FluentValidation in ASP.NET Core: Why One Validator per Request Is the Real Best Practice

The text discusses the importance of robust validation in .NET Web APIs, emphasizing its role in protecting systems from bad data. FluentValidation is presented as the preferred solution, offering a fluent, strongly-typed approach to validation instead of using attributes. This approach promotes cleaner API models and a dedicated validation layer. The article contrasts the use of FluentValidation with the drawbacks of embedding validation logic directly in controllers, highlighting issues like duplication and increased complexity. It then illustrates how to implement FluentValidation in ASP.NET Core, including package installation, creating request DTOs, defining validators, and registering them within the application. The text strongly discourages the use of generic validators, explaining why they lead to code complexity and a loss of type safety. It advocates for the standard practice of creating one validator per request, aligning with each API contract for better organization. The article also touches on how to reuse validation logic effectively using rule extensions to maintain clean and reusable validators. Ultimately, the text promotes FluentValidation as a design choice, leading to safer, cleaner, and more maintainable APIs, which are characteristics of production-grade .NET systems.