.net - 通过 LINQ 选择十进制值

Question

我正在尝试在 MVC3 项目中使用 LINQ 获取十进制值。

我如何获得它？看起来很简单的问题，但我无法得到单个十进制值而不是 Product.aWeekPrice 列表。

如何获得特定的threeDayPrice？获得 threeDayPrice 后，它将在 if 条件中用于给出不同的条件，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;
        }        
    }

Answer 1

如果您的查询总是只返回一个值，请使用 .Single()将其作为 decimal 而不是小数集合。

    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();

如果查询可能返回多于一个或零个元素，请使用 First()/FirstOrDefault()而是。