aspnetcore/src/Microsoft.AspNet.Mvc.ModelBinding/Validation/RequiredAttributeAdapter.cs

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Microsoft.AspNet.Mvc.ModelBinding
{
    public class RequiredAttributeAdapter : DataAnnotationsModelValidator<RequiredAttribute>
    {
        public RequiredAttributeAdapter(RequiredAttribute attribute)
            : base(attribute)
        {
        }

        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
           [NotNull] ClientModelValidationContext context)
        {
            var errorMessage = GetErrorMessage(context.ModelMetadata);
            return new[] { new ModelClientValidationRequiredRule(errorMessage) };
        }
    }
}