How to use Fluent Validation with MudDatePicker

[masquinyo]

I have a MudDatePicker inside a MudForm using a Validator (Fluent Validation). The element has the For and the Validation attributes defined but when it is first time displayed is showing a Error in validation func: Object reference not set to an instance of an object. afterwards the picker validates the content as expected when there is no value given on form submission. Is the validator correctly defined? am I missing something? here are the code snippets:

MudDatePicker element:

<MudDatePicker Variant="Variant.Outlined"
                               Label="BirthDate"
                               MinDate="DateTime.Now.AddYears(-80)"
                               MaxDate="DateTime.Now"
                               @bind-Date="_employeeContact.BirthDate"
                               Editable="true"
                               DisableToolbar="false"
                               Class="mt-0"
                               For="@(() => _employeeContact.BirthDate)"
                               Validation="@(_employeeValidator.ValidateValue)"
                               @ref="_picker" />

Object:

public class EmployeeContact
    {
        public string Name { get; set; } = default!;
        public string LastName { get; set; } = default!;
        public Department Department { get; set; } = default!;
        public DateTime? BirthDate { get; set; } = new DateTime();
    }

Validator:

public class EmployeeValidator : AbstractValidator<EmployeeContact>
    {
        public EmployeeValidator()
        {
            RuleFor(x => x.Name)
            .NotEmpty()
            .MinimumLength(1);

            RuleFor(x => x.LastName)
            .NotEmpty()
            .MinimumLength(2);

            RuleFor(x => x.Department)
            .NotNull();

            RuleFor(x => x.BirthDate)
            .NotNull();
        }

        public Func<object, string, Task<IEnumerable<string>>> ValidateValue => async (model, propertyName) =>
        {
            var result = await ValidateAsync(ValidationContext<EmployeeContact>.CreateWithOptions((EmployeeContact)model, x => x.IncludeProperties(propertyName)));
            if (result.IsValid)
                return Array.Empty<string>();
            return result.Errors.Select(e => e.ErrorMessage);
        };
    }

Rendered for the first time:

Form validation triggered on Form Submit with contents cleared (expected):

[masquinyo]

Update: I have changed the MudForm element to be an EditForm instead, also replaced the FluentValidaton with DataAnnotationsValidator now everything is behaving as expected.

[Noggington]

Hi - Did you ever get to the bottom of this? I am having exactly the same problem. But only with the MudDatePicker - the other MudControls work fine - just the MudDatePicker.

[Noggington]

I ended up dumping FluentValidation and used component DataAnnotations validation as well via edit form.

[glondono]

Same problem here, but I do require fluent validation because in my case, the same model can be validated in multiple ways depending on the context of the app. Does anyone have any ideas?

[Yomodo]

Same problem here, but I do require fluent validation because in my case, the same model can be validated in multiple ways depending on the context of the app. Does anyone have any ideas?

Perhaps Value Object can help?

[Noggington]

I originally used Value - but that didn't hold the selected date value correctly so changed to Date property. The docs specify to use the Date property as well for two way binding which is what I needed.

I am using DateTime values for these fields.

[tmfsmurphy]

I'm having the same issue using FluentValidation with MudDatePicker. Just like @glondono I cannot switch to DataAnnotations validation because I need to reuse my forms and validators elsewhere.

[chazkiker2]

I submitted an issue for this: #3876

Please refer to this snippet for an example of the issue