Session<T> with/without Repository

WithoutRepo.cs

public interface IPersonService
{
    PersonViewModel GetPersonViewModel(int id);
}

public class PersonService : IPersonService
{
    ISession _session;
    public PersonService(ISession session)
    {
        _session = session;
    }

    public PersonViewModel GetPersonViewModel(int id)
    {
        var person = _session.Single<Person>(x=>x.Id == id);
        return new PersonViewModel
        {
            Id = person.Id,
            FirstName = person.FirstName,
            LastName = person.LastName
        };
    }
}

WithRepo.cs

public interface IPersonRespository
{
    Person GetPersonById(int id);
}

public class PersonRepository : IPersonRespository
{
    ISession _session;
    public PersonRepository(ISession session)
    {
        _session = session;
    }

    Person GetPersonById(int id)
    {
        return _session.Single<Person>(x => x.Id == id);
    }
}

public interface IPersonService
{
    PersonViewModel GetPersonViewModel(int id);
}

public class PersonService : IPersonService
{
    IPersonRespository _personRepository;
    public PersonService(IPersonRespository personRepository)
    {
        _personRepository = personRepository;
    }

    public PersonViewModel GetPersonViewModel(int id)
    {
        var person = _personRepository.GetPersonById(id);
        return new PersonViewModel
        {
            Id = person.Id,
            FirstName = person.FirstName,
            LastName = person.LastName
        }
    }
}