I have seen many posts talking about the problem but none of them fixed my problem
the scenario
DB Layer with API Controllers
IDataRepository
DataManagers
Code
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddDbContext<ApplicationContext>(opts => opts.UseSqlServer(Configuration["ConnectionString:LawyerApplicationDB"]), ServiceLifetime.Transient);
services.AddSingleton(typeof(IDataRepository<Clients, long>), typeof(ClientManager));
services.AddSingleton(typeof(IDataRepository<Nationality, long>), typeof(NationalityManager));
services.AddMvc();
}
ApplicationContext
public class ApplicationContext: DbContext
{
public ApplicationContext(DbContextOptions opts) : base(opts)
{
}
public DbSet<Clients> Clients { get; set; }
public DbSet<Nationality> Nationalities { get; set; }
}
The Manager where the error Appear
public class NationalityManager : IDataRepository<Nationality, long>
{
private ApplicationContext ctx; //not static
public NationalityManager(ApplicationContext c)
{
ctx = c;
}
public Nationality Get(long id)
{
var nationality = ctx.Nationalities.FirstOrDefault(b => b.Id == id);
return nationality;
}
public IEnumerable<Nationality> GetAll()
{
var nationalities = ctx.Nationalities.ToList();
return nationalities;
}
the error appear first time and the grid does not show data if i refresh the page the data will show
what i do wrong
this is the tutorial i used Building An ASP.NET Core Application With Web API And Code First Development
Thank you for your help
You've fallen into a classic situation where you are keeping the context around too long.
Because NationalityManager is registered as a singleton it doesn't matter that your context was registered as transient. Something with a short lifetime injected into something with a long lifetime effectively means the short lifetime is extended by the lifetime of the longer lived thing.
You can either make your manager object shorter lived or you can inject a context factory into your manager. The context factory ensures your (what should be short lived) context is created when its needed.
When you have API calls coming in at the same time, they are attempting to use the non-thread safe context simultaneously. The first call is setting up the model, and then here comes another call wanting to use the model while its being setup.
Prior to EF Core, I've addressed this issue with the original EF designed for .NET Framework. It might give you some more background.
I cannot seem to find an answer to this question.
So in the frontend when the user loads a page we call an API for each item on that page (10 items). So that equals 10 API calls.
Most of the calls work but there are always a few that fail when trying to query the database resulting in the following error:
InvalidOperationException: A second operation started on this
context before a previous operation completed. Any instance members
are not guaranteed to be thread safe.
Now I understand that Entity Framework is not thread safe but I am unsure how to get around this error.
Everywhere where I am using a DBContext it is always injected in using the built in .net core Ioc container.
Here is the DI setup
services.AddScoped<IOmbiContext, OmbiContext>();
services.AddTransient<ISettingsRepository, SettingsJsonRepository>();
All of my repositories are setup in a Transient scope with the Context as Scoped according to this article: https://learn.microsoft.com/en-us/aspnet/core/data/entity-framework-6
Now I have tried changing the context to Transient and it still happens.
How can I avoid this?
More Information
The API Method:
[HttpGet("movie/info/{theMovieDbId}")]
public async Task<SearchMovieViewModel> GetExtraMovieInfo(int theMovieDbId)
{
return await MovieEngine.LookupImdbInformation(theMovieDbId);
}
Which eventually calls the following where the exception is being thrown:
public async Task<RuleResult> Execute(SearchViewModel obj)
{
var item = await PlexContentRepository.Get(obj.CustomId); <-- Here
if (item != null)
{
obj.Available = true;
obj.PlexUrl = item.Url;
obj.Quality = item.Quality;
}
return Success();
}
PlexContentRepository
public PlexContentRepository(IOmbiContext db)
{
Db = db;
}
private IOmbiContext Db { get; }
public async Task<PlexContent> Get(string providerId)
{
return await Db.PlexContent.FirstOrDefaultAsync(x => x.ProviderId == providerId); <-- Here
}
If you use Entity Framework Core usually you do not need to add your Database Context as an additional service
I recommend to setup your DbContext in the Startup.cs as following:
services.AddEntityFrameworkSqlServer()
.AddDbContext<OmbiContext>();
Followed by a Controller class for your API calls taking the DBContext as constructor parameter.
public class ApiController : Controller
{
protected OmbiContext ctx;
public ApiController(OmbiContext dbctx)
{
ctx = dbctx;
}
public async Task<IActionResult> yourAsyncAction()
{
// access ctx here
}
}
I'm implementing a Model using EF 6.1.3 and .NET Framework 4.6.1.
This model is used by an ASPNET app and by an ASPNET CORE app, for that reason it uses System.Data.Entity and it is located in a separate assembly mymodel.dll.
