Entity Framework Core (EF 7) many-to-many results always null - entity-framework-core

Question

I have followed the instructions for the workaround for many-to-many described in Issue #1368 and the Docs Here... but when I try to navigate, it always returns null.
My Models:
public class Organization
{
public Guid OrganizationID { get; set; }
//...
public ICollection<OrganizationSubscriptionPlan> OrganizationSubscriptionPlans { get; set; }
}
public class SubscriptionPlan
{
public int SubscriptionPlanID { get; set; }
//...
public ICollection<OrganizationSubscriptionPlan> OrganizationSubscriptionPlans { get; set; }
public class OrganizationSubscriptionPlan
{
[ForeignKey("Organization")]
public Guid OrganizationID { get; set; }
public Organization Organization { get; set; }
[ForeignKey("SubscriptionPlan")]
public int SubscriptionPlanID { get; set; }
public SubscriptionPlan SubscriptionPlan { get; set; }
}
ApplicationDbContext:
protected override void OnModelCreating(ModelBuilder builder)
{
base.OnModelCreating(builder);
builder.Entity<OrganizationSubscriptionPlan>().HasKey(x => new { x.OrganizationID, x.SubscriptionPlanID });
builder.Entity<OrganizationSubscriptionPlan>().HasOne(x => x.Organization).WithMany(x => x.OrganizationSubscriptionPlans).HasForeignKey(x => x.OrganizationID);
builder.Entity<OrganizationSubscriptionPlan>().HasOne(x => x.SubscriptionPlan).WithMany(x => x.OrganizationSubscriptionPlans).HasForeignKey(x => x.SubscriptionPlanID);
}
And my Query:
var organizations = _context.Organizations
.Include(o => o.OrganizationSubscriptionPlans);
foreach (var organization in organizations)
{
//....
var subscriptions = organization.OrganizationSubscriptionPlans
.Select(s => s.SubscriptionPlan);
// ^^^^^^^^^^^ why is subscriptions always null?
}
The "organizations" query returns the results as expected, including the list of OrganizationSubscriptionPlans within each one, but when I try to navigate to them in the foreach loop the "subscriptions" query returns null every time. What am I doing wrong?

Answer 1

Turns out it's a Lazy Loading issue. You have to "Include" the joining entity and then "ThenInclude" the other entity.
var organizations = _context.Organizations
.Include(o => o.OrganizationSubscriptionPlans)
.ThenInclude(s => s.SubscriptionPlan);

Answer 2

ForeignKey attr is to decorate reference properties to indicate them what primitive property hold the FK value.
public class OrganizationSubscriptionPlan
{
public Guid OrganizationID { get; set; }
[ForeignKey("OrganizationID")]
public Organization Organization { get; set; }
public int SubscriptionPlanID { get; set; }
[ForeignKey("SubscriptionPlanID")]
public SubscriptionPlan SubscriptionPlan { get; set; }
}