Validate DateTime with FluentValidator

Question

This is my ViewModel class:

public class CreatePersonModel
{
    public string Name { get; set; }
    public DateTime DateBirth { get; set; }
    public string Email { get; set; }
}

CreatePerson.cshtml

@model ViewModels.CreatePersonModel
@{
    ViewBag.Title = "Create Person";
}

<h2>@ViewBag.Title</h2>

@using (Html.BeginForm())
{
    <fieldset>
        <legend>RegisterModel</legend>

        @Html.EditorForModel()

        <p>
            <input type="submit" value="Create" />
        </p>
    </fieldset>
}

CreatePersonValidator.cs

public class CreatePersonValidator : AbstractValidator<CreatePersonModel>
{
    public CreatePersonValidator()
    {
        RuleFor(p => p.Name)
            .NotEmpty().WithMessage("campo obrigatório")
            .Length(5, 30).WithMessage("mínimo de {0} e máximo de {1} caractéres", 5, 30)
            .Must((p, n) => n.Any(c => c == ' ')).WithMessage("deve conter nome e sobrenome");

        RuleFor(p => p.DateBirth)
            .NotEmpty().WithMessage("campo obrigatório")
            .LessThan(p => DateTime.Now).WithMessage("a data deve estar no passado");

        RuleFor(p => p.Email)
            .NotEmpty().WithMessage("campo obrigatório")
            .EmailAddress().WithMessage("email inválido")
            .OnAnyFailure(p => p.Email = "");
    }
}

When trying to create a person with an invalid date format:

Observations

As in my CreatePersonModel class the DateBirth property is a DateTime type, the asp.net MVC validation has done for me.

But I want to customize the error message using the FluentValidation.

I do not want to change the type of property for various reasons such as:

In a CreatePersonValidator.cs class, validation is to check if the date is in the past:

.LessThan (p => DateTime.Now)

Question

How to customize the error message without using DataAnnotations (using FluentValidator).

Answer 1

public CreatePersonValidator()
{
    RuleFor(courseOffering => courseOffering.StartDate)
       .Must(BeAValidDate).WithMessage("Start date is required");

    //....
}

private bool BeAValidDate(DateTime date)
{
    return !date.Equals(default(DateTime));
}

Answer 2

Have a look at the Fluent Validation documentation on GitHub:

https://github.com/JeremySkinner/FluentValidation/wiki

Try adding a RegEx Validator to ensure that the user's input (a string) can be parsed as a date correctly, prior to applying the Less Than Validator.

EDIT

Having run few test cases and looked at the source code for Fluent Validator I concede that the above approach won't work.

The standard error you get is added during the Model Binding phase, which happens before the fluent validation framework can access and check the model.

I assumed that the framework's authors had been clever and were injecting their validation code into the model binding phase. Looks like they aren't.

So the short answer is what you want to do does not appear to be possible.

Answer 3

As Stewart mentioned, it's not possible to use FluentValidation alone to get in front of the model binding in this way. I'd offer up two ideas/suggestions though:

1. If you really can't change the ViewModel type from DateTime to string, you could always clear the model state yourself after model binding and then run the validator manually (I'm assuming you've wired FluentValidation to execute automatically after model binding).
2. In scenarios like this, I would change the property to a string, but then use AutoMapper to map that into a DateTime for whatever business object / domain model / service contract request I need it to ultimately become. That way, you get the most flexibility with parsing and conversion on both sides of the model binding.

Answer 4

Try this one

RuleFor(f =>
        f.StartDate).Cascade(CascadeMode.StopOnFirstFailure).NotEmpty()
                    .Must(date => date != default(DateTime))
                    .WithMessage("Start date is required");

Answer 5

I got this to work with DateTime? using really simple code. If you use the built-in validator NotNull(), then you get client side validation, which has 2 benefits.

1. You don't have to worry about all the model binding stuff people are talking about in other answers. It's client side! ;)
2. The date the user entered does not get "wiped out". An invalid date will get set by to null by the Post, Model binding to null, Validation error, responding with the view now with a null value in the date. This happens fast, so the user does not see what is wrong with the date.

This is the code I used:

RuleFor(x => x.CompleteDate).NotNull().WithMessage("Complete Date is not a valid date.");

I tested it with a date of 11/31/2021 (There is no day 31 in November) and it worked great with client-side validation.

Win!