针对子列表的 C# Linq 查询

Question

I have a class structure as below whereby I have a list of OrderItems and each item has a list of Discounts

public class Order
{
    public IList<OrderItem> OrderItems = new List<OrderItem>();
}

public class OrderItem
{
    public IList<Discount> Discounts = new List<Discount>();
}

public class Discount
{
    public string Desc { get; set; }
    public decimal Amount { get; set; }
    public bool IsActive { get; set; }
}

If I want to get a list of all discounts with an IsActive flag of true, how would I do this in a Linq query?

Currently this is what I have but it is very ugly with 2 foreach statements that need to be removed.

IList<Discount> activeDiscounts = new List<Discount>();
        foreach (OrderItem item in order.OrderItems)
        {
            var aDiscounts = from discount in item.Discounts.AsEnumerable()
                    where discount.IsActive == true
                    select discount;
            foreach (Discount discount in aDiscounts)
            {
                activeDiscounts.Add(discount);
            }
        }

Answer 1

这是一行 linq 语句：

order.OrderItems.SelectMany(item => item.Discounts.Where(discount => discount.IsActive));