но даже без него понятно, что LINQ в качестве ОRM рассматривать не стоит.

db.Categories
    .Select(c=> 
         new {
              Category = c,
              Products = db.Products.Where(p=>p.CategoryID==c.CategoryID)
         });

db.Table.OrderBy(p=>p.SortField).Take( 30 ).Select(p=>new MyObj() {..})

SELECT field1,field2,...
FROM (
    SELECT TOP ( 30 ) field1,field2,...
    FROM [dbo].[Table] AS [t0]
    ORDER BY [t0].[SortField]
    ) AS [t1]
ORDER BY [t1].[SortField]

SELECT field1,field2, ..., (
    SELECT COUNT(*)
    FROM (
        SELECT NULL AS [EMPTY]
        FROM [dbo].[SubTable] AS [t4]
        WHERE [t4].[SubTable.pr_id] = [t2].[id]
        ) AS [t5]
    ) AS [value]
FROM (
    SELECT t1.field1,t1.field2,..., [t1].[ROW_NUMBER]
    FROM (
        SELECT ROW_NUMBER() OVER (ORDER BY [t0].[SortField], [t0].[id]) AS [ROW_NUMBER], ...
        FROM [dbo].[Table] AS [t0]
        ) AS [t1]
    WHERE [t1].[ROW_NUMBER] BETWEEN @p0 +  1  AND @p0 + @p1
    ) AS [t2]
LEFT OUTER JOIN [dbo].[SubTable] AS [t3] ON [t3].[pr_id] = [t2].[id]
ORDER BY [t2].[ROW_NUMBER], [t3].[id]