Dataannotations for list in blazor page - validation

Question

I use the following to do validations on a form in blazor(server)
<EditForm Model="#place" OnValidSubmit="HandleValidSubmit" Context="placesEdit" >
<DataAnnotationsValidator />
<InputText #bind-Value="place.Name"/>
<ValidationMessage For="() => place.Name" />
</EditForm>
#{place=new Place(); }
the property Name as a [required] - Attribute. This works fine. When submitting the form I see the error message and the HandleValidSubmit isn't called
But when I try to do the same with a List the validation isn't happening. No error is displayed and HandleValidSubmit is called instead even if the requirements are not met:
<EditForm Model="#places" OnValidSubmit="HandleValidSubmit" Context="placesEdit" >
<DataAnnotationsValidator />
#foreach(var place in places) {
<InputText #bind-Value="place.Name"/>
<ValidationMessage For="() => place.Name" />
}
</EditForm>
#{places=new List<Place>(); }
What has do be done that the Validator also works in the loop?

Answer 1

Try if this helps:
Add the Microsoft.AspNetCore.Components.DataAnnotations.Validation NuGet package.
This is a pre-release package and latest version is 3.2.0-rc1.20223.4. There is a plan to include this on the native Blazor SDK but that version should work up to .NET 5. https://github.com/dotnet/aspnetcore/issues/22238#issuecomment-634266426
Replace your DataAnnotationsValidator with ObjectGraphDataAnnotationsValidator
You can check if your issue gets resolved with Step 2. If not, continue to Step 3.
Annotate your list property with ValidateComplexType.
You will need to create a class that will contain your list property.
check the docs for more information: https://learn.microsoft.com/en-us/aspnet/core/blazor/forms-validation#nested-models-collection-types-and-complex-types
If you're using IValidatableObject like me, the above solution won't work. The workaround is to create another property to link the validation into.
e.g.
public class MyModel : IValidatableObject
{
public List<Place> Places { get; } = new List<Place>();
public object PlacesValidation { get; }
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
var isValid = ...;
if (isValid)
yield return new ValidationResult("Places is invalid.", new[] { nameof(PlacesValidation ) });
}
}
<ValidationMessage For="() => Model.PlacesValidation"/>