Bltoolkit将数据插入表

我有这个实体:

namespace Entities.dbo
{
    [TableName("tbl_snapshot")]
    public class Snapshot : AbstractEntity
    {
        [MapField("track")]
        public int TrackId { get; set; }
        [Association(CanBeNull = false, OtherKey = "id", ThisKey = "track")]
        public Track Track { get; set; }
        [MapField("snapshotnumber")]
        public int SnapshotNumber { get; set; }
        [MapField("data")]
        public string Data { get; set; }
}}

和我尝试插入一个新的快照到数据库，像这样:

public static void XXX(Snapshot snapshot)
        {
            using (var db = new MyDbManager())
            {
                var s = new Snapshot
                                 {
                                     Id = snapshot.Id,
                                     Data = snapshot.Data,
                                     SnapshotNumber = snapshot.SnapshotNumber,
                                     TrackId = snapshot.Track.Id
                                 };

                db.GetTable<Snapshot>().Insert(() => s);
            }
        }

你能看出有什么问题吗?我发送给XXX方法的快照看起来像这样:

(JSON序列化):

{"TrackId":2,"Track":null,"SnapshotNumber":2,"Data":"030405","Id":3}

你知道问题在哪里吗?

谢谢