Entityframework cache ?

Hello,

Look at this very basic example.

Here are 2 Entity Framework models:

public class Voitures
{
public int id { get; set; }
public string nom_voiture { get; set; }

public int MarqueId { get; set; }
public Marques marque { get; set; }
}

public class Marques
{
public int id { get; set; }
public string nom_marque { get; set; }
}

And Here is a controller action method:

public IActionResult GetVoiture(int id)
{
   var voiture = bdd.voitures.FirstOrDefault(v => v.id == id);
    return Json(voiture);
}

Here is the result i get:

{"id":2,"nom_voiture":"golf","marqueId":1,"marque":null}

As you can see, the object "marque" is null.

Now, if i just add a single line in my method controller, look at the result:

public IActionResult GetVoiture(int id)
{
   var voiture = bdd.voitures.FirstOrDefault(v => v.id== id);
   var m = bdd.marques.FirstOrDefault(f => f.id == voiture.MarqueId);
   return Json(voiture);
}

You can see the marque object is not null.

{"id":2,"nom_voiture":"golf","marqueId":1,"marque":{"id":1,"nom_marque":"VW"}}

This is very strange for me because "m" variable is not assigned to nothing so i do not understand how framework can know and fetch marque object in memory...

Thanks