Parent navigation property is `null` when selecting child object

Question

I have two classes that partake in a parent-child relationship. The parent class is Country, and the child class is City:

public partial class Country
{
    public Country()
    {
        this.Cities = new List<City>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public string AlphaCodeTwo { get; set; }
    public string AlphaCodeThree { get; set; }
    public Nullable<int> NumericCode { get; set; }
    public string Capital { get; set; }
    public string Nationality { get; set; }
    public Nullable<decimal> CapitalArea { get; set; }
    public Nullable<decimal> CapitalPopulation { get; set; }
    public string Image { get; set; }
    public virtual List<City> Cities { get; set; }
}

public partial class City
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Code { get; set; }
    public Nullable<int> NumericCode { get; set; }
    public virtual Country Country { get; set; }
}

When I select a City object with the following LINQ query, the navigation property to the parent class is null:

private List<Country> _Country;
var City = _Country.SelectMany(c => c.Cities).OrderBy(ci => ci.Name).ToList();

I get all children, but no parent data.

How you add city to country? Are you sure you set Country property of city — Roman G., Sep 17 '14 at 20:15
you linq is selecting a flat list of all cities in all countries in the _Country list, when you say Parent data I am unsure what you mean, do you mean the virtual Country property on each city object is null? — Pharabus, Sep 17 '14 at 20:17
i have json data in a file, and this object have all the data now ,so i want get the all city object contaning country in his navigation property — Developerzzz, Sep 17 '14 at 20:18
You want to .Include() the parents. LINQ will not automatically load related entities, because that could break a lot of stuff. See http://msdn.microsoft.com/en-us/library/bb738708(v=vs.110).aspx — Guillaume CR, Sep 17 '14 at 20:18
@Pharabus yes virtual Country Property is null in city Object — Developerzzz, Sep 17 '14 at 20:19
I suspect Guillaume has the right answer though without seeing how you populate the data initially it is hard to say — Pharabus, Sep 17 '14 at 20:22
@GuillaumeCR: The question is tagged `linq-to-objects`. So we're not talking about Entity Framework here. (Unless the OP chose the wrong tag.) — stakx - no longer contributing, Sep 17 '14 at 20:42
as i mention that I have json file and I fetch it and then save it in the _Country field so how I can make Include() — Developerzzz, Sep 18 '14 at 08:16

score 1 · Answer 1 · answered Sep 17 '14 at 20:25

If you're using Entity Framework, you can use .Include() to grab the navigation property data as you load the objects. Note that it tends to produce some pretty gnarly queries.

var city = (
    from c in db.Cities.Include(c => c.Country)
    where c.CountryId == CountryId
    orderby c.Name
    select c
).ToList();

Parent navigation property is `null` when selecting child object

1 Answers1