.net - 通过LINQ选择十进制值

我试图在MVC3项目中使用LINQ获取十进制值。

我如何得到它？它看起来很简单，但我无法获得一个十进制值而不是Product.aWeekPrice列表。

如何获得特定的ThreeDayPrice？在获得threeDayPrice之后，将在if条件中给出不同的条件，如下面的代码所示：

    public decimal GetTotal(decimal price)
    {
        // Multiply product price by count of that album to get
        // the current price for each of those product in the cart
        // sum all product price totals to get the cart total

        //In select part, I have got error, 'cannot convert type
        //'System.Linq.IQueryable<decimal>' to 'decimal'

        decimal threeDayPrice = (from cartItems in db.Cart
                              where cartItems.cartId == ShoppingCartId
                                 select (decimal)cartItems.Product.threeDayPrice);

        decimal aWeekPrice = (from cartItems in db.Cart
                                 where cartItems.cartId == ShoppingCartId
                                 select (decimal)cartItems.Product.aWeekPrice);

        if (price == threeDayPrice)
        {
            decimal? total = (from cartItems in db.Cart
                              where cartItems.cartId == ShoppingCartId
                              select (int?)cartItems.count * cartItems.Product.threeDayPrice).Sum();
            return total ?? decimal.Zero;
        }

        else if (price == aWeekPrice)
        {
            decimal? total = (from cartItems in db.Cart
                              where cartItems.cartId == ShoppingCartId
                              select (int?)cartItems.count * cartItems.Product.aWeekPrice).Sum();
            return total ?? decimal.Zero;
        }
    }

最佳答案

如果查询始终只返回一个值，请使用.Single()将其作为decimal而不是小数的集合。

    decimal threeDayPrice = (from cartItems in db.Cart
                          where cartItems.cartId == ShoppingCartId
                             select (decimal)cartItems.Product.threeDayPrice).Single();

    decimal aWeekPrice = (from cartItems in db.Cart
                             where cartItems.cartId == ShoppingCartId
                             select (decimal)cartItems.Product.aWeekPrice).Single();

如果查询可能返回更多，则使用First() / FirstOrDefault()代替一个或零个元素。