gistfile1.cs

[CatalogContentType(GUID = "64ED6E28-07B1-4F18-A075-046D1557EFFE")]
public class Product : ProductContent, IResourceable
{
    public virtual string ContentAssetIdInternal { get; set; }

    public Guid ContentAssetsID
    {
        get
        {
            Guid assetId;
            if (Guid.TryParse(ContentAssetIdInternal, out assetId))
                return assetId;
            return Guid.Empty;
        }
        set
        {
            ContentAssetIdInternal = value.ToString();
            this.ThrowIfReadOnly();
            IsModified = true;
        }
    }
}