EF Core: Une exception s'est produite dans la base de données lors de l'itération des résultats d'une requête

Question

Je reçois cette erreur de mon application Web hébergée dans Azure. Il fonctionne bien pendant quelques jours et s'arrête soudainement de fonctionner.

Y a-t-il un problème avec la connexion? Quelle référence d'objet n'a pas d'instance?

YYYY-MM-DD hh:mm:ss [Error] An exception occurred in the database while iterating the results of a query. 
System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.EntityFrameworkCore.Query.Internal.AsyncQueryingEnumerable.AsyncEnumerator.<BufferAllAsync>d__12.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.GetResult() at Microsoft.EntityFrameworkCore.Query.RelationalQueryContext.<RegisterValueBufferCursorAsync>d__14.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.GetResult() at Microsoft.EntityFrameworkCore.Query.Internal.AsyncQueryingEnumerable.AsyncEnumerator.<BufferlessMoveNext>d__9.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at Microsoft.EntityFrameworkCore.Query.Internal.AsyncQueryingEnumerable.AsyncEnumerator.<MoveNext>d__8.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.SelectAsyncEnumerable`2.SelectAsyncEnumerator.<MoveNext>d__4.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.<_FirstOrDefault>d__82`1.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at Microsoft.EntityFrameworkCore.Query.Internal.TaskResultAsyncEnumerable`1.Enumerator.<MoveNext>d__3.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.SelectAsyncEnumerable`2.SelectAsyncEnumerator.<MoveNext>d__4.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.<MoveNext>d__5.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at MyProject.Data.SectionRepository.<GetByTypePathAndAlias>d__6.MoveNext() in /Users/webaccount/myproject/src/MyProject.Data/Repositories/SectionRepository.cs:line 34 

Il n'y a rien de spécial dans mon référentiel ou code d'entité.

public async Task<Section> GetByTypeId(string typeId) 
{ 
    var sections = from s in this.DbContext.Sections 
     where s.TypeId == typeId 
     select s; 

    return await sections.FirstOrDefaultAsync(); // <-- LINE 34 
} 

Ceci est mon entité.

public class Section 
{ 
     [Key] 
     public int Id { get; set; } 
     public DateTimeOffset CreatedDate { get; set; } 
     public string TypeId { get; set; } 
     public string Name { get; set; } 
     public string Description { get; set; } 
} 

Est-ce lié à cela peut-être? https://github.com/aspnet/EntityFrameworkCore/issues/8026

Est-ce que ça va être utile si je convertis mes méthodes de dépôt en synchronisation et reste asynchrone au contrôleur?

Answer 1

It runs ok for a few days and then suddenly stops working.

Object reference not set to an instance of an object

Tout d'abord, vous pouvez essayer de remote debug your web app et vérifier le this.DbContext.

Deuxièmement, vous pouvez créer/utiliser une instance de contexte par requête, et this artciel shows some general guidelines when deciding on the lifetime of the context, vous pouvez le vérifier.