Linq多级内部联接

Question

I have 3 diffferent entities:

E1, E2, E3

E1 has a property that is an ObservableCollection of E2. E2 has a property that is an ObservableCollection of E3.

And with a linq query, I want to get all E3 based on E1 I got as starting point.

I tried something like that :

Query = Query.Where<E3>(i => E1.E2List.Select(ep => ep.E3List.Select(ai => ai.id))
             .Contains(i.id));

Basically meaning : getting all E3 where it's id is in the list of E3 in the lists of E2 from E1

But as you guess, this doesn't work.

My starting point is this :
//make the array 
E3[] array;
//get all E3 datas
IQueryable<E3> Query = DBSetE3.AsQueryable();

And I must have all the results in my array

So my result should be : getting in array, all E3 objects that are linked into E2 that are contains into E1, based on E1.

For example :

Entity 1| List of E2
E1 | E2A, E2B

Entity 2 | List of E3
E2B | E3C, E3D
E2A | E3E, E3F

When I search for E3 linked to E1, I must get E3C, E3D,E3E,E3F

Answer 1

You can do something like this:

var e1Ids = new [] { 1, 2, 3 };
var e3s = DBSetE1.AsQueryable().Where(e => e1Ids.Contains(e.Id))
                               .SelectMany(e => e.E2List)
                               .SelectMany(e => e.E3List);

Basically, you filter all the E1's based on your input. Then you want to SelectMany (which flattens the the result [[1,2],[3,4]] into [1,2,3,4] ) to grab the E2s. Then you SelectMany it's E3s.