实体框架，高效的 NavigationProperty.OfType 查询

Question

I'm having trouble constructing an efficient query in EF4 using type per table (TPT) inheritance.

I have an entity called Episode , and each episode can have multiple events. There several different type of events all deriving from a base entity called Event . I want to filter on all episodes that don't contain a certain type of event. Episode has a navigation property that is a collection of all its events (ie a collection of the base Event type)

I've tried:

from episode in context.EpisodeSet
where episode.Events.OfType<DerivedEvent>().Count() == 0
select episode

and

from episode in context.EpisodeSet
where episode.Events.Where(p => p is DerivedEvent).Count() == 0
select episode

Both of these produce a typical long SQL expansion that queries every Event type table.

Shouldn't there be a way to express this query in LINQ that just involves a join between the Episode and the DerivedEvent table in the resulting SQL?

Edit: In response to ProfessorX here is the generated SQL (basically just a typical massive union across all event tables)

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[TypeId] AS [TypeId], 
[Extent1].[PatientId] AS [PatientId], 
[Extent1].[CentreId] AS [CentreId], 
[Extent1].[CreatedOn] AS [CreatedOn], 
[Extent1].[UpdatedOn] AS [UpdatedOn], 
[Extent1].[CreatedBy] AS [CreatedBy], 
[Extent1].[UpdatedBy] AS [UpdatedBy]
FROM [dbo].[Episode] AS [Extent1]
WHERE  EXISTS (SELECT 
    1 AS [C1]
    FROM   [dbo].[Event] AS [Extent2]
    LEFT OUTER JOIN  (SELECT 
        [Extent3].[Id] AS [Id], 
        cast(1 as bit) AS [C1]
        FROM [dbo].[InvasiveDischargableEvent] AS [Extent3] ) AS [Project1] ON [Extent2].[Id] = [Project1].[Id]
    LEFT OUTER JOIN  (SELECT 
        [UnionAll4].[C1] AS [C1], 
        [UnionAll4].[C2] AS [C2], 
        [UnionAll4].[C3] AS [C3], 
        [UnionAll4].[C4] AS [C4], 
        [UnionAll4].[C5] AS [C5], 
        [UnionAll4].[C6] AS [C6], 
        [UnionAll4].[C7] AS [C7]
        FROM  (SELECT 
            [UnionAll3].[C1] AS [C1], 
            [UnionAll3].[C2] AS [C2], 
            [UnionAll3].[C3] AS [C3], 
            [UnionAll3].[C4] AS [C4], 
            [UnionAll3].[C5] AS [C5], 
            [UnionAll3].[C6] AS [C6], 
            [UnionAll3].[C7] AS [C7]
            FROM  (SELECT 
                [UnionAll2].[C1] AS [C1], 
                [UnionAll2].[C2] AS [C2], 
                [UnionAll2].[C3] AS [C3], 
                [UnionAll2].[C4] AS [C4], 
                [UnionAll2].[C5] AS [C5], 
                [UnionAll2].[C6] AS [C6], 
                [UnionAll2].[C7] AS [C7]
                FROM  (SELECT 
                    [UnionAll1].[Id] AS [C1], 
                    [UnionAll1].[C1] AS [C2], 
                    [UnionAll1].[C2] AS [C3], 
                    [UnionAll1].[C3] AS [C4], 
                    [UnionAll1].[C4] AS [C5], 
                    [UnionAll1].[C5] AS [C6], 
                    [UnionAll1].[C6] AS [C7]
                    FROM  (SELECT 
                        [Extent4].[Id] AS [Id], 
                        cast(0 as bit) AS [C1], 
                        cast(1 as bit) AS [C2], 
                        cast(0 as bit) AS [C3], 
                        cast(0 as bit) AS [C4], 
                        cast(0 as bit) AS [C5], 
                        cast(0 as bit) AS [C6]
                        FROM [dbo].[InvasivePSQ10Event] AS [Extent4]
                    UNION ALL
                        SELECT 
                        [Extent5].[Id] AS [Id], 
                        cast(0 as bit) AS [C1], 
                        cast(0 as bit) AS [C2], 
                        cast(0 as bit) AS [C3], 
                        cast(0 as bit) AS [C4], 
                        cast(0 as bit) AS [C5], 
                        cast(1 as bit) AS [C6]
