使用LINQ在列表中过滤列表

Question

I have the following classes:

class Order
{
    public string AccountNumber;
    public string AccountName;
    public List<OrderLine> OrderLines = new List<OrderLine>();
    public DateTime StartDate;
    public DateTime EndDate;       
}

class OrderLine
{
     public string Description;
     public string ProductCode;
     public double Duration;
     public int Quantity;
}

What would be the LINQ code to get the list of Order objects based upon the following conditions?

1. [Order] AccountNumber is equal to "1234"
2. [OrderLine] Quantity greater than 10

Answer 1

Assuming you want all records that match both conditions (for any satisfactory OrderLine , otherwise change to All() ):

public static void IEnumerable<Order> GetQualifying(this IEnumerable<Order> orders, string accountNo, int minQty) {
    return orders.Where(o =>
        o.AccountNumber == accountNo
        && o.OrderLines.Any(ol => ol.Quantity >= minQty);
}

Be careful not to get an off-by-one error as I have interpreted "minimum quantity" literally.

Also, the this syntax is great for writing extension methods , which allow you to invoke like this:

Order[] orders = //stuff;
Order[] qualifiedOrders = orders.GetQualifying("1234", 9).ToArray();

Note that I recommend using as ToArray() as soon as you can no longer benefit from lazy evaluation , otherwise doing subsequent operations on raw IEnumerable<> will cause reevaluation (read: enumerating the collection again).

Answer 2

You could go with:

list.Where(x => x.AccountNumber == "12345" && x.OrderLines.Any(o => o.Quantity > 10));

or:

list.Where(x => x.AccountNumber == "12345" && x.OrderLines.All(o => o.Quantity > 10));

depending on whether you want to retrieve all objects that have an AccountNumber of 12345 and any OrderLine quantity greater than 10 or if all OrderLine quantity is greater than 10