Question

I’m using Entity Framework Code First. The class i’m trying to create contains two collections (of the same type). I’m having problem recovering my respective collections.

My classes look like this:

public class Destination
{   
    public int DestinationId { get; set; } 
    public string Name { get; set; } 
    public List<Lodging> Lodgings { get; set; }           
    public List<Lodging> Lodgings2 { get; set; }
}
public class Lodging
{  
    public int LodgingId { get; set; } 
    public string Name { get; set; } 
    public Destination Destination { get; set; }
}

I created a new Destination, then I reopened (closed & opened) the database connection. When I retrieve the destination, my collections (dest.Lodgings and dest.Lodgings2) are null. How do I restore the respective collections? If my class only has one collection of a particular type, I could do the following:

var lodgings = context.Lodgings.Where(l => l.Destination.DestinationId == destId).ToList();

I can see that the relationships are maintained in the database schema (Destination_DestinationId1 and Destination_DestinationId2) but I don’t seem to be able to get to them.
Any suggestion would be appreciated.

Answer 1

In addition to using Include (as you’ve discovered) (which loads the related data from the db at the same time the destination is retrieved) you can also retreive the lodgings after the fact. So if you query for the destination and then you want the lodgings, that’s possible. One way is called explicit loading where you will use a Load method. The other is with lazy loading, which requires that your classes be set up a particular way and just the mere mention of the Lodgings property will trigger the call to the database to retrieve them.

there’s a great blog post on the Ef team blog about the various ways to load related data with DbContext : http://blogs.msdn.com/b/adonet/archive/2011/01/31/using-dbcontext-in-ef-feature-ctp5-part-6-loading-related-entities.aspx

hth

Julie