MVC Entity Framework Partial Class access DB for property value

I am using Entity Framework mapped to my database. I have a Basket model which can have many BasketItem models, and I have Promotions and Coupons models. This is for eCommerce checkout functionality and I just don't understand how this will work, here goes:

Because my BasketItems have a foreign key relationship to the Basket if I want to sum up the Subtotal for my basket items in a partial class, I can do this:

        public decimal Subtotal {
        get {
            return this.BasketItems.Sum(pb => pb.Subtotal);
            }
        }

This is helpful because I can use this inside a view, there's no mucking around with passing a DB context through and it's DRY, etc. etc.

Now I want to apply promotions or coupons to my Subtotal ideally I want it to look like this:

        public decimal DiscountedSubtotal {
        get { 
            decimal promotions_discount = 0;
            decimal coupons_discount = 0;
            return Subtotal - promotions_discount - coupons_discount;
            }
        }

But there is no access to Promotions or Coupons without either creating some crazy and unnecessary relationships in my database or some light hacking to get this functionality to work. I don't know what I should do to overcome this problem.

Solution 1:

        public decimal DiscountedSubtotal(DatabaseEntities db) {
        decimal promotions_discount = from p in db.Promotions
                                  select p.Amount;
        decimal coupons_discount = from c in db.Coupons
                               select c.Amount;
        return Subtotal - promotions_discount - coupons_discount;
        }

I don't want to use this in my View pages, plus I have to send through my context every time I want to use it.

Solution 2: (untested)

    public List<Promotion> Promotions { get; set; }
    public List<Coupon> Coupons { get; set; }

    public Basket()
        : base() {
            DatabaseEntities db = new DatabaseEntities();
            Promotions = db.Promotions.ToList();
            Coupons = db.Coupons.ToList();
    }

A bit of light hacking could provide me with references to promotions and coupons but i've had problems with creating new contexts before and I don't know if there is a better way to get me to the DiscountedSubtotal property I would ideally like.

So to sum up my question, I would like to know the best way to get a DiscountedSubtotal property.

Many thanks and apologies for such a long read :)