尝试在请求管道内写入数据库时​​出现ObjectDisposedException

Question

I am trying to add some code that will save a DateTime value to database on every request.

I added some code to Configure method with app.Use() .

This is my configure method:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, MyDbContext db)
{
    var appSettings = Configuration.GetSection("AppSettings").Get<AppSettings>();

    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }            

    app.UseCors(builder =>
       builder.WithOrigins(appSettings.BaseUrls.WebAllowCors)
              .AllowAnyHeader().AllowAnyMethod()
   );

    app.UseAuthentication();


    app.Use(async (context,next) =>
    {
        var id = context.User.Claims.First(x => x.Type == "sub").Value;

        var user = db.AspNetUsers.Find(id);

        user.LastAccessed = DateTime.Now;

        await db.SaveChangesAsync();

        await next();
    });

    app.UseMvc();
}

But I get the error:

An unhandled exception occurred while processing the request.

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 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. Object name: 'MyDbContext'.

What is correct way here to write to database on every request?

Answer 1

this can happen because you are using the scope wrong. You are getting the db instance from your configure method. But this is called once at the startup.

You should do something like this:

  app.Use(async (context, next) =>
        {
            var id = context.User.Claims.First(x => x.Type == "sub").Value;
            using(var db = context.RequestServices.GetService<MyDbContext>())
            {

               var user = db.AspNetUsers.Find(id);

               user.LastAccessed = DateTime.Now;

               await db.SaveChangesAsync();
            }
            await next();
        });

Hope this snippet helps you. If you need any clarification i would be more than willing to answer your questions.

Answer 2

There can be multiple ways to handle this situation. One that i would go with, is creating custom filters and annotating the methods or operations with a custom filter to update user's last access time.

public class UpdateLastAccessFilter : ActionFilterAttribute, IActionFilter
{
    void IActionFilter.OnActionExecuting(ActionExecutingContext filterContext)
    {
        // TODO: Add your action filter's tasks here

        // Log Action Filter call
        using (dbEntities context = new dbEntities())
        {

            var id = context.User.Claims.First(x => x.Type == "sub").Value;

        var user = db.AspNetUsers.Find(id);

        user.LastAccessed = DateTime.Now;

        await db.SaveChangesAsync();
            OnActionExecuting(filterContext);
        }
    }
}

and then decorate the methods or controllers for which you need to log access time.

[UpdateLastAccessFilter]
public class StoreController : Controller
{
    ...
}

More Details on custom filter

Answer 3

This may be because MyDbContext is disposable and needs to be wrapped in a using every time you need it.

Try this and see if it works:

using (var context = db)
{
    context.AspNetUsers.Find(id);
}

You may need to do the same with any subsequent use of db .

I'm assuming that MyDbContext has been registered to the IoC in the StartUp.cs ConfigureService(IServiceCollection services) function? Something like this:

services.AddDbContext<MyDbContext>(options =>
    options.UseSqlServer(Configuration.GetSection("ConnectionStrings:Sql").Value)
);