Validation in ASP.NET Core

We can use the default method of adding DataAnnotations attributes (like [Required]), build custom DataAnnotations or use FluentValidation package. For ASP.NET Core we need to install FluentValidation.AspNetCore.

FluentValidations

It’s a 3rd part validation library that is an alternative for the default DataAnnotations approach.

Some advantages:

• DataAnnotations is based on Attribute, so it doesn’t play well with the DI
• We can create validations that use multiple properties of an object (e.g. StartDate and EndDate)
• Easier to test
• Validation logic is outside of the models

Registration:

services.AddValidatorsFromAssemblyContaining<SomeDataValidator>();
services.AddFluentValidationAutoValidation(options => 
{ 
    options.DisableDataAnnotationsValidation = true;
});

Usage:

public class CommandValidator : AbstractValidator<Command>
{
    public CommandValidator()
    {
        RuleFor(n => n.Title)
            .NotEmpty()
            .WithMessge("Title cannot be empty");
    }
}