This is the model
using System.Data.Entity;
public partial class MyDbContext : DbContext
{
public virtual DbSet<Athlete> Athletes{ get; set; }
}
public partial class Athlete
{
public Athlete()
{
}
//...
public string Country { get; set; }
}
I'm developing the MVC app that is implemented in aspnet core with .NET Framework 4.6. It references EF 6.1.3 so that the model can be used.
public class MyViewModel
{
public IList<Athlete> ItalianAthletes{ get; set; }
}
using Microsoft.EntityFrameworkCore;
//solution: comment the previous line and use instead System.Data.Entity;
public class MyController : Controller
{
private readonly MyDbContext _context;
//...
public IActionResult Index()
{
MyViewModel myvm = new MyViewModel();
var result = _context.Athletes.Where(a=>a.Country=="Italy").ToList();
myvm.ItalianAthletes = result ;
return View(myvm);
}
}
... and it works as expected.
Now changing the Index method to async
public async Task<IActionResult> Index()
{
MyViewModel myvm = new MyViewModel();
var result = _context.Athletes.Where(a=>a.Country=="Italy").ToListAsync();
await result; //at this point an exception is thrown
//...
}
InvalidOperationException: The source IQueryable doesn't implement IAsyncEnumerable. Only sources that implement IAsyncEnumerable can be used for Entity Framework asynchronous operations.
Removing the Where() clause the problem persists, so the problem seems related to ToListAsync();
var result = _context.Users.ToListAsync();
Carefully reading the text of the exception I understand that "the IQueryable generated by ToList() doesnt implement IAsyncEnumerable " but this doesnt make sense to me because all that behavior is internal to ToListAsync();
Someone can help me to better understand what's happening here under the hood? and what can I do so that ToListAsync() works as expected ?
thank you in advance for any comment
If you are using Entity Framework Core then you have to use this namespace:
using Microsoft.EntityFrameworkCore;
instead of
using System.Data.Entity;
EF Core Solution
You need to use this using statement.
using Microsoft.EntityFrameworkCore;
EF6 Solution
You will want to do one of these 2 things.
Reference the EF nuget package in both assemblies. This is because this ToListAsync() operation is actually being called through to your EF DbContext and this cannot be done from a project that has no reference to the EF NugetPackage. If this is already the case make sure you are referencing the namespace System.Data.Entity in the using statements at the top of the code:
using System.Data.Entity;
as this is the location of the extension method ToListAsync you want to call.
Wrap the code that retrieves from EF in a service in your project that uses EF, make the call async, and call that from your asp.net mvc project. This would be my preferred choice as it adds a nice layer of abstraction and makes your code easier to test/maintain.
Code example for 2nd option
public interface IAthleteService {
Task<List<Athlete>> GetAthletesByCountryAsync(string country, CancellationToken token);
}
public class AthleteService : IAthleteService {
private MyDbContext _context;
public async Task<List<Athlete>> GetAthletesByCountryAsync(string country, CancellationToken token)
{
return await _context.Athletes.Where(athlete => athlete.Country == country).ToListAsync(token).ConfigureAwait(false);
}
}
public class MyController : Controller
{
private readonly IAthleteService _service;
//...
public async Task<IActionResult> Index(CancellationToken token)
{
MyViewModel myvm = new MyViewModel();
myvm.ItalianAthletes = await _service.GetAthletesByCountryAsync("Italy", token).ConfigureAwait(true);
// rest of code
}
}
Notes:
I used a CancellationToken, it allows for the cancellation of an async operation. This is completely optional.
I used ConfigureAwait, this allows you to specify whethere the same thread context should be recaptured when the operation resumes. It saves resources to not do it (pass false) but you can only do that when its possible. In the above example its done in the library. Also in the example above it is not done from the Controller because you need the Http context associated with the thread (pass true).
I did not take into account cleaning up of resources (like making AthleteService disposable to cleanup the DbContext) or any injection of dependencies.
This topic is old but I ran into the same error in the year 2021 for same or different reasons.
In short: Get rid of .ToListAsync() and replace it with .ToList()
I ran into this issue in my .NET5 project by using EntityFrameworkCoreMock.Moq in a unit test project and failed with this error. I asked a friend and was told to get rid of ToListAsync(). I decided to also get rid of AsyncFixer for that reason.
I'm not really happy with that solution either and hate code that fails at runtime for strange reasons in general. But that's the solution I ended up with.
