Question

I am working in an ASP.NET project with EF and I have some trouble with finding a correct query.
I need to work without lazy-loading.

I have following data structure:
A Module contains pages.
A Page contains PageItems.
A PageItem contains an Item.
An Item can contains other Items.

Leaving out the recursive aspect of Items containing Items at first, I need a query to feed the structure of a single module into a treeview.

What I want is :

• The Module with the given ID
  • Including all pages
    • Including all PageItems
      • Including all Items with ParentItem_ID == 0
        • Including all ChildItems

I started with this:

return base._entities.Modules
            .Include(m => m.Paginas
                .Select(p => p.PaginaItems
                    .Select(pi => pi.Item)
                    .Select(i => i.ChildItems)))
            .Where(m => m.Module_ID == id)
            .FirstOrDefault();

This query works, but it ignores the item-hierarchy and displays all items as direct child of a page. What would actually need is something like this:

return base._entities.Modules
           .Include(m => m.Paginas
               .Select(p => p.PaginaItems
                   .Select(pi => pi.Item)
                   .Where(i => i.I_ParentItem_ID == 0)
                   .Select(i => i.ChildItems)))
           .Where(m => m.Module_ID == id)
           .FirstOrDefault();

But it does not work.

I an relatively new to LINQ, and any help would really be appreciated.

Answer 1

As you need a condition in a nested collection you should use join, like:

(from mod in c.Modules
join pag in c.Paginas on mod.Module_Id equals pag.Module_Id
join pi in c.PaginaItems on pag.Pagina_Id equals pi.Pagina_Id
join item in c.Items.Where(i => i.I_ParentItem_ID == 0) on pi.PaginaItem_Id
    equals item.PaginaItem_Id
join ci in c.ChildItems on item.I_ParentItem_ID equals ci.I_ParentItem_ID
select mod).FirstOrDefault()

I abbreviated base._entities to c (for context) and made some assumptions about Id names and possibly overlooked the odd syntax error, but this should be a good start.