c# – 实体框架 – 无法使LEFT OUTER加入工作

请参阅下面的2个版本的代码和它生成的sql.我想加载首选项,但我也想只带我的用户首选项,因此我使用WHERE子句.但是一旦我把它放进Go – 我就不再让OUTER加入了.为什么？

var query = from p in context.Preferences
                            join up in context.UserPreferences on p.PreferenceKey equals up.PreferenceKey into outer
                            from up in outer.DefaultIfEmpty()
                            select new MobileRESTEntities.UserPreference
                            {
                                CreatedOn = (up == null) ? p.CreatedOn : up.CreatedOn,UpdatedOn = (up == null) ? p.CreatedOn : (up.UpdatedOn ?? up.CreatedOn),PreferenceId = p.PreferenceId,Value = (up == null) ? p.ValueDefault : up.Value,};

使用WHERE：

var query = from p in context.Preferences
                            join up in context.UserPreferences on p.PreferenceKey equals up.PreferenceKey into outer
                            from up in outer.DefaultIfEmpty()
                            where up.UserKey.Equals((int)user.ProviderUserKey)
                            &&
                            (
                            (up == null)
                            ||
                            ((up.UpdatedOn > lastSyncOn && up.UpdatedOn != null) || (up.CreatedOn > lastSyncOn))
                            )
                            select new MobileRESTEntities.UserPreference
                            {
                                CreatedOn = (up == null) ? p.CreatedOn : up.CreatedOn,};

没有WHERE – GOOD

SELECT 
[Extent1].[PreferenceKey] AS [PreferenceKey],CASE WHEN ([Extent2].[UserPreferenceKey] IS NULL) THEN [Extent1].[CreatedOn] ELSE [Extent2].[CreatedOn] END AS [C1],CASE WHEN ([Extent2].[UserPreferenceKey] IS NULL) THEN [Extent1].[CreatedOn] WHEN ([Extent2].[UpdatedOn] IS NULL) THEN [Extent2].[CreatedOn] ELSE [Extent2].[UpdatedOn] END AS [C2],[Extent1].[PreferenceId] AS [PreferenceId],CASE WHEN ([Extent2].[UserPreferenceKey] IS NULL) THEN [Extent1].[ValueDefault] ELSE [Extent2].[Value] END AS [C3]
FROM  [dbo].[MBLPreference] AS [Extent1]
LEFT OUTER JOIN [dbo].[MBLUserPreference] AS [Extent2] ON [Extent1].[PreferenceKey] = [Extent2].[PreferenceKey]

随着WHERE – 坏 – 没有外部加入

exec sp_executesql N'SELECT 
[Extent1].[PreferenceKey] AS [PreferenceKey],[Extent2].[CreatedOn] AS [CreatedOn],CASE WHEN ([Extent2].[UpdatedOn] IS NULL) THEN [Extent2].[CreatedOn] ELSE [Extent2].[UpdatedOn] END AS [C1],[Extent2].[Value] AS [Value]
FROM  [dbo].[MBLPreference] AS [Extent1]
INNER JOIN [dbo].[MBLUserPreference] AS [Extent2] ON [Extent1].[PreferenceKey] = [Extent2].[PreferenceKey]
WHERE ([Extent2].[UserKey] = @p__linq__0) AND ((1 = 0) OR (([Extent2].[UpdatedOn] > @p__linq__1) AND ([Extent2].[UpdatedOn] IS NOT NULL)) OR ([Extent2].[CreatedOn] > @p__linq__2))',N'@p__linq__0 int,@p__linq__1 datetime2(7),@p__linq__2 datetime2(7)',@p__linq__0=15,@p__linq__1='0001-01-01 00:00:00',@p__linq__2='0001-01-01 00:00:00'

编辑

是的,WHERE将无法正常工作,但我的sql应该看起来像：

SELECT P.*
FROM dbo.MBLPreference P
LEFT OUTER JOIN dbo.MBLUserPreference UP ON P.PreferenceKey = UP.PreferenceKey
AND UP.UserKey = 8 AND UP.CreatedOn > '1-1-1'

我该如何编写LINQ来实现这一目标？

回答

这就是我需要做的事情(将条件移到连接本身)

var query = from p in context.Preferences
                            join up in context.UserPreferences
                            .Where(x => 
                                x.UserKey.Equals((int)user.ProviderUserKey)
                                &&
                                ((x.UpdatedOn > lastSyncOn && x.UpdatedOn != null) || (x.CreatedOn > lastSyncOn))
                                ) 
                            on p.PreferenceKey equals up.PreferenceKey into outer
                            from up in outer.DefaultIfEmpty() 
                            select new MobileRESTEntities.UserPreference
                            {
                                CreatedOn = (up == null) ? p.CreatedOn : up.CreatedOn,};

解决方法

我不确定你想要达到的目标,但我相信你需要在以下情况下调整条件： 来自p在上下文中.参考     加入context.UserPreferences.Where(x => x.UserKey == user.ProviderUserKey&&     (//你的其他条件)      )     进入外…