FluentValidation: Check if one of two fields are empty

Question

I have this model

public class Person
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }  
}

I want to create a validation where either FirstName or LastName must be filled in by user. I installed FluentValidation and created a customvalidator class

public class PersonValidator:AbstractValidator<Person>
{
    public PersonValidator()
    {
        RuleFor((person=>person.FirstName)//don't know how to check if one is empty
    }
}

To check just one field I could just do RuleFor(person => person.FirstName).NotNull();

But how do I check if one of them is null.

Also, is it possible, once validation is created via fluentValidation, use it on the client side to show error?

Edit1

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);
        FluentValidationModelValidatorProvider.Configure();
    }
//creating validation
namespace WebApplication1.Models.CustomValidator
{
    public class PersonValidator:AbstractValidator<Person>
    {
        public PersonValidator()
        {
            RuleFor(m => m.FirstName).NotEmpty().When(m => string.IsNullOrEmpty(m.LastName)).WithMessage("*Either First Name or Last Name is required");
            RuleFor(m => m.LastName).NotEmpty().When(m => string.IsNullOrEmpty(m.FirstName)).WithMessage("*Either First Name or Last Name is required");
        }
    }

}
//model class
[Validator(typeof(PersonValidator))]
public class Person
{
    public Person()
    {
        InterestList = new List<string>();
    }
    public int Id { get; set; }
    public int ContactId { get; set; }
    [RequiredIfEmpty("LastName")]
    public string FirstName { get; set; }
    [RequiredIfEmpty("FirstName")]
    public string LastName { get; set; }
    public string EmailAddress { get; set; }
    public string Phone { get; set; }
    public string Country { get; set; }
    public List<string> InterestList { get; set; } 
}
//view
@model WebApplication1.Models.Person

<script src="@Url.Content("~/Scripts/jquery-1.8.2.min.js")"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.min.js")"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")"></script>
<script src="@Url.Content("~/Scripts/jquery.unobtrusive-ajax.min.js")" type="text/javascript"></script>

@Html.ValidationSummary(true)
@using(Html.BeginForm("AddPerson","Person",FormMethod.Post))
{
    <div class="label">First Name</div>
    <div class="input-block-level">@Html.TextBoxFor(m=>m.FirstName)@Html.ValidationMessageFor(m=>m.FirstName)</div>
    <br/>
    <div class="label">Last Name</div>
    <div class="input-block-level">@Html.TextBoxFor(m=>m.LastName)@Html.ValidationMessageFor(m=>m.LastName)</div>
    <button type="submit" class="btn-primary">Submit</button>
}

What is the `RequiredIfEmpty` attribute? – Zabavsky Jan 14 '14 at 15:45 — Zabavsky, Jan 14 '14 at 15:45

score 127 · Accepted Answer · edited Nov 13 '18 at 11:44

127

You can use When/Unless condition:

RuleFor(m => m.FirstName).NotEmpty().When(m => string.IsNullOrEmpty(m.LastName));
RuleFor(m => m.LastName).NotEmpty().When(m => string.IsNullOrEmpty(m.FirstName));

or

RuleFor(m => m.FirstName).NotEmpty().Unless(m => !string.IsNullOrEmpty(m.LastName));
RuleFor(m => m.LastName).NotEmpty().Unless(m => !string.IsNullOrEmpty(m.FirstName));

As for your second question, FluentValidation works with client-side validation, but not all rules are supported. Here you can find validators, that are supported on the client-side:

NotNull/NotEmpty
Matches (regex)
InclusiveBetween (range)
CreditCard
Email
EqualTo (cross-property equality comparison)
Length

For rules that are not in the list you have to write your own FluentValidationPropertyValidator and implement GetClientValidationRules. You can find a few samples of this on the StackOverflow by doing simple search.

edited Nov 13 '18 at 11:44

LeftyX

35,328
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answered Jan 14 '14 at 14:16

Zabavsky

13,340
8
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I'm using `.NotEmpty` and `.When` so to show client side error what shoud i do? I'll edit my question so you can see what new i have added. – Cybercop Jan 14 '14 at 14:58
I just realized it doesn't work for when and unless. But still the fluentValidation is not working – Cybercop Jan 14 '14 at 15:20
1

