实体框架代码优先 - 多对多过滤

Question

小EF问题。 我在EF中映射了多对多关系。 X.Y 所以当我有一个X有一个属性X.Ys.

现在我想要做的是使用LINQ查询得到一些X的，但我不希望有所有的Y的选择X的内部。 我想Y's过滤Y.RegistrationDate> Date.Today。

所以，当我有一个X，并通过.Y's，我只会得到未来的Y's。

UPDATE 这工作，导致S中有与它的关系只包含即将举行的活动不同微克的。 但不要告诉我这个不能简化??！

 var t = (from ug in uof.Ugs.All().ToList() 
       from upcomingEvent in ug.Events 
       where upcomingEvent.Date >= DateTime.Today 
       select new 
       { 
        ug, 
        upcomingEvent 
       }).ToList(); 

     var s = (from ug in t.Select(x => x.ug).Distinct() 
       select new UG 
       { 
        Id = ug.Id, 
        Name = ug.Name, 
        Description = ug.Description, 
        WebSite = ug.WebSite, 
        Events = ug.Events.Where(x => x.Date >= DateTime.Today).ToList() 
       }).ToList(); 

UPDATE2

添加的图像显示，即使基本脉络操纵我仍然得到2个事件，事件的时候我拿1！只要你想它

exampledebugimage

Answer 1

你有没有试过？：

var query = Xs 
.Select(x => new { x, yCol = x.YCol.Where(y => y.Date >= DateTime.Today) }) 
.AsEnumerable() 
.Select(x => x.x) 
.ToList(); 

参见：http://blogs.msdn.com/b/alexj/archive/2009/10/13/tip-37-how-to-do-a-conditional-include.aspx

所有这些.ToList使用将意味着你过滤之前，从数据库加载整个表。所以要注意这一点。

UPDATE：作为修正不工作的许多一对多

作为Slauma在评论中提到要确保，如果你要提交变化您不使用这种技术更改跟踪会认为你改变了收藏。或者甚至更好的确保你使用.AsNoTracking（），无论如何它都会提高性能。

我们可以使用与上述相同的解决方案，但对于多对多略有不同。看到这个例子：

[TestClass] 
public class ContextTest 
{ 
    [TestMethod] 
    public void FixupTest() 
    { 
     Database.SetInitializer(new DropCreateDatabaseAlways<Context>()); 

     using (var db = new Context()) 
     { 
      db.Groups.Add(new Group 
      { 
       Name = "G1", 
       Users = new List<User>{ 
        new User{ Name = "M"}, 
        new User{Name = "S"} 
       } 
      }); 

      db.SaveChanges(); 
     } 

     using (var db = new Context()) 
     { 
      var group = db.Groups 
       .Select(g => new { g, Users = g.Users.Where(u => u.Name == "M") }) 
       .AsEnumerable() 
       .Select(g => { 
        g.g.Users = g.Users.ToList(); 
        return g.g; 
       }) 
       .First(); 

      Assert.AreEqual(1, group.Users.Count); 
     } 
    } 


} 



public class User 
{ 
    public int ID { get; set; } 
    public string Name { get; set; } 

    public ICollection<Group> Groups { get; set; } 
} 



public class Group 
{ 
    public int ID { get; set; } 
    public string Name { get; set; } 

    public ICollection<User> Users { get; set; } 
} 

测试通过而产生的SQL是：

SELECT 
[Project1].[ID] AS [ID], 
[Project1].[Name] AS [Name], 
[Project1].[C1] AS [C1], 
[Project1].[ID1] AS [ID1], 
[Project1].[Name1] AS [Name1] 
FROM (SELECT 
    [Extent1].[ID] AS [ID], 
    [Extent1].[Name] AS [Name], 
    [Join1].[ID] AS [ID1], 
    [Join1].[Name] AS [Name1], 
    CASE WHEN ([Join1].[Group_ID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1] 
    FROM [dbo].[Groups] AS [Extent1] 
    LEFT OUTER JOIN (SELECT [Extent2].[Group_ID] AS [Group_ID], [Extent3].[ID] AS [ID], [Extent3].[Name] AS [Name] 
     FROM [dbo].[GroupUsers] AS [Extent2] 
     INNER JOIN [dbo].[Users] AS [Extent3] ON [Extent3].[ID] = [Extent2].[User_ID]) AS [Join1] ON ([Extent1].[ID] = [Join1].[Group_ID]) AND (N'Mikael' = [Join1].[Name]) 
) AS [Project1] 
ORDER BY [Project1].[ID] ASC, [Project1].[C1] ASC 

Answer 2

EF不支持这种情况下，是什么，但是你可以做的是：

var date = DateTime.Date; 
var query = from x in Xs     
      select new 
      { 
       X = x 
       Ys = x.Ys.Where(i = > i.RegistrationDate > date) 
      } 

，这将给你X的集合与他们对应的Y的比赛你那标准。