How to eager load child entities using repository pattern

Question

I have an entity named Tour which can have many Agents. I am able to add agents, but I cannot remove them.

// _repo is injected....
var tour = _repo.GetById(tourId);
tour.AddAgent(new Agent(tour.TourId));

When I attempt to call the Tour.RemoveAgent() method nothing is actually removed. I set a breakpoint inside the Tour.RemoveAgent() method I see that the _agents property has a count of 0.

tour.RemoveAgent(agentId); // This doesn't work because _agents is empty

Do I have to do something special for EF to populate the _agents property when I retrieve the Tour from my repository?

UPDATE: PROBLEM SOLVED (thanks to Paul's answer)

I decided to just create a Repository unique to each aggregate, that way it is easy to define exactly what needs to be included using the Include() function. This is an example where I inherit from the GenericRepository<T> class (which is also included at the bottom of this question).

public class TourRepository : GenericRepository<Tour>
{
    public TourRepository(IDatabaseFactory databaseFactory) : base (databaseFactory)
    {
    }

    public override Tour GetById(Guid id)
    {
        return dataContext.Tours
                .Include(x => x.Agents)
                .Single(x => x.TourId == id);
    }
}

Tour Class

public partial class Tour
{
  public Guid TourId { get; private set; }
  protected virtual List<Agent> _agents { get; set; }

  public Tour()
  {
    TourId = Guid.NewGuid();
    _agents = new List<Agent>();
  }

  public void AddAgent(Agent agent)
  {
    _agents.Add(agent);
  }

  public void RemoveAgent(Guid agentId)
  {
    _agents.RemoveAll(a => a.AgentId == agentId);
  }
}

Agent Class

public partial class Agent
{
  public Guid AgentId { get; private set; }
  public Guid TourId { get; private set; }
  public Tour Tour { get; private set; }

  public Agent(Guid tourId)
  {
    TourId = tourId;
    AgentId = Guid.NewGuid();
  }
}

OnModelCreating

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
  // AGENTS ============================
  modelBuilder.Entity<Agent>()
              .HasKey(x => x.AgentId)
              .Property(p => p.AgentId);

  modelBuilder.Entity<Agent>()
              .HasRequired(p => p.Tour)
              .WithMany(t => t.Agents);

  // TOURS =============================
  modelBuilder.Entity<Tour>()
              .HasKey(x => x.TourId)
              .Property(x => x.TourId);
}

Repository Class

public class GenericRepository<T> : IRepository<T> where T : class {
  private MyContext dataContext;
  private readonly IDbSet<T> dbset;  
  
  public GenericRepository(IDatabaseFactory databaseFactory)
  {
    DatabaseFactory = databaseFactory;
    dbset = DataContext.Set<T>();
  }

  protected IDatabaseFactory DatabaseFactory
  {
    get;
    private set;
  }

  protected MyContext DataContext
  {
    get { return dataContext ?? (dataContext = DatabaseFactory.Get()); }
  }
  
  // ... stuff removed for brevity ...
  
  public T GetById(Guid id)
  {
    return dbset.Find(id);
  }
}

Bidle

Are you using UoW as well? Have you tried eager loading to test? – Puce

You would not use the .Find method, you would _databaseContext.Tours.Include(x => x.Agent).Single(x => x.TourId == tourId) you can read more here: blogs.msdn.com/b/adonet/archive/2011/01/31/… – Puce

Answer 1

Try making protected virtual List _agents { get; set; } public

public virtual List<Agent> _agents { get; set; }

You can also eager load by doing something like this:

_databaseContext.Tours.Include(x => x.Agents).Single(x => x.TourId == tourId) 

you can read more here: http://blogs.msdn.com/b/adonet/archive/2011/01/31/using-dbcontext-in-ef-feature-ctp5-part-6-loading-related-entities.aspx

Puce

Thanks for your answer. I updated my question with my solution to the problem which makes use of your advice. – Bidle