Is there any way to do this but without having to populate both properties with the model state error? – Ciaran Gallagher Jul 25 '18 at 12:43
1

not working for me, it is still complaining one field is missing while the other is populated – phil123456 Mar 23 '21 at 07:36

score 21 · Answer 2 · answered Sep 04 '14 at 14:07

21

Try this

RuleFor(person => person).Must(person => !string.IsNullOrEmpty(person.FirstName) || !string.IsNullOrEmpty(person.LastName))

answered Sep 04 '14 at 14:07

Fat Shogun

987
1
10
18

This fails when using ValidateAsync :( – Purusartha Nov 06 '15 at 00:11
This doesn't work for me. I got the following error: Property name could not be automatically determined for expression item => item. Please specify either a custom property name by calling 'WithName'. – Vlad Schnakovszki Dec 04 '15 at 11:05
@VladSchnakovszki what's item? – Fat Shogun Dec 04 '15 at 12:37
@FatShogun, it's the equivalent of person in your example. – Vlad Schnakovszki Dec 04 '15 at 14:11
@VladSchnakovszki afaik that error is produced when trying to validate something other than a property. Paste your relevant code and I'll see if I can provide you with a better answer. – Fat Shogun Dec 04 '15 at 14:18

score 6 · Answer 3 · answered Feb 06 '16 at 12:17

I did like this to check charges entered are same to previous one or not. If charges are same as previous one than it'll give an error. This worked for me.

public class CasualMealChargeValidator : AbstractValidator<CasualMealCharge>
{
    public CasualMealChargeValidator(CasualMealCharge CMC)
    {
        //RuleFor(x => x.BankName).NotEmpty().When(pm => pm.PaymentMode == "Cheque").WithMessage("Enter Bank.");
        RuleFor(x => x).Must(x => x.DN != CMC.DN || x.BF != CMC.BF || x.LN != CMC.LN).WithMessage("Not Saved - Meal charges are same as current charges.").WithName("CMFor");
    }
}

score 5 · Answer 4 · answered Jul 05 '18 at 23:53

5

Finally, this worked for me. I wanted to validate three properties where at least one is required. It returns an error message only once.

RuleFor(p => p).Cascade(CascadeMode.StopOnFirstFailure)
            .Must(p => !string.IsNullOrWhiteSpace(p.FirstName))
            .When(p => p.Id == 0 && string.IsNullOrWhiteSpace(p.LastName)).WithMessage("At least one is required (Id, FirstName, LastName).")
            .Must(p => !string.IsNullOrWhiteSpace(p.LastName))
            .When(p => p.Id == 0 && string.IsNullOrWhiteSpace(p.FirstName)).WithMessage("At least one is required (Id, FirstName, LastName).")
            .Must(p => p.Id != 0)
            .When(p => string.IsNullOrWhiteSpace(p.FirstName) && string.IsNullOrWhiteSpace(p.LastName)).WithMessage("At least one is required (Id, FirstName, LastName).");

answered Jul 05 '18 at 23:53

Nishith Shah

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Surely you only need the first Must()/When()? – sixeyes Oct 02 '19 at 12:19
@sixeyes Are you asking or saying that I can improve? – Nishith Shah Oct 04 '19 at 00:01
Perhaps I'm missing something, but if all three values are null / 0, the first Must() would trigger. Why bother with the other two Must(). If you we're having different messages as @dummyDev answer it would make sense but your messages are all the same. I copied your code as it was what I was after but once I'd written my tests I found I didn't need the other Must(), hence my comment. – sixeyes Oct 07 '19 at 14:37

Carsten Heine · Answer 5 · 2014-01-14T14:34:09.863

2

I don't know that library, but if you just want to check those two properties for null, then you can use this:

RuleFor(person => person.FirstName ?? person.LastName).NotNull();

EDIT This doesn't work, because it throws an InvalidOperationException. Use Zabavsky's solution instead.

edited Jan 14 '14 at 14:34

answered Jan 14 '14 at 14:00

Carsten Heine

144
5

2

And here the OP really wants to use `NotEmpty()` as that checks for both `null` or and empty string. – Mike Perrenoud Jan 14 '14 at 14:03
1

The OP clearly say he's using `FluentValidation`. I don't know if I have outdated library, but this answer threw `System.InvalidOperationException` with error message: Property name could not be automatically determined for expression person => (person.FirstName ?? person.LastName). Please specify either a custom property name by calling 'WithName'. – IronGeek Jan 14 '14 at 14:21
@IronGeek You are right. I edited the answer. Use Zabavsky's solution instead. – Carsten Heine Jan 14 '14 at 14:35

dummyDev · Answer 6 · 2018-11-26T16:00:49.597

A nice rule-set to check if one of two fields are empty, as well as coming up with meaningful error codes is the following:

public CustomerSourceValidator()
    {
        CascadeMode = CascadeMode.StopOnFirstFailure;

        RuleFor(x => x)
            .NotNull().WithErrorCode("source_id_or_email_required")
            .When(source => source.Email == null && source.Id == null);

        RuleFor(x => x.Id)
            .NotNull().WithErrorCode("source_id_required")
            .Matches(CommonValidationRegex.CustomerIdRegexString).WithErrorCode("source_id_invalid")
            .When(source => source.Id != null);

        RuleFor(x => x.Email)
            .NotNull().WithErrorCode("source_email_required")
            .Matches(CommonValidationRegex.EmailRegexString).WithErrorCode("source_email_invalid")
            .When(source => source.Email != null);
    }

FluentValidation: Check if one of two fields are empty

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