Fluent Validation in .NET Core

Fluent Validation is a popular library in the .NET ecosystem that provides a fluent interface for defining validation rules for your objects. It simplifies the process of validating complex models, ensuring your application data meets specified criteria before processing. In this article, we'll explore Fluent Validation in .NET Core 8, offering practical examples and best practices to help you leverage this powerful tool in your projects.

Fluent Validation is a .NET library for building strongly-typed validation rules. It offers a simple, fluent interface that allows developers to define validation logic for models in a clear and readable manner. This approach ensures your code is maintainable and less prone to errors compared to traditional validation techniques.

Setting Up Fluent Validation in .NET Core 8

To get started with Fluent Validation in .NET Core 8, you need to install the FluentValidation package. You can do this using the NuGet Package Manager or the .NET CLI.

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dotnet add package FluentValidation

After installing the package, you'll need to configure it in your project. Typically, this is done in the Startup.cs or Program.cs file:

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public class Startup

{

public void ConfigureServices(IServiceCollection services)

{

services.AddControllers();

services.AddFluentValidation(fv => fv.RegisterValidatorsFromAssemblyContaining<Startup>());

}

// Other configurations...

}

Creating a Validator

To create a validator, you need to define a class that inherits from AbstractValidator<T>, where T is the type of the model you want to validate. Here's an example of a simple validator for a User model:

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using FluentValidation;

public class User

{

public string FirstName { get; set; }

public string LastName { get; set; }

public string Email { get; set; }

public int Age { get; set; }

}

public class UserValidator : AbstractValidator<User>

{

public UserValidator()

{

RuleFor(user => user.FirstName).NotEmpty().WithMessage("First name is required.");

RuleFor(user => user.LastName).NotEmpty().WithMessage("Last name is required.");

RuleFor(user => user.Email).NotEmpty().EmailAddress().WithMessage("Valid email is required.");

RuleFor(user => user.Age).InclusiveBetween(18, 60).WithMessage("Age must be between 18 and 60.");