Solving the Self-casting Include Challenge in Entity Framework Core 5/6

Discover how to adapt your Entity Framework Core queries in .NET 5/6 after the `Self-casting Include` trick breaks. Learn simple solutions and improve your coding skills!
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This video is based on the question https://stackoverflow.com/q/69969666/ asked by the user 'CarlJ' ( https://stackoverflow.com/u/363966/ ) and on the answer https://stackoverflow.com/a/69970055/ provided by the user 'Ivan Stoev' ( https://stackoverflow.com/u/5202563/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Self-casting Include Challenge in Entity Framework Core 5/6

If you're a developer working with Entity Framework Core, you might have come across a frustrating issue when upgrading from .NET Core 3.1 to .NET 5 or 6. In particular, the familiar and handy Self-casting Include trick you previously relied upon for managing complex queries no longer works. In this guide, we will explore the problem in detail and present a clear solution to get your queries up and running smoothly once again.

The Issue at Hand: What Happened?

In earlier versions of Entity Framework Core, you could create queries utilizing the IIncludableQueryable interface to include multiple navigation properties in a way that felt seamless. The trick involved returning an instance of IIncludableQueryable<Widget, Widget>, allowing you to easily include various properties without duplicating code. Here’s the method you might have written in EF Core 3.1:

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This approach worked well until you attempted to upgrade to .NET 5/6, where execution resulted in a runtime exception:

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This indicates that your specific return type is now unsupported due to changes in EF Core's architecture.

Understanding the Changes in Entity Framework Core

With the release of EF Core 5, new features were introduced, particularly around filtering Includes. One key takeaway from the updates is the realization that the original approach of using IIncludableQueryable<T, T> was limiting and unnecessary. The second generic type parameter is designed to facilitate chaining calls with ThenInclude, providing flexibility for nested property inclusion.

Key Concept

IIncludableQueryable T, P is meant for chaining deeper Includes, but using the same type for both makes it redundant. Instead, direct usage of IQueryable<T> gives you the flexibility to include other navigation properties while resetting the path as needed.

The Solution: Refactoring Your Queries

To resolve the issue while maintaining the method signature, you simply need to change the return type of your implementation to IQueryable<Widget>. This allows you to bypass the previous constraints while still achieving similar functionality.

New Implementation

Here’s how you can refactor the original method:

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From there, you can include additional navigation properties without hitting compilation errors:

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This setup not only resolves the issue but also enhances the clarity and maintainability of your code.

Conclusion

Upgrading to a new framework version can often bring unforeseen challenges, but understanding the core changes and adapting your techniques ensures a smoother transition. By refactoring your method to use IQueryable<Widget>, you can retain the powerful query capabilities of Entity Framework Core while avoiding the pitfalls introduced in .NET 5/6.

If you find yourself in a similar situation, tackle it head-on with thoughtful refactoring. By keeping your codebase adaptable, you can unlock new features and improvements while minimizing disruptions.

Feel free to experiment with your queries and don’t hesitate to reach out for more tips on mastering Entity Framework Core!

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