MapSettingAttribute.cs

using System;

[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
public class MapSettingAttribute : Attribute
{
    public string SettingKey
    {
        get { return _settingKey; }
    }

    string _settingKey = null;

    public MapSettingAttribute (string settingKey = null)
    {
        _settingKey = settingKey;
    }
}