How to Lambda in Extension Methods with Multiple Lists?

Question

There are the following Objects:

public class Objeto1
{
   public List<Objeto2> PropObj1 {get; set;}
}

public class Objeto2
{
   public List<Objeto3> PropObj2 {get; set;}
}

public class Objeto3
{
   public int PropObj3 {get; set;}
}

I have a List of Object1 and I need to get a filtered list of Object 1, only those who possess the Propobj3 == 1:

List<Objeto1> listaObj1 = new List<Objeto1>();
// Suponhamos que listaObj1 já possui valores inseridos.

var resultado = listaObj1.Where(o1 => o1.PropObj1... ).ToList();

In this case, what would the expression lambda look like?
I’m using Entity Framework.

Answer 1

If it’s Entity Framework, I think the list comes from a context, then I won’t use a separate list to answer. I will answer from the same context, because the construction of a list from a data context is completely different from the construction of a list from an operation in memory using Linq:

var lista = contexto.Objetos1
                  .Where(o1 => o1.PropObj1
                                 .Any(o2 => o2.PropObj2
                                              .Any(o3 => o3.PropObj3 == 1)))
                  .ToList();

In pure Linq, see that it would look different:

var sublist = list.PropObj1
                  .Where(o => o.PropObj2.Any(o2 => o2.PropObj3 == 1))
                  .ToList();

I rode you a Fiddle.

Answer 2

I think this is what you want:

var resultado = listaObj1
    .SelectMany(o => o.PropObj1, (objeto1, objeto2) => new { objeto1, objeto2 })
    .SelectMany(o => o.objeto2.PropObj2, (objeto2, objeto3) => new { objeto2, objeto3 })
    .Where(o => o.objeto3.PropObj3 == 1).Select(o => new { o.objeto2.objeto1.PropObj1 })
    .ToList();

SelectMany() serves to transform list lists into a single sequential list.

Eventually you need to use one Select() to determine how either the result.

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.