我一直在尝试让以下Linq工作，没有快乐。我确信它是对的，但那可能只是我的坏Linq。我最初在这里添加了这个作为类似问题的答案：
Linq-to-entities - Include() method not loading
但由于这是一个非常古老的问题，而且我的问题更具体，我认为它会作为一个明确的问题做得更好。
在链接的问题中，Alex James提供了两个有趣的解决方案，但是如果你尝试并检查SQL，那就太可怕了。
我正在研究的例子是：
var theRelease = from release in context.Releases
where release.Name == "Hello World"
select release;
var allProductionVersions = from prodVer in context.ProductionVersions
where prodVer.Status == 1
select prodVer;
var combined = (from release in theRelease
join p in allProductionVersions on release.Id equals p.ReleaseID
select release).Include(release => release.ProductionVersions);
var allProductionsForChosenRelease = combined.ToList();
这遵循两个例子中较简单的一个。没有包含它会产生完全可敬的sql：
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name]
FROM [dbo].[Releases] AS [Extent1]
INNER JOIN [dbo].[ProductionVersions] AS [Extent2] ON [Extent1].[Id] = [Extent2].[ReleaseID]
WHERE ('Hello World' = [Extent1].[Name]) AND (1 = [Extent2].[Status])
但是，OMG：
SELECT
[Project1].[Id1] AS [Id],
[Project1].[Id] AS [Id1],
[Project1].[Name] AS [Name],
[Project1].[C1] AS [C1],
[Project1].[Id2] AS [Id2],
[Project1].[Status] AS [Status],
[Project1].[ReleaseID] AS [ReleaseID]
FROM ( SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name],
[Extent2].[Id] AS [Id1],
[Extent3].[Id] AS [Id2],
[Extent3].[Status] AS [Status],
[Extent3].[ReleaseID] AS [ReleaseID],
CASE WHEN ([Extent3].[Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM [dbo].[Releases] AS [Extent1]
INNER JOIN [dbo].[ProductionVersions] AS [Extent2] ON [Extent1].[Id] = [Extent2].[ReleaseID]
LEFT OUTER JOIN [dbo].[ProductionVersions] AS [Extent3] ON [Extent1].[Id] = [Extent3].[ReleaseID]
WHERE ('Hello World' = [Extent1].[Name]) AND (1 = [Extent2].[Status])
) AS [Project1]
ORDER BY [Project1].[Id1] ASC, [Project1].[Id] ASC, [Project1].[C1] ASC
垃圾总量。这里要注意的关键点是它返回表的外连接版本，该版本不受status = 1的限制。
这会导致返回错误的数据：
Id Id1 Name C1 Id2 Status ReleaseID
2 1 Hello World 1 1 2 1
2 1 Hello World 1 2 1 1
请注意，尽管我们有限制，但仍会在那里返回2的状态。它根本不起作用。 如果我在某个地方出错了，我会很高兴发现，因为这是对Linq的嘲弄。我喜欢这个想法，但目前执行似乎并不可用。
出于好奇，我尝试了LinqToSQL dbml，而不是产生上述混乱的LinqToEntities edmx：
SELECT [t0].[Id], [t0].[Name], [t2].[Id] AS [Id2], [t2].[Status], [t2].[ReleaseID], (
SELECT COUNT(*)
FROM [dbo].[ProductionVersions] AS [t3]
WHERE [t3].[ReleaseID] = [t0].[Id]
) AS [value]
FROM [dbo].[Releases] AS [t0]
INNER JOIN [dbo].[ProductionVersions] AS [t1] ON [t0].[Id] = [t1].[ReleaseID]
LEFT OUTER JOIN [dbo].[ProductionVersions] AS [t2] ON [t2].[ReleaseID] = [t0].[Id]
WHERE ([t0].[Name] = @p0) AND ([t1].[Status] = @p1)
ORDER BY [t0].[Id], [t1].[Id], [t2].[Id]
略微更紧凑 - 怪异的计数条款，但整体相同的总失败。
请告诉我，我错过了一些明显的东西，因为我真的很想要Linq！
答案 0 :(得分：0)
好的，经过另一个搔痒的夜晚，我破了它。
在LinqToSQL中：
using (var context = new TestSQLModelDataContext())
{
context.DeferredLoadingEnabled = false;
DataLoadOptions ds = new DataLoadOptions();
ds.LoadWith<ProductionVersion>(prod => prod.Release);
context.LoadOptions = ds;
var combined = from release in context.Releases
where release.Name == "Hello World"
