ANTOOZA-BACKEND/SharedKernel/Extensions/ModelStateDictionaryExtensions.cs

using Microsoft.AspNetCore.Mvc.ModelBinding;

namespace SharedKernel.Extensions;

public static class ModelStateDictionaryExtensions
{
    public static string GetErrorMessages(this ModelStateDictionary modelState, string separator = "\n")
    {
        var errors = modelState
            .Where(kvp => kvp.Value?.Errors.Count > 0)
            .SelectMany(kvp => kvp.Value!.Errors)
            .Select(e => string.IsNullOrWhiteSpace(e.ErrorMessage) ? "Invalid value." : e.ErrorMessage)
            .ToArray();

        return string.Join(separator, errors);
    }
}