Building a 3-Tier App with Silverlight 3, .NET RIA Services, and Azure Table Storage

// AzureContext.cs
//

using System;
using System.ComponentModel;
using System.Runtime.Serialization;
using Microsoft.Azure.Linq;
using System.ComponentModel.DataAnnotations;

namespace Microsoft.Azure.DomainServices {

    public sealed class AzureTypeDescriptionProvider : TypeDescriptionProvider {

		public AzureTypeDescriptionProvider()
			: base()
		{
		}

		public AzureTypeDescriptionProvider(TypeDescriptionProvider parentProvider)
			: base(parentProvider)
		{
		}
		
		public AzureTypeDescriptionProvider(TypeDescriptionProvider parentProvider, Type domainServiceType, bool isDesignTime)
            : base(parentProvider) {
        }

        public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance) {
            ICustomTypeDescriptor baseTypeDescriptor = base.GetTypeDescriptor(objectType, instance);
            if (typeof(Entity).IsAssignableFrom(objectType) == false) {
                return baseTypeDescriptor;
            }

            return new AzureTypeDescriptor(objectType, baseTypeDescriptor);
        }


        private sealed class AzureTypeDescriptor : CustomTypeDescriptor {

            private Type _entityType;

            public AzureTypeDescriptor(Type entityType, ICustomTypeDescriptor parentTypeDescriptor)
                : base(parentTypeDescriptor) {
                _entityType = entityType;
            }

            public override PropertyDescriptorCollection GetProperties() {
                PropertyDescriptorCollection propDescs = base.GetProperties();

                PropertyDescriptor[] newPropDescs = new PropertyDescriptor[propDescs.Count + 1];
                propDescs.CopyTo(newPropDescs, 0);

                newPropDescs[newPropDescs.Length - 1] = new ETagPropertyDescriptor(_entityType);

                return new PropertyDescriptorCollection(newPropDescs);
            }
        }


        private sealed class ETagPropertyDescriptor : PropertyDescriptor {

            private Type _entityType;

            public ETagPropertyDescriptor(Type entityType)
                : base("_ETag", new Attribute[] {
                                    // new ReadOnlyAttribute(true),
                                    new BindableAttribute(false),
                                    new DataMemberAttribute(),
									new DisplayAttribute() { AutoGenerateField = false }
                                }) {
                _entityType = entityType;
            }

            public override Type ComponentType {
                get {
                    return _entityType;
                }
            }


            public override bool IsReadOnly {
                get {
                    // TODO: Hack to make the GetValue hack which returns random values
                    //       on each call work as expected.
                    // return true;
                    return false;
                }
            }

            public override Type PropertyType {
                get {
                    return typeof(string);
                }
            }

            public override bool SupportsChangeEvents {
                get {
                    return false;
                }
            }

            public override void AddValueChanged(object component, EventHandler handler) {
            }

            public override bool CanResetValue(object component) {
                return false;
            }

            public override object GetValue(object component) {
                // TODO: How do we get to the parent domain service
                // TODO: Hack to make the entity appear as if it changed during an update.
                return Guid.NewGuid().ToString();
                // return null;
            }

            public override void RemoveValueChanged(object component, EventHandler handler) {
            }

            public override void ResetValue(object component) {
                throw new NotSupportedException();
            }

            public override void SetValue(object component, object value) {
                // TODO: How do we get to the parent domain service
            }

            public override bool ShouldSerializeValue(object component) {
                return true;
            }
        }
    }
}