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");
    }
}

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