c# - Entity Framework Many to many through containing object

Question

I was curious if it is possible to map an intermediate table through a containing object.

public class Subscriber : IEntity
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    private ChannelList _subscribedList { get; set; }
    public int NumSubscribedChannels { get { return _subscribedList.Count(); } }
}

public class HelpChannel : IEntity
{
    [Key]
    public int Id { get; set; }
    public string name { get; set; }
    public string category { get; set; }
    public int group { get; set; }
}

I need to have a subscriber table, channel table and an intermediate table to link a subscriber to his/her channels.

Is it possible to map the list that is within the ChannelList object to the Subscriber Model?

I figured that's probably not possible and that I would need to just have a private List for EF to map. But I wasn't sure if EF will do that for private variables. Will it?

I'm hoping that is does because if it has to be public to maintain the encapsulation.

Answer 1

You can map private properties in EF code-first. Here is a nice description how to do it. In your case it is about the mapping of Subscriber._subscribedList. What you can't do is this (in the context's override of OnModelCreating):

modelBuilder.Entity<Subscriber>().HasMany(x => x._subscribedList);

It won't compile, because _subscribedList is private.

What you can do is create a nested mapping class in Subscriber:

public class Subscriber : IEntity
{
    ...
    private ICollection<HelpChannel> _subscribedList { get; set; } // ICollection!

    public class SubscriberMapper : EntityTypeConfiguration<Subscriber>
    {
        public SubscriberMapper()
        {
            HasMany(s => s._subscribedList);
        }
    }
}

and in OnModelCreating:

modelBuilder.Configurations.Add(new Subscriber.SubscriberMapping());

You may want to make _subscribedList protected virtual, to allow lazy loading. But it is even possible to do eager loading with Include:

context.Subscribers.Include("_subscribedList");