Fluent NHibernate复合ID表问题

我有点不熟悉休眠，我遇到了一个问题。我有以下表格:

表1: 表名: Users，列1: ID，列2: Name

表2: 表名: 列1: ID，第二列:描述

表3: 表名: usertodomisations，列1: UserID，列2: MissionID，列3:排名

代码如下:MissionMap:

public class MissionMap : ClassMap<Mission>
{
    public const string TableName = "tblMissions";
    public const string c_id = "achID";
    public const string c_name = "achName";
    public MissionMap()
    {
        Table(TableName);
        Id(x => x.ID).Column(c_id).Not.Nullable();
        Map(x => x.Name).Column(c_name).Not.Nullable();
        HasMany(x => x.UserToDoList).Cascade.All().Inverse().KeyColumn(UserToDoMap.c_missionID);
    }
}

用户地图:

public class UserMap : ClassMap<User>
{
    public const string TableName = "tblUsers";
    public const string c_id = "usrID";
    public const string c_userName = "usrUserName";
    public UserMap()
    {
        Table(TableName);
        Id(x => x.ID).Column(c_id).Not.Nullable();
        Map(x => x.UserName).Column(c_userName).UniqueKey(DBConsts.UniqueKeys.User_UserName).Not.Nullable();
        HasMany(x => x.UserToDoList).Cascade.All().Inverse().KeyColumn(UserToDoMap.c_userID);
    }
}

UserToDo地图:

public class UserToDoMap : ClassMap<UserToDo>
{
    public const string TableName = "tblToDoList";
    public const string c_userID = "tdlUserID";
    public const string c_missionID = "tdlMissionID";
    public const string c_rank = "tdlRank";
    public UserToDoMap()
    {
        Table(TableName);
        CompositeId().KeyReference(x => x.User, c_userID).KeyReference(x => x.Achievment, c_missionID);
        References(x => x.User).Column(c_userID).Cascade.All().UniqueKey(DBConsts.UniqueKeys.ToDoList_UserRanks).Not.Nullable();
        References(x => x.Mission).Column(c_missionID).Cascade.All().Not.Nullable();
        Map(x => x.Rank).Column(c_rank).UniqueKey(DBConsts.UniqueKeys.ToDoList_UserRanks).Not.Nullable();
    }
}

我的问题是我不能保存新行。我可以选择并获取所有的东西，但不能保存。什么好主意吗?

谢谢。

编辑:我什么也得不到。不会抛出异常，但不会将行添加到DB中。顺便说一句，我在UserToDo对象上使用save方法。

编辑2:在docmanhattan回答之后，这里是代码:

UserToDoMap:

public class UserToDoMap : ClassMap<UserToDo>
{
    public const string TableName = "tblToDoList";
    public const string c_userID = "tdlUserID";
    public const string c_missionID = "tdlMissionID";
    public const string c_rank = "tdlRank";
    public UserToDoMap()
    {
        Table(TableName);
        CompositeId<UserToDoId>(x => x.ID)
            .KeyReference(x => x.UserIdPart, c_userID)
            .KeyReference(x => x.MissionIdPart, c_missionID);
        References(x => x.ID.UserIdPart).Column(c_userID).Cascade.All().UniqueKey(DBConsts.UniqueKeys.ToDoList_UserRanks).Not.Nullable();
        References(x => x.ID.MissionIdPart).Column(c_missionID).Cascade.All().Not.Nullable();
        Map(x => x.Rank).Column(c_rank).UniqueKey(DBConsts.UniqueKeys.ToDoList_UserRanks).Not.Nullable();
    }
}

UserToDoId实体:

public class UserToDoId
{
    public virtual User UserIdPart { get; set; }
    public virtual Mission MissionIdPart { get; set; }
    public override bool Equals(object obj)
    {
        UserToDoId recievedObject = (UserToDoId)obj;
        if ((UserIdPart.ID == recievedObject.UserIdPart.ID) &&
            (MissionIdPart.ID == recievedObject.MissionIdPart.ID))
        {
            return (true);
        }
        return (false);
    }
    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
}

UserToDo实体:

public class UserToDo
{
    public virtual UserToDoId ID { get; set; }
    public virtual int Rank { get; set; }
    public UserToDo()
    {
    }
    public override bool Equals(object obj)
    {
        UserToDo recievedObject = (UserToDo)obj;
        if ((ID.UserIdPart.ID == recievedObject.ID.UserIdPart.ID) &&
            (ID.MissionIdPart.ID == recievedObject.ID.MissionIdPart.ID) &&
            (Rank == recievedObject.Rank))
        {
            return (true);
        }
        return (false);
    }
    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
}

当我试图创建会话工厂时，我得到了异常:

{"无法在类'DatabaseEntities '中找到属性'UserIdPart'的getter。UserToDo"}

CompositeId<UserToDoId>(x => x.ID)
    .KeyReference(x => x.UserIdPart, c_userID)
    .KeyReference(x => x.AchievementIdPart, c_missionID);

public class UserToDoId
{
    User UserIdPart { get; set; }
    Achievement AchievementIdPart { get; set; }
    public override bool Equals(object obj)
    {
        return Equals(obj as UserToDoId);
    }
    private bool Equals(UserToDoId other)
    {
        if (ReferenceEquals(other, null)) return false;
        if (ReferenceEquals(other, this)) return true;
        return UserIdPart.ID == other.UserIdPart.ID &&
            MissionIdPart.ID == other.MissionIdPart.ID;
    }
    public override int GetHashCode()
    {
        unchecked
        {
            int hash = GetType().GetHashCode();
            hash = (hash * 31) ^ UserIdPart.ID.GetHashCode();
            hash = (hash * 31) ^ MissionIdPart.ID.GetHashCode();
            return hash;
        }
    }
}