LINQ to SQL and a separate table

Question

The dbml file contains the following test model:

Model http://www.freeimagehosting.net/uploads/a86582498a.gif

In the test case, the table has 4 entries, 1 parent, 3 children. We are looking for siblings for a particular record, including a specific record.

using (var db = new TestDataContext())
{
    var query = 
        from f in db.Foos
        where f.Name == "Two"
        select f.Foo1.Foos;              // get the record parent children

    var foos = query.SelectMany(f => f); // project the EntitySet

    Assert.AreEqual(3, foos.Count());    // passes
}

This returns the correct elements with the following SQL:

SELECT     [t2].[FooId], 
           [t2].[ParentFooId], 
           [t2].[Name]
FROM       [dbo].[Foos] AS [t0]
INNER JOIN [dbo].[Foos] AS [t1] ON [t1].[FooId] = [t0].[ParentFooId]
CROSS JOIN [dbo].[Foos] AS [t2]
WHERE      ([t0].[Name] = @p0) 
AND        ([t2].[ParentFooId] = [t1].[FooId])

We wonder about CROSS JOIN, is this apparently the result of SelectMany?
Is there any other way we should approach in order not to have CROSS-JOIN?

Answer 1

You can add data from statements in a Linq query, and this will probably help you here.

var query = from f in db.Foos
            from f2 in f.Foos
            where f.Name == "Two"
            select f2;

What produces.

SELECT [t1].[FooId],
       [t1].[Name],
       [t1].[ParentFooId]
FROM [dbo].[Foos] AS [t0], [dbo].[Foos] AS [t1]
WHERE ([t0].[Name] = @p0) AND ([t1].[ParentFooId] = [t0].[FooId])

Answer 2

:

var query = from f in db.Foos
            where (from fo in db.Foos
                   where fo.Name == "Two"
                   select fo.ParentId).Contains(f.ParentId)
            select f;

- :

SELECT     [t1].[FooId], 
           [t1].[ParentFooId], 
           [t1].[Name]
FROM       [dbo].[Foos] AS [t1]
WHERE      [t1].[ParentFooId] IN (SELECT [t0].[ParentFooId]
                                  FROM [dbo].[Foos] AS [t0]
                                  WHERE[t0].[Name] = @p0)

(, Exists() )... .

Answer 3

Try the following:

var siblings = DataContext.Foos.Where(a => a.FooID == 3)
    .Select(b => Foos.Where(b => Foos.ParentFooID == a.ParentFooID));

Assert.AreEqual(3, siblings.Count());