C# Entity Framework 4.1 Lambda Include - 仅选择特定的包含值

Question

我正在 EF4.1 上执行 lambda 选择，包括我当前语句中的另一个相关 DBSet。

 return dbEntity.GameTypes.Include(a => a.Draws)
                           .Where(d => d.IsActive == true )
                           .ToList();

我有两个类:

//simplified versions of the classes
public class GameType
{
 public Nullable<bool> IsActive { get; set; }
 public virtual ICollection<Draw> Draws { get; set; }
}

public class Draw
{
 public int DrawID { get; set; }
 public int GameTypeID { get; set; }
 public System.DateTime DrawDate { get; set; }
} 

但我只想要每个 GameType 的下一次抽奖。本质上我想做类似的事情

 return dbEntity.GameTypes.Include(a => a.Draws.Where(aw => aw.DrawDate > System.DateTime.Now)
                                               .OrderBy(ao => ao.DrawDate)
                                               .First())
                           .Where(d => d.IsActive == true )
                           .ToList();

但它给了我:

The Include path expression must refer to a navigation property defined on the type. Use dottedpaths for reference navigation properties and the Select operator for collection navigation properties.

这样的事情是可能的还是我需要在之后过滤结果？然后我还想按最新的 Draw.DrawDate 排序总结果。如果有人能告诉我正确的方法，我将不胜感激。

Answer 1

我觉得....

    from g in dbEntity.GameTypes.Include("Draws")
   where g.IsActive
     let d = g.Draws.Where(o => o.DrawDate > System.DateTime.Now)
                    .OrderBy(o => o.DrawDate)
                    .Take(1)       // Needs to stay a collection
  select new GameType {IsActive = g.IsActive, Draws = d}

未经测试 - 但它可能会让您走上正确的道路...