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?

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));

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);

I ended up doing the following and it works:

return DatabaseContext.Applications
     .Include("Children.ChildRelationshipType");

A good example of using the Generic Repository pattern and implementing a generic solution for this might look something like this.

public IList<TEntity> Get<TParamater>(IList<Expression<Func<TEntity, TParamater>>> includeProperties)

{
    
    foreach (var include in includeProperties)
     {

        query = query.Include(include);
     }
        
        return query.ToList();
}