Fluent Validation is an open-source validation library for .NET that allows developers to define validation rules for their models in a fluent and easy-to-read manner. It supports both server-side and client-side validation, and can be used with ASP.NET Web Forms, MVC, Web API, and Core applications.
To implement Fluent Validation in a .NET application, follow these steps:
Install the Fluent Validation package using NuGet. You can install it using the Package Manager Console with the following command:
Install-Package FluentValidation
Create a validator class for your model. The validator class should inherit from the AbstractValidator class and override the Validate method to define the validation rules. For example, here's a validator class for a Person model:
public class PersonValidator : AbstractValidator<Person>
{
public PersonValidator()
{
RuleFor(p => p.FirstName).NotEmpty();
RuleFor(p => p.LastName).NotEmpty();
RuleFor(p => p.Email).EmailAddress();
RuleFor(p => p.Age).InclusiveBetween(18, 100);
}
}
In the above example, the PersonValidator class defines four validation rules for the Person model: the FirstName and LastName properties must not be empty, the Email property must be a valid email address, and the Age property must be between 18 and 100.
Use the validator class to validate your model. You can create an instance of the validator class and call its Validate method to validate your model. For example, here's how you can use the PersonValidator class to validate a Person object:
var person = new Person
{ FirstName = "John", LastName = "Doe", Email = "john.doe@example.com", Age = 25 };
var validator = new PersonValidator();
var result = validator.Validate(person);
if (result.IsValid)
{
// model is valid
}
else
{
// model is invalid, handle errors
foreach (var error in result.Errors)
{
Console.WriteLine($"{error.PropertyName}: {error.ErrorMessage}");
}
}
In the above example, we create a Person object with valid properties and then create an instance of the PersonValidator class. We then call the Validate method with the Person object, which returns a ValidationResult object. If the IsValid property of the ValidationResult object is true, the model is valid. Otherwise, we can loop through the Errors collection to handle the validation errors.
In summary, Fluent Validation is a validation library for .NET that allows you to define validation rules for your models in a fluent and easy-to-read manner. To implement it, you need to install the Fluent Validation package, create a validator class for your model, and use the validator class to validate your model.
