由.Include（）相关实体创建的内部联接的IQueryable Count（）方法问题

Question

IQueryable<EntityOne> query = entities.EntityOne
    .Include(t => t.EntityRelated1)
    .Include(t => t.EntityRelated2)
    .AsQueryable();

The query generated in "query" variable :

SELECT 
[Extent1].[Id] AS [IdEntityOne], 
 ...
[Extent2].[Id] AS [IdEntityRelatedOne], 
...
[Extent3].[Id] AS [IdEntityRelatedTwo], 
...
FROM   [dbo].[EntityOne] AS [Extent1]
   INNER JOIN [dbo].[EntityRelatedOne] AS [Extent2]
       ON [Extent1].[IdRelatedOne] = [Extent2].[Id]
   INNER JOIN [dbo].[EntityRelatedTwo] AS [Extent3]
       ON [Extent1].[IdRelatedTwo] = [Extent3].[Id]

After that, on C# code those are the result of counting:

var wrongCount = query.Count(); // Returns 295
var correctCount = query.AsEnumerable().Count(); // Returns 10

The 295 count is the full EntityOne set numbers of registers. (wrong)

The 10 Count is the desired count after Inner Join.

It sounds like the IQueryable.Count() is counting before executing the InnerJoin on database. I don't want to generate the IEnumerable since I hope the count to be executed on Sql Server together with the inner join.

UPDATE 1

Trying to manually execute the inner join:

IQueryable<EntityOne> query2 = entities.EntityOne.Join(entities.EntityTwo,
     eone=> eone.IdRelatedOne, en => en.Id,
     (x, y) => x);

The SQL code generated in "query2" is :

SELECT 
[Extent1].[Id] AS [Id], 
...
FROM [dbo].[EntityOne] AS [Extent1]

As you can see, the related entity is not included on Inner Join forced by linq Join statement.

Update 2

I dont know if it matters but, the IdEntityRelated1 on EntityOne is a required property, plus its not a foreign key on database, just a Integer field that stores the Id of the related entity. (Im working with POCO classes with Database First)

I have another working sources where fields but they're nullable integers instead of required. Maybe should I not try to do an Include to force Inner Join between required relationships?

Answer 1

You have a required association, but the expected objects are not present in the database.

But let's first see what EF does.

In the first count ...

var wrongCount = query.Count();

...the Include s are ignored. There's no reason to execute them because EF has been told that the referred objects ( EntityRelated1 and EntityRelated2 are mandatory, so inner joins are expected to find the related records . If they do, EF figures it may as well just count entities.EntityOne and skip the rest. The Includes are only going to make the query more expensive and they don't affect the result.

You can check that by monitoring the SQL that's executed for the count. That's not the SQL generated when you look at query only! It's probably something that simply boils down to

SELECT COUNT(*) FROM [dbo].[EntityOne]

So the first count returns a correct count of all EntityOne records in the database.

For the second count you force execution of the entire query that's stored in the query variable, the SQL statement that you show. Then you count its results in memory – and it returns 10 . This means that the query with the inner joins does actually return 10 records. That, in turn, can only mean one thing: there are 285 EntityOne.IdRelatedOne values that don't point to an existing EntityRelatedOne record. But you mapped the association as required, so EF generates an inner join. An outer join would also return 295.

Answer 2

Include is not a LINQ method proper, is an EntityFramework extension designed to do eager loading and not much else. Include s are lost if the query shape changes :

When you call the Include method, the query path is only valid on the returned instance of the IQueryable of T. Other instances of IQueryable of T and the context itself are not affected.

Specifically this means that, for instance aggregates on top of the Include d IQueryable<T> are going to loose the Include (which is exactly what you see).

See Tip 22 - How to make Include really Include , IQueryable.Include() gets ignored , Include in following query does not include really and many more.