On an ASP.NET Core project I have the following on Startup:
services.AddDbContext<Context>(x => x.UseSqlServer(connectionString));
services.AddTransient<IValidationService, ValidationService>();
services.AddTransient<IValidator<Model>, ModelValidator>();
The ValidationService is as follows:
public interface IValidationService {
Task<List<Error>> ValidateAsync<T>(T model);
}
public class ValidationService : IValidationService {
private readonly IServiceProvider _provider;
public ValidationService(IServiceProvider provider) {
_provider = provider;
}
public async Task<List<Error>> ValidateAsync<T>(T model) {
IValidator<T> validator = _provider.GetRequiredService<IValidator<T>>();
return await validator.ValidateAsync(model);
}
}
And the ModelValidator is as follows:
public class ModelValidator : AbstractValidator<Model> {
public ModelValidator(Context context) {
// Some code using context
}
}
When I inject a IValidationService in a controller and use it as:
List<Error> errors = await _validator.ValidateAsync(order);
I get the error:
System.ObjectDisposedException: Cannot access a disposed object. A
common cause of this error is disposing a context that was resolved
from dependency injection and then later trying to use the same
context instance elsewhere in your application. This may occur is you
are calling Dispose() on the context, or wrapping the context in a
using statement. If you are using dependency injection, you should
let the dependency injection container take care of disposing context
instances. Object name: 'Context'.
Any idea why I am having this error when using Context inside ModelValidator.
How to fix this?
UPDATE
So I changed the code to:
services.AddScoped<IValidationService, ValidationService>();
services.AddScoped<IValidator<Model>, ModelValidator>();
But I get the same error ...
UPDATE - Seed Data Code inside Configure method on Startup
So on Configure method I have:
if (hostingEnvironment.IsDevelopment())
applicationBuilder.SeedData();
And the SeedData extension is:
public static class DataSeedExtensions {
private static IServiceProvider _provider;
public static void SeedData(this IApplicationBuilder builder) {
_provider = builder.ApplicationServices;
_type = type;
using (Context context = (Context)_provider.GetService<Context>()) {
await context.Database.MigrateAsync();
// Insert data code
}
}
What am I missing?
UPDATE - A possible solution
Changing my Seed method to the following seems to work:
using (IServiceScope scope =
_provider.GetRequiredService<IServiceScopeFactory>().CreateScope()) {
Context context = _provider.GetService<Context>();
// Insert data in database
}
Just a guess in what causes your error:
You are using DI and async calls. If, somewhere in your call stack, you return a void instead of Task, you get the described behavior. At that point, the call is ended and the context disposed. So check if you have an async call that returns a void instead of Task. If you change the return value, the ObjectDisposedException is probably fixed.
public static class DataSeedExtensions {
private static IServiceProvider _provider;
public static async Task SeedData(this IApplicationBuilder builder) { //This line of code
_provider = builder.ApplicationServices;
_type = type;
using (Context context = (Context)_provider.GetService<Context>()) {
await context.Database.MigrateAsync();
// Insert data code
}
}
And in configure:
if (hostingEnvironment.IsDevelopment()){
await applicationBuilder.SeedData();
}
Blog post on how to fix this error: Cannot access a disposed object in ASP.NET Core when injecting DbContext
I had a similar issue working with asp.net core. I have an async POST method in my controller and when it returns void I will have this exception. After I changed the POST method return a TASK the problem was solved.
Change from:
public async void PostAsync([FromBody] Model yourmodel)
To
public async Task PostAsync([FromBody] Model yourmodel)
Update for ASP.NET Core 2.1
In ASP.NET Core 2.1 the methods changed slightly. The general method is similar to the 2.0, just the methods name and return types have been changed.
public static void Main(string[] args)
{
CreateWebHostBuilder(args)
.Build()
.Seed();
}
public static IWebHostBuilder CreateWebHostBuilder(string[] args)
{
return new WebHostBuilder()
...; // Do not call .Build() here
}
Applies for ASP.NET Core 2.0
With ASP.NET Core 2.0 there have been some changes in how EF Core tools (dotnet ef migrations etc.) determine the DbContext and connection string at design time.
The below answer leads that the migrations and seeding are applied when calling any of the dotnet ef xxx commands.
The new pattern for getting a design time instance for the EF Core tools is by using an BuildHostWeb static method.
As per this announcement, EF Core will now use the static BuildWebHost method which configures the whole application, but doesn't run it.
