EF Core - TPH: Include child properties

Question

I am trying to find how to include navigation properties of dervied type.

The example:

public abstract class BaseType
{
   public int Key {get;}
{

public class FirstChild : BaseType
{
   public Link Link { get; }
}

public class Link
{
   
}

I would like to get all instances of BaseType using one query. I can do simply:

DbContext.BaseTypes.ToList()

However I would like to get all instances plus include FirstChild.Link

I cannot do

DbContext.BaseTypes.Include(x => x.Link).ToList()

What I found on SO is to use two separate queries. Is it achivable from one query ( using casting ? ).

Answer 1

This is shown in the docs, in Include on derived types in the Eager Loading docs. If you have Person and Student types like these:

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Student : Person
{
    public School School { get; set; }
}

public class School
{
    public int Id { get; set; }
    public string Name { get; set; }

    public List<Student> Students { get; set; }
}

You can include student schools by casting in the Include call :

context.People.Include(person => ((Student)person).School).ToList()

Or you can specify the navigation property by name :

context.People.Include("School").ToList()