How to Fix Entity Framework Core's 'A second operation started on this context before a previous operation completed' Error?

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

When working with Entity Framework Core within an ASP.Net Core 2.0 application, you may encounter an "InvalidOperationException" stating that a second operation started on the context before a previous operation completed.

Causes and Solutions:

The underlying cause of this error is that Entity Framework Core's context implementation is not thread-safe. To resolve this, ensure that you're registering your DbContext as Transient in your dependency injection configuration:

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

Alternatively, you can register the context directly as Transient:

services.AddTransient<MyContext>();

Avoid registering the context as Scoped:

services.AddDbContext<MyContext>();

Additional Considerations:

• Async/await operations may also trigger this error when using async lambda expressions.
• Using the context in multiple classes over multiple requests can cause issues as each class will get its own instance.

Understanding Transient Dependency:

Adding the context as transient means that each time the context is requested, a new instance is created. This prevents thread safety issues but also limits the ability to make changes to entities across multiple classes.

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