Question

I have a List collection that contains a List subcollection as a property within it, and I want to filter out items in that subcollection based on the value of certain properties.

To simplify, I’ll call the main collection THING and the subcollection SUBTHING. They are different types. THINGS can have 1 to many SUBTHINGS. SUBTHING has 2 properties I want to filter by, PROP1 should equal 1 (it can equal 1,2,3) and PROP2 should not be NULL (it can contain a string).

So when I use a query like the one below it seems to give me what I want (though I’m not sure All() is doing what I expect):

search = from c in search
where c.SUBTHING.All(s=>s.PROP1==1)
select c;

Then I get suspicious when I add the other property:

search = from c in search
where c.SUBTHING.All(s=>s.PROP1==1 && s.PROP2 != NULL)
select c;

And I get THINGS that have PROP2 as Null.

When I switch to Any() I lose all filtering on SUBTHING and it shows SUBTHINGS where PROP1 = 1,2,3 and where PROP2 is NULL and not NULL.

What I’m trying to get is a collection that lists all THING IDs and then lists the Name of all SUBTHINGS, sort of like this:

THING.ID
     SUBTHING.Name
     SUBTHING.Name

THING.ID
     SUBTHING.Name
     SUBTHING.Name

Is this possible to also filter SUBTHINGS while filtering THINGS with LINQ since THING and SUBTHING are two different types?

Answer 1

Try something like this:

search = 
    from c in search 
    where c.SUBTHING.All(s=>s.PROP1==1 && s.PROP2 != NULL) 
    select new {
         ThingId = c.ThingID,
         Something = c.SomeThing.Select(x=>x.Name)
     }; 

To apply filter on subitems try:

from product in products
where product.productid == 1
from image in product.productimages
where image.ismainimage
select image.imagename

From : 101 linq queries