Why Does My Entity Framework Core Application Throw 'A second operation started on this context before a previous operation completed'?

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

When working with Entity Framework Core in an ASP.Net Core 2.0 project, you may encounter an error stating "A second operation started on this context before a previous operation completed." This error can occur even though the code runs without issues locally but fails when deployed to a staging server.

Possible Causes:

• Concurrency Issues: This error typically indicates that multiple operations are attempting to access the same context concurrently, which can lead to inconsistent results.
• Asynchronous Operations: Async/await operations can also trigger this error if async lambda expressions are being used.
• Dependency Injection: If the DbContext is resolved through native IoC or other IoC-Containers and is registered as scoped, it can cause problems in multithreaded environments.

Solution:

Register DbContext as Transient:

To resolve the concurrency issue caused by dependency injection, register the DbContext as transient instead of scoped. Use the following code:

services.AddTransient<MyContext>();

Avoid Async Lambda Expressions:

If asynchronous operations are being used, refactor the code to avoid using async lambda expressions.

Ensure Thread Safety:

Understand the limitations of the DbContext implementation and ensure thread safety by executing operations sequentially or using appropriate synchronization mechanisms.

Consider Other Factors:

• Check if any Hangfire jobs or other processes are accessing the same context concurrently.
• Review the code for any other potential concurrency issues.
• Check the database max length for the model that was modified.

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