ANTOOZA-BACKEND/SharedKernel/Attributes/MaxFileCountAttribute.cs

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

namespace SharedKernel.Attributes;

/*
 * 파일 개수 제한
 */
[AttributeUsage(AttributeTargets.Property)]
public class MaxFileCountAttribute : ValidationAttribute
{
    private readonly int _maxCount;
    public MaxFileCountAttribute(int maxCount)
    {
        _maxCount = maxCount;
    }

    public override bool IsValid(object? value)
    {
        if (value is IEnumerable files)
        {
            return files.Cast<object>().Count() <= _maxCount;
        }

        return true;
    }

    public override string FormatErrorMessage(string name)
    {
        var template = string.IsNullOrWhiteSpace(ErrorMessage) ? "{0}은(는) 최대 {1}개까지 등록 가능합니다." : ErrorMessage;

        return string.Format(template, name, _maxCount);
    }
}