Handling Unhandled Exceptions in .NET: Resolving Schema ID Conflicts with Swashbuckle.AspNetCore.Swagger

When working with Swashbuckle.AspNetCore.Swagger for API documentation in .NET, you might encounter a peculiar error regarding schema IDs. This error often appears as follows:

Can't use schemaId "$Module" for type "$System.Reflection.Module". The same schemaId is already used for type "$Prjct.Data.Models.Module"

This error indicates a conflict between schema IDs, specifically when two different types are trying to use the same ID. In this case, it clashes between System.Reflection.Module and Prjct.Data.Models.Module. This blog post will explain why this error occurs and how to resolve it.

Understanding the Error

The Swashbuckle library uses schema IDs to generate unique identifiers for each model in your API documentation. By default, it generates these IDs based on the class names. If two different classes share the same name but reside in different namespaces, Swashbuckle might generate the same schema ID for both, leading to a conflict.

In the error message:

Can't use schemaId "$Module" for type "$System.Reflection.Module". The same schemaId is already used for type "$SAM.Data.Models.Module"

The conflict arises because both System.Reflection.Module and SAM.Data.Models.Module are being assigned the same schema ID $Module.

Causes and Solutions

Cause: Conflicting Class Names

The primary cause is having multiple classes with the same name in different namespaces. Swashbuckle doesn’t differentiate between namespaces when generating schema IDs by default.

Solution 1: Rename the Class

One straightforward solution is to rename one of the conflicting classes. This approach avoids the conflict altogether by ensuring unique class names across your project. However, renaming classes might not always be feasible, especially in large projects or when dealing with third-party libraries.

Solution 2: Customize Schema IDs

A more flexible solution involves customizing how Swashbuckle generates schema IDs. By providing a custom schema ID generation logic, you can ensure unique IDs for each type, even if they share the same name. This approach can be implemented in your Startup.cs file:

public void ConfigureServices(IServiceCollection services)
{
    services.AddSwaggerGen(options =>
    {
        options.CustomSchemaIds(type => type.ToString());
    });
}

In the above code snippet, the CustomSchemaIds method is used to generate schema IDs based on the full type name (including the namespace). This ensures that each schema ID is unique, resolving the conflict.

Conclusion

Schema ID conflicts in Swashbuckle.AspNetCore.Swagger can be frustrating, but they are relatively easy to resolve. By either renaming your classes or customizing the schema ID generation, you can ensure that your API documentation is generated without errors.

Remember, when customizing schema IDs, it’s essential to choose a method that guarantees uniqueness, such as using the full type name. This approach not only resolves the conflict but also maintains clarity in your API documentation.

By understanding the root cause of schema ID conflicts and implementing these solutions, you can enhance the reliability and maintainability of your .NET applications, ensuring smooth integration with Swashbuckle for API documentation.

Feel free to share your thoughts or any additional tips in the comments below. Happy coding!