最基本的问题…
我有一个方法，它执行以下代码：

IList<Gig> gigs = GetGigs().WithArtist(artistId).ToList();

GetGigs（）方法通过LinqToSql从我的数据库中获取Gigs...
因此，当执行GetGigs（）.WithArtist（artistId）.ToList（）时，我会得到以下异常：

Member access 'ListenTo.Shared.DO.Artist Artist' of 'ListenTo.Shared.DO.Act' not legal on type 'System.Collections.Generic.List`1[ListenTo.Shared.DO.Act]

请注意，扩展函数“WithArtist”看起来像这样：

public static IQueryable<Gig> WithArtist(this IQueryable<Gig> qry, Guid artistId)
    {
        return from gig in qry
               where gig.Acts.Any(act => (null != act.Artist) && (act.Artist.ID == artistId))
               orderby gig.StartDate
               select gig;
    }

如果我将GetGigs（）方法替换为一个在code中构造gig集合的方法（而不是通过LinqToSQL从DB中），我不会得到异常。
所以我相当肯定问题出在我的LinqToSQl代码上，而不是对象结构。
然而，我不知道为什么LinqToSQL版本不工作，所以我把所有相关的代码都包括在下面。任何帮助都会非常感激！！
LinqToSQL代码....

public IQueryable<ListenTo.Shared.DO.Gig> GetGigs()
    {
        return from g in DBContext.Gigs
               let acts = GetActs(g.ID)
               join venue in DBContext.Venues on g.VenueID equals venue.ID
               select new ListenTo.Shared.DO.Gig
               {
                   ID = g.ID,
                   Name = g.Name,
                   Acts = new List<ListenTo.Shared.DO.Act>(acts),
                   Description  = g.Description,
                   StartDate    = g.Date,
                   EndDate      = g.EndDate,
                   IsDeleted    = g.IsDeleted,
                   Created      = g.Created,
                   TicketPrice  = g.TicketPrice,
                   Venue        =  new ListenTo.Shared.DO.Venue { 
                                    ID = venue.ID, 
                                    Name = venue.Name, 
                                    Address = venue.Address,
                                    Telephone = venue.Telephone,
                                    URL = venue.Website 
                   }

               };
    }


    IQueryable<ListenTo.Shared.DO.Act> GetActs()
    {
        return from a in DBContext.Acts

               join artist in DBContext.Artists on a.ArtistID equals artist.ID into art
               from artist in art.DefaultIfEmpty()

               select new ListenTo.Shared.DO.Act
               {
                    ID = a.ID,
                    Name = a.Name,
                    Artist = artist == null ? null : new Shared.DO.Artist
                    {
                       ID =  artist.ID,
                       Name = artist.Name
                    },
                    GigId = a.GigID

               };
    }

    IQueryable<ListenTo.Shared.DO.Act> GetActs(Guid gigId)
    {
        return GetActs().WithGigID(gigId);
    }

我已经包括了下面的Act，Artist和Gig对象的代码：

public class Gig : BaseDO
{

    #region Accessors

    public Venue Venue
    {
        get;
        set; 
    }

    public System.Nullable<DateTime> EndDate
    {
        get;
        set;
    }

    public DateTime StartDate
    {
        get;
        set;
    }

    public string Name
    {
        get;
        set;
    }

    public string Description
    {
        get;
        set;
    }

    public string TicketPrice
    {
        get;
        set;
    }

    /// <summary>
    /// The Act object does not exist outside the context of the Gig, therefore,
    /// the full act object is loaded here.
    /// </summary>
    public IList<Act> Acts
    {
        get;
        set;
    }

    #endregion
}

public class Act : BaseDO
{
    public Guid GigId { get; set; }
    public string Name { get; set; }
    public Artist Artist { get; set; }
}

public class Artist : BaseDO
{
    public string Name { get; set; }
    public string Profile { get; set; }
    public DateTime Formed { get; set; }
    public Style Style { get; set; }
    public Town Town { get; set; }
    public string OfficalWebsiteURL { get; set; }
    public string ProfileAddress { get; set; }
    public string Email { get; set; }
    public ImageMetaData ProfileImage { get; set; }

}

public class BaseDO: IDO
{
    #region Properties

    private Guid _id;

    #endregion

    #region IDO Members

    public Guid ID
    {
        get
        {
            return this._id;
        }
        set
        {
            this._id = value;
        }
    }



}

}