Entity Framework Navigation Properties Are Null - entity-framework

Question

I am having a problem where my Entity Framework navigation properties are null. My two models are Order and OrderLine:
class Order
{
public string CustomerId { get; set; }
public string OrderNumber { get; set; }
public ICollection<OrderLine> Lines { get; set; }
}
class OrderLine
{
public int LineNumber { get; set; }
public string OrderNumber { get; set; }
public string ProductId { get; set; }
public int Quantity { get; set; }
public Order Order { get; set; }
}
My Context class looks like this
class MyContext : DbContext
{
public DbSet<Order> Orders { get; set; }
public DbSet<OrderLine> OrderLines { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Order>()
.HasKey(p => p.OrderNumber);
modelBuilder.Entity<OrderLine>()
.HasKey(p => new { p.OrderNumber, p.LineNumber });
modelBuilder.Entity<OrderLine>()
.HasRequired(p => p.Order)
.WithMany(p => p.Lines)
.HasForeignKey(p => p.OrderNumber);
}
}
When I run the following code, my orders load (the message box shows the correct count), but the Order.Lines collection is null.
List<Order> orders = (from o in context.Orders select o).ToList();
// This message box shows the correct number of orders
MessageBox.Show(orders.Count.ToString());
// This line crashes because orders[0].Lines is null. There are lines in the database that should be joining to orders[0]
MessageBox.Show(orders[0].Lines.Count.ToString());
I've looked at a lot of examples, and I can't figure out what I'm doing incorrectly.

Answer 1

You need to declare the navigation properties as virtual in order to be lazy loaded:
public class Order
{
//...
public virtual ICollection<OrderLine> Lines { get; set; }
}
public class OrderLine
{
//...
public virtual Order Order { get; set; }
}
For more info check this link to see all the requirements you need to follow.