select from prodVer in release.ProductionVersions
where prodVer.Status == 1
select prodVer;
var allProductionsForChosenRelease = combined.ToList();
}
这会产生更合理的SQL：
SELECT [t2].[Id], [t2].[Status], [t2].[ReleaseID], [t0].[Id] AS [Id2], [t0].[Name], (
SELECT COUNT(*)
FROM [dbo].[ProductionVersions] AS [t3]
WHERE ([t3].[Status] = 1) AND ([t3].[ReleaseID] = [t0].[Id])
) AS [value]
FROM [dbo].[Releases] AS [t0]
OUTER APPLY (
SELECT [t1].[Id], [t1].[Status], [t1].[ReleaseID]
FROM [dbo].[ProductionVersions] AS [t1]
WHERE ([t1].[Status] =1) AND ([t1].[ReleaseID] = [t0].[Id])
) AS [t2]
WHERE [t0].[Name] = 'Hello World'
ORDER BY [t0].[Id], [t2].[Id]
产生正确的结果：
Id Status ReleaseID Id2 Name value
2 1 1 1 Hello World 1
在LinqToEntities中（我无法使Include语法起作用，所以我使用了结果中包含所需表格的怪癖）：
using (var context = new TestEntities1()) { var combined = (from release in context.Releases where release.Name == "Hello World" select from prodVer in release.ProductionVersions where prodVer.Status == 1 select new { prodVer, Release =prodVer.Release }); var allProductionsForChosenRelease = combined.ToList(); }
这会产生SQL：
SELECT
[Project1].[Id] AS [Id],
[Project1].[C1] AS [C1],
[Project1].[Id1] AS [Id1],
[Project1].[Status] AS [Status],
[Project1].[ReleaseID] AS [ReleaseID],
[Project1].[Id2] AS [Id2],
[Project1].[Name] AS [Name]
FROM ( SELECT
[Extent1].[Id] AS [Id],
[Join1].[Id1] AS [Id1],
[Join1].[Status] AS [Status],
[Join1].[ReleaseID] AS [ReleaseID],
[Join1].[Id2] AS [Id2],
[Join1].[Name] AS [Name],
CASE WHEN ([Join1].[Id1] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM [dbo].[Releases] AS [Extent1]
LEFT OUTER JOIN (SELECT [Extent2].[Id] AS [Id1], [Extent2].[Status] AS [Status], [Extent2].[ReleaseID] AS [ReleaseID], [Extent3].[Id] AS [Id2], [Extent3].[Name] AS [Name]
FROM [dbo].[ProductionVersions] AS [Extent2]
INNER JOIN [dbo].[Releases] AS [Extent3] ON [Extent2].[ReleaseID] = [Extent3].[Id] ) AS [Join1] ON ([Extent1].[Id] = [Join1].[ReleaseID]) AND (1 = [Join1].[Status])
WHERE 'Hello World' = [Extent1].[Name]
) AS [Project1]
ORDER BY [Project1].[Id] ASC, [Project1].[C1] ASC
这是相当精神上的，但确实有效。
Id C1 Id1 Status ReleaseID Id2 Name
1 1 2 1 1 1 Hello World
所有这些都让我得出Linq远未完成的结论。它可以使用，但要非常谨慎。使用它作为强类型和编译时检查，但是很费力/容易出错，编写错误的SQL的方法。这是一种权衡。你在C＃端获得了更多的安全性，但是比编写SQL要困难得多！
答案 1 :(得分：0)
再看看，我现在明白了Include的难以捉摸的效果。
正如在纯SQL中一样，当连接的右侧是＆＃34; n＆＃34;时，LINQ中的连接将重复结果。结束1-n关联。
假设您有一个Release，其中有两个ProductionVersion。如果没有Include，则连接将为您提供两个相同的Release，因为在所有语句select发布之后。现在，当您添加Include时，EF不仅会返回两个版本，还会完全填充其ProductionVersions个集合。
更深入一点，在上下文缓存中，看起来EF实际上只实现了1 Release和2 ProductionVersion s。它只是在最终结果集中返回两次。
在某种程度上，你得到了你要求的东西：给我发布，乘以他们的版本数量。但那不是你想要的要求的。
你（可能）想要揭示EF工具箱中的弱点：我们不能Include部分收藏。我认为您尝试仅使用ProductionVersions = 1的Status填充版本。如果可能的话，你宁愿这样做：
context.Releases.Include(r => r.ProductionVersions.Where(v => v.Status == 1))
.Where(r => r.Name == "Hello World")
但这引发了一个例外：
Include路径表达式必须引用在类型上定义的导航属性。使用虚线路径作为参考导航属性，使用Select运算符作为集合导航属性。 参数名称：路径
此＆＃34;过滤包括＆＃34;在EF团队（或贡献者）决定抓住this issue之前，我们已经注意到问题，我们必须采用精心设计的解决方法。我描述了一个常见的here。