                        FROM [dbo].[InvasivePostTreatmentEvent] AS [Extent5]) AS [UnionAll1]
                UNION ALL
                    SELECT 
                    [Extent6].[Id] AS [Id], 
                    cast(0 as bit) AS [C1], 
                    cast(0 as bit) AS [C2], 
                    cast(1 as bit) AS [C3], 
                    cast(0 as bit) AS [C4], 
                    cast(0 as bit) AS [C5], 
                    cast(0 as bit) AS [C6]
                    FROM [dbo].[InvasiveTreatmentEvent] AS [Extent6]) AS [UnionAll2]
            UNION ALL
                SELECT 
                [Extent7].[Id] AS [Id], 
                cast(0 as bit) AS [C1], 
                cast(0 as bit) AS [C2], 
                cast(0 as bit) AS [C3], 
                cast(0 as bit) AS [C4], 
                cast(1 as bit) AS [C5], 
                cast(0 as bit) AS [C6]
                FROM [dbo].[InvasiveConsultationEvent] AS [Extent7]) AS [UnionAll3]
        UNION ALL
            SELECT 
            [Extent8].[Id] AS [Id], 
            cast(1 as bit) AS [C1], 
            cast(0 as bit) AS [C2], 
            cast(0 as bit) AS [C3], 
            cast(0 as bit) AS [C4], 
            cast(0 as bit) AS [C5], 
            cast(0 as bit) AS [C6]
            FROM [dbo].[InvasiveMOXFQEvent] AS [Extent8]) AS [UnionAll4]
    UNION ALL
        SELECT 
        [Extent9].[Id] AS [Id], 
        cast(0 as bit) AS [C1], 
        cast(0 as bit) AS [C2], 
        cast(0 as bit) AS [C3], 
        cast(1 as bit) AS [C4], 
        cast(0 as bit) AS [C5], 
        cast(0 as bit) AS [C6]
        FROM [dbo].[InvasiveReferralEvent] AS [Extent9]) AS [UnionAll5] ON [Extent2].[Id] = [UnionAll5].[C1]
    WHERE ([Extent1].[Id] = [Extent2].[EpisodeId]) AND (CASE WHEN (( NOT (([UnionAll5].[C2] = 1) AND ([UnionAll5].[C2] IS NOT NULL))) AND ( NOT (([UnionAll5].[C3] = 1) AND ([UnionAll5].[C3] IS NOT NULL))) AND ( NOT (([UnionAll5].[C4] = 1) AND ([UnionAll5].[C4] IS NOT NULL))) AND ( NOT (([Project1].[C1] = 1) AND ([Project1].[C1] IS NOT NULL))) AND ( NOT (([UnionAll5].[C5] = 1) AND ([UnionAll5].[C5] IS NOT NULL)))) THEN '2X' WHEN (([UnionAll5].[C5] = 1) AND ([UnionAll5].[C5] IS NOT NULL)) THEN '2X0X' WHEN (([Project1].[C1] = 1) AND ([Project1].[C1] IS NOT NULL) AND ( NOT (([UnionAll5].[C6] = 1) AND ([UnionAll5].[C6] IS NOT NULL))) AND ( NOT (([UnionAll5].[C7] = 1) AND ([UnionAll5].[C7] IS NOT NULL)))) THEN '2X1X' WHEN (([UnionAll5].[C4] = 1) AND ([UnionAll5].[C4] IS NOT NULL)) THEN '2X2X' WHEN (([UnionAll5].[C2] = 1) AND ([UnionAll5].[C2] IS NOT NULL)) THEN '2X3X' WHEN (([UnionAll5].[C6] = 1) AND ([UnionAll5].[C6] IS NOT NULL)) THEN '2X1X0X' WHEN (([UnionAll5].[C7] = 1) AND ([UnionAll5].[C7] IS NOT NULL)) THEN '2X1X1X' ELSE '2X4X' END LIKE '2X4X%')
)

Answer 1

After much head scratching I've managed to get this to work:

var episodes = (from episode in context.EpisodeSet
                join e in context.EventSet.OfType<DerivedEvent>() on episode.Id equals e.EpisodeId into outer
                from o in outer.DefaultIfEmpty()
                where o == null
                select episode)

So rather than try to apply an OfType filter to the navigation property I've had to apply it to the ObjectSet and do an outer join. Seems that OfType and 'as' type filtering don't work against Navigation Properties.

This produces the episodes that don't have a corresponding event in the DerivedEvent table, and with the kind of SQL that you would write by hand.

The LINQ follows the way you'd naturally write the query with SQL. It's just too easy to get seduced by all these navigation properties that lead to nice looking LINQ but awful looking SQL.

Answer 2

.Any() is better than.Count() From my prospective your query can be optimized to:

context.EpisodeSet
.Where(e => e.Events.Any(p => p is DerivedEvent))
.Select(e => e);