Cannot access a disposed object. A common cause of this error is disposing a context

Question

I have written a simple application and when I navigate to my edit page the below error pops up.

Microsoft.EntityFrameworkCore.Query[10100]

<

Answer 1

This is because of your method return type async void. In general, when you are using async void in your code it’s bad news, because:

• You can’t wait for its completion
• Any unhandled exceptions will terminate your process (ouch!)

So return async Task instead of async void from your method as follows:

public async Task OnGet(int id)
{
    Book = await _db.Books.SingleOrDefaultAsync(x => x.Id == id);

    if(Book == null)
    {
       RedirectToPage("Index");
    }
}

For more details:

• C# – beware of async void in your code

• Cannot access a disposed object in ASP.NET Core when injecting DbContext

Answer 2

This is another anwser for who gonna read this topic.

I tried to trigger asnyc method with javascript. Because of that it can't triggered and so result didn't calculated by async method. I was returning json object to view like this in dotnet core mvc.

return Json(_service.AsyncMethod(parameter));

My IActionResult is not async so I can't add "await". I just add ".Result" and it calculate result.

return Json(_service.AsyncMethod(parameter).Result);

Answer 3

What I am about to post is NOT the answer to this particular question. But it is related so just to save somebody headache I am posting it. I was encountering this same error

System.ObjectDisposedException: Cannot access a disposed object. etc

The following was the code with the bug (can you see it?):

[HttpGet("processs/oxxo-spei/ticket-email/{paymentIdx}")]
public StatusCodeResult ProcessOxxoSpeiTicketEmailAsync(string paymentIdx)
{
    var paymentId = paymentIdx.DecodeRef();
            
    var response = _orderEngine.ProcessOxxoSpeiTicketEmailAsync(paymentId);

    return StatusCode(200);
}

The following change fixed it:

[HttpGet("processs/oxxo-spei/ticket-email/{paymentIdx}")]
public async Task<StatusCodeResult> ProcessOxxoSpeiTicketEmailAsync(string paymentIdx)
{
    var paymentId = paymentIdx.DecodeRef();
            
    var response = await _orderEngine.ProcessOxxoSpeiTicketEmailAsync(paymentId);
                // ^^^^I HAD FORGOTTEN TO PUT AWAIT
    return StatusCode(200);
}

Yes that's right I had forgotten to put "await" before a function that used an EF Core dbcontext. Adding 'await' fixed it. So easy to miss it, especially if you're tired and under deadline.

Answer 4

Here is what actually worked for me in a situation where I was getting the same error as above when trying to access the data in Startup.cs to run some startup data building functions on server load, rather than a specific Controller action:

        IServiceScope scope = provider.CreateScope();
        YourDbContext context = scope.ServiceProvider.GetRequiredService<YourDbContext>();

In the Configure method of Startup.cs, with IServiceProvider included as a parameter:

public async void Configure(IApplicationBuilder app, IWebHostEnvironment env, IServiceProvider provider)

Just including that for anyone who wants to do the same in Startup.cs.