<Product> FindProduct(string barcode)
{
ResponseResult<Product> responseResult = new ResponseResult<Product>();
Product product = null;
try
{
var findBarCode = context.Barcodes.Where(x => x.Code == barcode).Select(x => x.Product).FirstOrDefault();
responseResult.Response = product;
if (product == null)
{
responseResult.Status.Code = HttpStatusCode.NotFound;
}
else
{
responseResult.Status.Code = HttpStatusCode.OK;
}
}
catch (SqlException ex)
{
ErrorSignal.FromCurrentContext().Raise(ex);
responseResult.Status.Code = HttpStatusCode.InternalServerError;
responseResult.Status.Message = GenericErrors.InternalError;
}
return responseResult;
}
Edit 4
Still not sure how to do the Task.WhenAll()
public async Task<HttpResponseMessage>Get()
{
Task[] tasks = new Task[2];
tasks[0] = storeService.PointsOfInterestNearUser(80, -130);
tasks[1] = productService.FindProduct("Noodles");
await Task.WhenAll(tasks);
// not sure how to get product back out. I looked in the debugger and saw a "Result" that has it but when I do tasks[1].Result inetllisene cannot find .Result
var allStores = storeService.FindStoresThatHaveItem(product);
return allStores;
}
I would recommend using async/await for this. Updating a cache is one of the rare situations where returning early from an ASP.NET request is acceptable. You can see my blog post on the subject for some helpful code.
So, something like this (simplified to just look up one "interesting place" per location):
public async Task<PlaceWithData> FindPlaceAsync(Location myLocation)
{
Place place = await GetPlaceFromFoursquareAsync(myLocation);
PlaceWithData ret = await GetExtraDataFromDatabaseAsync(place);
if (ret.NeedsRefresh)
BackgroundTaskManager.Run(() => UpdateDatabaseAsync(place, ret));
return ret;
}
You may also want to consider extending the ASP.NET caching system rather than doing a "roll your own" cache.