Custom Validation for nested model in .net core - asp.net-mvc

Question

I am trying to validate a nested model using custom validation. But the problem is AttributeAdapterBase.AddValidation function is never called on nested model. However it works well with simple class property
Custom required validation attribute:
public interface IId
{
long Id { get; set; }
}
public class Select2RequiredAttribute : RequiredAttribute
{
public Select2RequiredAttribute(string errorMessage = "") : base()
{
ErrorMessage = errorMessage;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
Type t = value.GetType();
if (typeof(IId).IsAssignableFrom(t))
{
if ((value as IId).Id == 0)
{
return new ValidationResult(ErrorMessage);
}
}
else
{
return new ValidationResult(ErrorMessage);
}
return ValidationResult.Success;
}
}
Attribute adapter base:
public class Select2RequiredAttributeAdapter : AttributeAdapterBase<Select2RequiredAttribute>
{
public Select2RequiredAttributeAdapter(Select2RequiredAttribute attribute, IStringLocalizer stringLocalizer) : base(attribute, stringLocalizer)
{
}
public override void AddValidation(ClientModelValidationContext context)
{
MergeAttribute(context.Attributes, "data-val", "true");
MergeAttribute(context.Attributes, "data-val-select2-required", GetErrorMessage(context));
}
public override string GetErrorMessage(ModelValidationContextBase validationContext)
{
return Attribute.ErrorMessage ?? GetErrorMessage(validationContext.ModelMetadata, validationContext.ModelMetadata.GetDisplayName());
}
}
Adapter provider:
public class Select2RequiredAdapterProvider : IValidationAttributeAdapterProvider
{
private readonly IValidationAttributeAdapterProvider _baseProvider = new ValidationAttributeAdapterProvider();
public IAttributeAdapter GetAttributeAdapter(ValidationAttribute attribute, IStringLocalizer stringLocalizer)
{
if (attribute is Select2RequiredAttribute)
{
return new Select2RequiredAttributeAdapter(attribute as Select2RequiredAttribute, stringLocalizer);
}
else
{
return _baseProvider.GetAttributeAdapter(attribute, stringLocalizer);
}
}
}
Startup.cs:
services.AddSingleton<IValidationAttributeAdapterProvider, Select2RequiredAdapterProvider>();
Model classes:
public interface IBaseBriefViewModel : IId
{
string Name { get; set; }
}
public class BaseBriefViewModel : IBaseBriefViewModel
{
public virtual long Id { get; set; }
public string Name { get; set; }
}
public class UserViewModel
{
public long Id { get; set; }
public string Name { get; set; }
[Select2Required("Branch is required.")]
public BaseBriefViewModel Branch { get; set; }
}
Branch select 2 partial view:
#model DataLibrary.ViewModels.BriefViewModels.BaseBriefViewModel
#{
var elementId = ViewData["ElementId"] != null && !string.IsNullOrEmpty(ViewData["ElementId"].ToString()) ? ViewData["ElementId"].ToString() : "branch-id";
}
<div class="form-group">
<label>Branch: <span class="text-danger"></span></label>
<div class="row">
<div class="#select2Class">
#Html.DropDownListFor(model => model.Id, new List<SelectListItem>() {
new SelectListItem()
{
Value = (Model!=null&&Model.Id>0)?Model.Id.ToString():"",
Text = (Model!=null&&Model.Id>0)?Model.Name:"",
Selected = (Model!=null&&Model.Id>0)?true:false,
}}, new { #id = elementId, #class = "form-control disable-field"})
#Html.ValidationMessageFor(model => model.Id, "", new { #class = "text-danger" })
</div>
</div>
</div>
<script>
$(function () {
var id = "#" + "#elementId";
var url = '/Branch/GetBranchsForSelect2';
var dataArray = function (params) {
params.page = params.page || 1;
return {
prefix: params.term,
pageSize: pageSize,
pageNumber: params.page,
};
};
Select2AutoCompleteAjax(id, url, dataArray, pageSize, "---Branch---");
});
</script>
All this code works well for server side. But for better user experience I want to show error before submitting form. How can I achieve this? I want to use this BaseBriefViewModel for a lot of Select2 in the project. So hard coding a static error message is not a good idea. What I really want to do is pass a error message from parent object. Like Branch is required in this specific case. Maybe in some other class I might pass Product is required
Any direction will be appreciated

Answer 1

At the moment this is not supported - but support is in planned. See dotnet github issue:
https://github.com/dotnet/runtime/issues/36093