FluentValidation vs Data Annotations: Which is Better?

What are the main differences between FluentValidation and Data Annotations?

FluentValidation is a library for building strongly-typed validation rules, while Data Annotations are attributes used for validation in .NET. FluentValidation offers more flexibility and a fluent interface, whereas Data Annotations are simpler and built into the framework.

Can you give me an example of how to use FluentValidation?

Sure! Here's a simple example:

public class User {
    public string Name { get; set; }
    public int Age { get; set; }
}

public class UserValidator : AbstractValidator<User> {
    public UserValidator() {
        RuleFor(user => user.Name).NotEmpty();
        RuleFor(user => user.Age).InclusiveBetween(18, 60);
    }
}

This defines a User class and a UserValidator that checks if the name is not empty and the age is between 18 and 60.

What are the advantages of using FluentValidation over Data Annotations?

FluentValidation provides a more expressive syntax, better separation of concerns, and the ability to create complex validation rules. It also allows for conditional validation and custom error messages, which can be more challenging with Data Annotations.

Are there any performance differences between the two?

In general, the performance difference is negligible for most applications. However, FluentValidation can be more efficient in scenarios with complex validation logic due to its optimized rule evaluation.