Blazor with efcore proxies crash.

[alextech]

Related to #10448

Minimal reproduceable project based on blazor template at: https://github.com/alextech/sample_use_proxy_blazor

Here, the issue is using proxies in efcore with blazor. If an object is passed to a sub-component that is accessing entity property sometime after the page has been loaded, context may have already been disposed.

Lazy Loading Proxies are needed to avoid cartesian explosion in master/detail style user interfaces, where each entity in main list has its own sublist of owned entities, that in turn, have their own joins.

Unhandled exception rendering component: Error generated for warning 'Microsoft.EntityFrameworkCore.Infrastructure.LazyLoadOnDisposedContextWarning': An attempt was made to lazy-load navigation property 'Description' on entity type 'WeatherForecastProxy' after the ass
ociated DbContext was disposed. This exception can be suppressed or logged by passing event ID 'CoreEventId.LazyLoadOnDisposedContextWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.
System.InvalidOperationException: Error generated for warning 'Microsoft.EntityFrameworkCore.Infrastructure.LazyLoadOnDisposedContextWarning': An attempt was made to lazy-load navigation property 'Description' on entity type 'WeatherForecastProxy' after the associated DbCon
text was disposed. This exception can be suppressed or logged by passing event ID 'CoreEventId.LazyLoadOnDisposedContextWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.
   at Microsoft.EntityFrameworkCore.Diagnostics.EventDefinition`2.Log[TLoggerCategory](IDiagnosticsLogger`1 logger, WarningBehavior warningBehavior, TParam1 arg1, TParam2 arg2)
   at Microsoft.EntityFrameworkCore.Diagnostics.CoreLoggerExtensions.LazyLoadOnDisposedContextWarning(IDiagnosticsLogger`1 diagnostics, DbContext context, Object entityType, String navigationName)
   at Microsoft.EntityFrameworkCore.Internal.LazyLoader.ShouldLoad(Object entity, String navigationName, NavigationEntry& navigationEntry)
   at Microsoft.EntityFrameworkCore.Internal.LazyLoader.Load(Object entity, String navigationName)
   at Microsoft.EntityFrameworkCore.Proxies.Internal.LazyLoadingInterceptor.Intercept(IInvocation invocation)
   at Castle.DynamicProxy.AbstractInvocation.Proceed()
   at Castle.Proxies.WeatherForecastProxy.get_Description()
   at sample_use_proxy.Pages.WeatherDetails.BuildRenderTree(RenderTreeBuilder __builder)
   at Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__6_0(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()
fail: Microsoft.AspNetCore.Components.Server.Circuits.CircuitHost[111]
      Unhandled exception in circuit 'iorggCZTbXKkp2XYKgVSJ7gAX9Zh3gJzhaCLmA6fiJE'.
System.InvalidOperationException: Error generated for warning 'Microsoft.EntityFrameworkCore.Infrastructure.LazyLoadOnDisposedContextWarning': An attempt was made to lazy-load navigation property 'Description' on entity type 'WeatherForecastProxy' after the associated DbCon
text was disposed. This exception can be suppressed or logged by passing event ID 'CoreEventId.LazyLoadOnDisposedContextWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.
   at Microsoft.EntityFrameworkCore.Diagnostics.EventDefinition`2.Log[TLoggerCategory](IDiagnosticsLogger`1 logger, WarningBehavior warningBehavior, TParam1 arg1, TParam2 arg2)
   at Microsoft.EntityFrameworkCore.Diagnostics.CoreLoggerExtensions.LazyLoadOnDisposedContextWarning(IDiagnosticsLogger`1 diagnostics, DbContext context, Object entityType, String navigationName)
   at Microsoft.EntityFrameworkCore.Internal.LazyLoader.ShouldLoad(Object entity, String navigationName, NavigationEntry& navigationEntry)
   at Microsoft.EntityFrameworkCore.Internal.LazyLoader.Load(Object entity, String navigationName)
   at Microsoft.EntityFrameworkCore.Proxies.Internal.LazyLoadingInterceptor.Intercept(IInvocation invocation)
   at Castle.DynamicProxy.AbstractInvocation.Proceed()
   at Castle.Proxies.WeatherForecastProxy.get_Description()
   at sample_use_proxy.Pages.WeatherDetails.BuildRenderTree(RenderTreeBuilder __builder)
   at Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__6_0(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

[pranavkm]

Hi @alextech, have a look at https://docs.microsoft.com/en-us/aspnet/core/blazor/dependency-injection?view=aspnetcore-3.1#utility-base-component-classes-to-manage-a-di-scope. Use this type to manage the lifetime of your EF context rather than creating and disposing it as part of your component initialization.

[alextech]

Thanks for reply!

Assuming I did it correctly at alextech/sample_use_proxy_blazor@8d86100

it puts me back to "second operation started on this context..."

[pranavkm]

it puts me back to "second operation started on this context..."

That error doesn't sound like it's specific to Blazor though. I'd suggest following up on StackOverflow for patterns that work well.

[alextech]

I can try stackoverflow or experts-exchane, though, this is in response to the linked issue that was collecting usecases of efcore usage with blazor.
Does this mean lazy-loading proxies are not intended to be used at all with blazor?

Discussing the issue at https://stackoverflow.com/questions/59569248/using-efcore-lazy-loading-proxies-with-blazor

[ghost]

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