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Learn how to solve the `infinite` nested eager loading issue in Entity Framework Core with a simple configuration fix.
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How to Prevent Infinite Nested Eager Loading in EF Core

Entity Framework Core (EF Core) is a powerful ORM (Object-Relational Mapper) that can help streamline database operations in .NET applications. However, working with relationships between entities can sometimes lead to unexpected situations. One common issue developers face is the problem of infinite nested eager loading, especially in one-to-many relationships.

Understanding the Problem

In a typical scenario, you may have two entities that share a one-to-many relationship—let’s say Maps and MapNodes. When you attempt to eager load MapNodes along with Maps, you might notice that not only do you get the desired Map object with its associated MapNodes, but also each MapNode contains a reference back to the Map. This pattern can continue indefinitely, resulting in nested MapNodes again containing Map references, leading to an infinite loop in your data model.

Here’s a simplified view of the relationship:

Maps

Contains a collection of MapNodes

MapNodes

Contains a reference back to a Map

When querying this without proper limits, it can produce an extensive recursive structure, making it hard to manage or read.

The Solution

Fortunately, there’s a way to handle this situation and prevent such infinite loading. The trick lies in using the right settings for serialization in ASP.NET Core.

Step-by-Step Configuration

Add the Necessary NuGet Package

Since ASP.NET Core 3 replaced Microsoft.AspNetCore.Mvc.NewtonsoftJson with System.Text.Json, the new framework doesn’t support reference loop handling just yet. You will need to restore the old functionality by adding the Newtonsoft.Json package.

Run the following command in your Package Manager Console:

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Configure Reference Loop Handling

After adding the package, adjust your controller service configuration to utilize Newtonsoft.Json and set the Reference Loop Handling option. This tells the serializer to ignore references that would cause infinite loops.

Update your Startup.cs or wherever you configure services in your application:

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What This Configuration Does

By setting ReferenceLoopHandling to Ignore, EF Core will not include back references in the serialized output, effectively breaking the cycle that leads to infinite nesting. When you next execute your query to include MapNodes, your output will be neatly structured without the embattled back references:

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Conclusion

Handling one-to-many relationships efficiently in EF Core requires understanding how eager loading works and how serialization can affect your output. By following the steps above, you can effectively prevent infinite nested eager loading and ensure that your data remains user-friendly and manageable. If you're working with complex data models in EF Core, this configuration is an essential addition to your toolkit.

Feel free to reach out with questions or comments regarding this solution or any additional EF Core topics you'd like to explore further!