c# - 如何将连接两个对象的 LINQ 查询语法转换为方法语法？

Question

如何以方法语法形式执行此操作:

foreach (var o in from o in orders
                  from oi in o.OrderItems
                  where oi.ProductName == "Widgets"
                  select o.OrderID)
    Console.WriteLine("{0}", o);

尝试过但不起作用:

foreach (var o in orders
    .SelectMany(o => o.OrderItems, (o, oi) => new {<<idk what to put here>> })
    .Where(oi => oi.ProductName == "Widget"))
{
    Console.WriteLine("WIDGET: {0}", o.OrderID);
}

最后我使用了这段代码，它成功了!

foreach (var o in orders
    .SelectMany(o => o.OrderItems, (o, oi) => new { o.OrderID, oi.ProductName })
    .Where(oi => oi.ProductName == "Widgets"))
{
    Console.WriteLine("{0}", o.OrderID);
}

Answer 1

方法语法如下:

orders.Where(o=>o.OrderItems.Any(oi=>oi.ProductName == "Widgets")).Select(o=>o.OrderID)