Resolving Fluent Validator Issues in Class Libraries for ASP.NET Core Projects

Encountering problems with `Fluent Validation` when using class libraries in `ASP.NET Core`? Discover the solutions to ensure client-side validation works seamlessly in your projects.
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Troubleshooting Fluent Validation in ASP.NET Core Class Libraries

If you've ever faced issues with Fluent Validation while working on your ASP.NET Core projects, you're not alone. Many developers experience a hiccup when integrating validation from a class library. Specifically, the client-side validation works flawlessly when implemented directly within the ASP.NET Core project, but fails to execute when the validators are housed in a class library.

In this post, we'll explore the underlying problem and the straightforward solution to ensure your Fluent Validator functions correctly, allowing you to achieve effective validation in your applications.

Understanding the Problem

When you create a class library to manage your validation logic, you may find that client-side validation does not function as expected. For instance, consider the following implementation of a Person model and its corresponding validator:

[[See Video to Reveal this Text or Code Snippet]]

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While this setup appears correct, clients may report issues with client-side validation when the validators are defined in a class library due to the nullable reference types setting in the project.

The Solution: Steps to Fix the Issue

Upon investigation, it becomes clear that the nullable references setting in your class library can inhibit the functionality of client-side validation in ASP.NET Core. Here’s how to address this issue:

Step 1: Adjust the Project File

You need to remove the nullable setting in your *.csproj file. Specifically, locate the line that defines nullable references and delete it:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Define Nullable Properties Explicitly

After adjusting the project file, redefine your properties to handle nullability explicitly. For example, update your model property as follows:

[[See Video to Reveal this Text or Code Snippet]]

By defining your properties as nullable, you can leverage the ability of Fluent Validation to manage potential null values effectively.

Conclusion

Implementing validation in class libraries for ASP.NET Core requires careful attention to project configurations, particularly concerning nullable reference types. By removing the nullable setting from your project file and explicitly defining your properties, you can ensure that Fluent Validation works seamlessly both on the server and client sides.

As always, testing your validation implementation thoroughly after making these adjustments is crucial for ensuring the robustness of your application. Happy coding!