Umbraco-CMS/src/Umbraco.Web.Common/Extensions/ModelStateExtensions.cs

using System.Collections.Generic;
using System.Linq;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ModelBinding;

namespace Umbraco.Extensions
{
    public static class ModelStateExtensions
    {
        /// <summary>
        /// Checks if there are any model errors on any fields containing the prefix
        /// </summary>
        /// <param name="state"></param>
        /// <param name="prefix"></param>
        /// <returns></returns>
        public static bool IsValid(this ModelStateDictionary state, string prefix) =>
            state.Where(v => v.Key.StartsWith(prefix + ".")).All(v => !v.Value?.Errors.Any() ?? false);

        public static IDictionary<string, object> ToErrorDictionary(this ModelStateDictionary modelState)
        {
            var modelStateError = new Dictionary<string, object>();
            foreach (KeyValuePair<string, ModelStateEntry> keyModelStatePair in modelState)
            {
                var key = keyModelStatePair.Key;
                ModelErrorCollection errors = keyModelStatePair.Value.Errors;
                if (errors != null && errors.Count > 0)
                {
                    modelStateError.Add(key, errors.Select(error => error.ErrorMessage));
                }
            }
            return modelStateError;
        }

        /// <summary>
        /// Serializes the ModelState to JSON for JavaScript to interrogate the errors
        /// </summary>
        /// <param name="state"></param>
        /// <returns></returns>
        public static JsonResult? ToJsonErrors(this ModelStateDictionary state) =>
            new JsonResult(new
            {
                success = state.IsValid.ToString().ToLower(),
                failureType = "ValidationError",
                validationErrors = from e in state
                                   where e.Value.Errors.Count > 0
                                   select new
                                   {
                                       name = e.Key,
                                       errors = e.Value.Errors.Select(x => x.ErrorMessage)
                                           .Concat(
                                               e.Value.Errors.Where(x => x.Exception != null).Select(x => x.Exception!.Message))
                                   }
            });
    }
}