Attribute.IsDefined doesn't see attributes applied with MetadataType class

Question

If I apply attributes to a partial class via the MetadataType attribute, those attributes are not found via Attribute.IsDefined(). Anyone know why, or what I'm doing wrong?

Below is a test project I created for this, but I'm really trying to apply custom attributes to a LINQ to SQL entity class - like this answer in this question.

Thanks!

using System;
using System.ComponentModel.DataAnnotations;
using System.Reflection;

namespace MetaDataTest
{
    class Program
    {
        static void Main(string[] args)
        {
            PropertyInfo[] properties = typeof(MyTestClass).GetProperties();

            foreach (PropertyInfo propertyInfo in properties)
            {
                Console.WriteLine(Attribute.IsDefined(propertyInfo, typeof(MyAttribute)));
                Console.WriteLine(propertyInfo.IsDefined(typeof(MyAttribute), true));
                Console.WriteLine(propertyInfo.GetCustomAttributes(true).Length);

                // Displays:
                // False
                // False
                // 0
            }

            Console.ReadLine();
        }
    }

    [MetadataType(typeof(MyMeta))]
    public partial class MyTestClass
    {
        public string MyField { get; set; }
    }

    public class MyMeta
    {
        [MyAttribute()]
        public string MyField { get; set; }
    }

    [AttributeUsage(AttributeTargets.All)]
    public class MyAttribute : System.Attribute
    {
    }
}

Answer 1

The MetadataType attribute is used to specify help specify the additional information on the data object. To access the additional attributes you would need to do something like the following:

using System;
using System.Linq;
using System.ComponentModel.DataAnnotations;
using System.Reflection;

namespace MetaDataTest
{
    class Program
    {
        static void Main(string[] args)
        {
      MetadataTypeAttribute[] metadataTypes = typeof(MyTestClass).GetCustomAttributes(typeof(MetadataTypeAttribute), true).OfType<MetadataTypeAttribute>().ToArray();
      MetadataTypeAttribute metadata = metadataTypes.FirstOrDefault();

   if (metadata != null)
   {
    PropertyInfo[] properties = metadata.MetadataClassType.GetProperties();

    foreach (PropertyInfo propertyInfo in properties)
    {
     Console.WriteLine(Attribute.IsDefined(propertyInfo, typeof(MyAttribute)));
     Console.WriteLine(propertyInfo.IsDefined(typeof(MyAttribute), true));
     Console.WriteLine(propertyInfo.GetCustomAttributes(true).Length);
     RequiredAttribute attrib = (RequiredAttribute)propertyInfo.GetCustomAttributes(typeof(RequiredAttribute), true)[0];
     Console.WriteLine(attrib.ErrorMessage);
    }

    // Results:
    // True
    // True
    // 2
    // MyField is Required
   }

            Console.ReadLine();
        }
    }

    [MetadataType(typeof(MyMeta))]
    public partial class MyTestClass
    {
        public string MyField { get; set; }
    }

    public class MyMeta
    {
        [MyAttribute()]
  [Required(ErrorMessage="MyField is Required")]
        public string MyField { get; set; }
    }

    [AttributeUsage(AttributeTargets.All)]
    public class MyAttribute : System.Attribute
    {
    }
}

This also includes a sample attribute to show how to extract info that was added.