Entity Framework Core: A second operation started on this context before a previous operation completed

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I am not sure if you are using IoC and Dependency Injection to resolve your DbContext where ever it might be used. If you do and you are using native IoC from .NET Core (or any other IoC-Container) and you are getting this error, make sure to register your DbContext as Transient. Do

services.AddDbContext<MyContext>(ServiceLifetime.Transient);

OR

services.AddTransient<MyContext>();

instead of

services.AddDbContext<MyContext>();

AddDbContext adds the context as scoped, which might cause troubles when working with multiple threads.

Also async / await operations can cause this behaviour, when using async lambda expressions.

Adding it as transient also has its downsides. You will not be able to make changes to some entity over multiple classes that are using the context because each class will get its own instance of your DbContext.

The simple explanation for that is, that the DbContext implementation is not thread-safe. You can read more about this here

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