public class Program
{
public static void Main(string[] args)
{
var host = BuildWebHost(args);
host.Run();
}
// Tools will use this to get application services
public static IWebHost BuildWebHost(string[] args) =>
new WebHostBuilder()
.UseKestrel()
.UseContentRoot(Directory.GetCurrentDirectory())
.UseIISIntegration()
.UseStartup<Startup>()
.Build();
}
Replace this in your old Main method
public static void Main(string[] args)
{
var host = BuildWebHost(args)
.Seed();
host.Run();
}
Where Seed is an extension method:
public static IWebHost Seed(this IWebHost webhost)
{
using (var scope = webhost.Services.GetService<IServiceScopeFactory>().CreateScope())
{
// alternatively resolve UserManager instead and pass that if only think you want to seed are the users
using (var dbContext = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>())
{
SeedData.SeedAsync(dbContext).GetAwaiter().GetResult();
}
}
}
public static class SeedData
{
public static async Task SeedAsync(ApplicationDbContext dbContext)
{
dbContext.Users.Add(new User { Id = 1, Username = "admin", PasswordHash = ... });
}
}
Old Answer, still applies to ASP.NET Core 1.x
There is a semi-official pattern on how to seed Entity Framework Core in ASP.NET Core application you should apply, because during application startup there is no Request and hence no RequestServices (which resolves scoped services).
In essence it boils down to creating a new scope, resolve the types you need and dispose the scope again once you're finished.
// serviceProvider is app.ApplicationServices from Configure(IApplicationBuilder app) method
using (var serviceScope = serviceProvider.GetRequiredService<IServiceScopeFactory>().CreateScope())
{
var db = serviceScope.ServiceProvider.GetService<AppDbContext>();
if (await db.Database.EnsureCreatedAsync())
{
await SeedDatabase(db);
}
}
One of the reasons directly resolving a service via app.ApplicationServices.GetService<MyService>() is that ApplicationServices is the application (or lifetime) scope provider and the services resolved here stay alive until the application is shut down.
Usually the scoped container will resolve from it's parent container, if the object already exists there. So if you instantiate the DbContext this way in the application, it will be available in ApplicationServices container and when a request happens, a child container will be created.
Now when resolving the DbContext it won't be resolved as scoped, because it already exists in the parent container, so the instance of the parent container will be returned instead. But since it has been disposed during the seeding, it won't be accessible.
A scope container is nothing else then a singleton container with limited lifetime.
So never resolve scoped services in Application startup w/o using the pattern above of first creating a scope and resolving from it.
If you are using any async void please replace it with async Task
Had the same issue. Hope this helps someone. In addition to making the method async and return a Task, you need to make sure that the method will also be awaited wherever you are calling it.
the problem is that DBContext is scoped per request by default, but you have things that depend on it scoped as transient, so they do not have the same scope and DBContext may be disposed before you are done using it
Similar to Yang Zhang, I had to change my controller function
From:
public IActionResult MyFunc([FromBody]string apiKey)
To:
public async Task<IActionResult> MyFunc([FromBody]string apiKey)
I'd like to share my solution for those who are trying to start a background task in their controllers. That means you want to start a task and don't want to wait for the result like audit logging to database. If you are creating a task and try to do database operations in that task you will receive this error;
Cannot access a disposed object. A common cause of this error is disposing a context that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling Dispose() on the context, or wrapping the context in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances.\r\nObject name: 'DBContext'.
Already explained in details. Find it here
In my case, it wasn't an Async problem, but the code had a
using (DataContext dc=dataContext) {}
block, and of course, the context was disposed after that.
In my case the controller method was async and it was returning a task but inside that I had 2 await calls. First await calls gets some data from a service and second await call writes to the DB using EF. I had to remove the await from this second call and only then it worked. I didn't remove async/await from method signatures. I just called the second method without await.
I was facing a similar error and later was able to resolve it.
I was calling the async method without using await.
old code
var newUser = _repo.Register(newUserToCreate);
with the fix made
var newUser = await _repo.Register(newUserToCreate);
When interacting with the database, Entity Framework can suddenly throw an "An operation is already in progress." exception. I have done some testing by sending many concurrent requests and come to the conclusion that this is has to do with some requests sharing the same persistence context. I'm using Entity Framework Core with PostgreSQL.
This is how I've configured EF in my startup class:
services.AddEntityFramework()
.AddNpgsql()
.AddDbContext<PersistenceContext>(options =>
{
options.UseNpgsql(Configuration["Database:ConnectionString"]);
});
The PersistenceContext is a class with DbSet< ModelType > for each type that I store in the database. The PersistenceContext are injected using dependency injection. An example of a connection string I'm using now is:
Server=localhost;User Id=myUser;Password=myPasswordDatabase=myDb;
I've also tried to add a Pooling flag to the string without any affect.
An example of a simple controller for a web-API that would throw the exception:
[Route("example")]
public class FooController : Controller
{
private PersistenceContext dbContext;
public ChannelController(PersistenceContext dbContext)
{
this.dbContext = dbContext;
}
[HttpGet]
public async Task<IActionResult> GetFoo()
{
Model.Foo instance = await (from p in dbContext.Foo
select p).SingleOrDefaultAsync();
return Ok(instance);
}
}
Am I missing out on some details for setting up EF or could this be a framework bug? I'm on RC1-final.