Q:

How to include a child object's child object in Entity Framework 5

I am using Entity Framework 5 code first and ASP.NET MVC 3.
I am struggling to get a child object's child object to populate.  Below are my classes..
Application class;
public class Application
{
     // Partial list of properties

     public virtual ICollection<Child> Children { get; set; }
}

Child class:
public class Child
{
     // Partial list of properties

     public int ChildRelationshipTypeId { get; set; }

     public virtual ChildRelationshipType ChildRelationshipType { get; set; }
}

ChildRelationshipType class:
public class ChildRelationshipType
{
     public int Id { get; set; }

     public string Name { get; set; }
}

Part of GetAll method in the repository to return all the applications:
return DatabaseContext.Applications
     .Include("Children");

The Child class contains a reference to the ChildRelationshipType class.  To work with an application's children I would have something like this:
foreach (Child child in application.Children)
{
     string childName = child.ChildRelationshipType.Name;
}

I get an error here that the object context is already closed.
How do I specify that each child object must include the ChildRelationshipType object like what I did above?

A:

If you include the library System.Data.Entity you can use an overload of the Include() method which takes a lambda expression instead of a string. You can then Select() over children with Linq expressions rather than string paths.
return DatabaseContext.Applications
     .Include(a => a.Children.Select(c => c.ChildRelationshipType));

A:

With EF Core in .NET Core you can use the keyword ThenInclude :
return DatabaseContext.Applications
 .Include(a => a.Children).ThenInclude(c => c.ChildRelationshipType);

Include childs from childrens collection :
return DatabaseContext.Applications
 .Include(a => a.Childrens).ThenInclude(cs => cs.ChildRelationshipType1)
 .Include(a => a.Childrens).ThenInclude(cs => cs.ChildRelationshipType2);

A:

I ended up doing the following and it works:
return DatabaseContext.Applications
     .Include("Children.ChildRelationshipType");

