Many to one configuration using EF 4.1 code first -

i have following classes:

public class cartitem {     public long id { get; set; }     public int quantity { get; set; }     public product product { get; set; } }  public class product    {     public long id { get; set; }     public string title { get; set; }     public decimal price { get; set; } } 

i have following configuration:

modelbuilder.entity<cartitem>().hasrequired(x => x.product).withmany().map(x => x.mapkey("productid")); 

i trying ensure whenever retrieve cartitem database there join on product table can access product properties not other way around.

i want able do:

string title = cartitem.product.title 

using configuration have gives me object reference not set instance of object exception.

short answer: solve problem, make product property virtual.

in-depth:

first, don't need join this. ef works fine lazy loading (you need virtual modifier)

second, can fetch product eagerly, using include extension method. example:

var cartitem = context.cartitems.include(x => x.product)                       .where(/*some condition*/).tolist(); 

...but can't configure default behavior (nor idea usually)

third, many-to-one relationship, not one-to-one (a product has many related cartitems)