Include navigation property of navigation property in EF5/6 - entity-framework

Question

Here is my existing code, which fetches a user and gets his groups.
User user = new FetchUserByUsernameServiceCommand(Username, Context).Execute();
var groupList = user.JoinedGroups.ToList<Group>();
return groupList;
Each Group has a navigation property Image which has an ImageUrl.
I would like to Include the Image of each Group in the groupList, but Include is not available on the Lis<Group> groupList because it is not attached to a Context.
How can I include the Image navigation property for each Group?

Answer 1

You can either extend your command class and constructor to accept expressions for the navigation properties to include:
private string _userName;
private MyContext _context;
private Expression<Func<User, object>>[] _includes;
public FetchUserByUsernameServiceCommand(string userName,
MyContext context, params Expression<Func<User, object>>[] includes)
{
_userName = userName;
_context = context;
_includes = includes;
}
public User Execute()
{
IQueryable<User> query = _context.Users;
if (_includes != null)
{
foreach (var include in _includes)
query = query.Include(include);
}
return query.SingleOrDefault(u => u.UserName);
}
You would call this like so:
User user = new FetchUserByUsernameServiceCommand(
Username, Context, u => u.JoinedGroups.Select(g => g.Image))
.Execute();
var groupList = user.JoinedGroups.ToList();
return groupList;
Or you can use explicit loading:
User user = new FetchUserByUsernameServiceCommand(
Username, Context)
.Execute();
var groupList = Context.Entry(user).Collection(u => u.JoinedGroups).Query()
.Include(g => g.Image)
.ToList();
return groupList;
Note that only the first option is eager loading in the sense that user plus groups plus images are loaded together in a single database request. The second option (explicit loading) will run two database queries - the first one that only loads the User object in the command executor and the second one that loads groups plus images for that user.