linq加入1对多人获得第一记录

// 假设有两个实体类：Person和Order
public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Order
{
    public int Id { get; set; }
    public int PersonId { get; set; }
    public string Product { get; set; }
}

// 假设有两个数据集：persons和orders
List<Person> persons = new List<Person>
{
    new Person { Id = 1, Name = "Alice" },
    new Person { Id = 2, Name = "Bob" },
    new Person { Id = 3, Name = "Charlie" }
};

List<Order> orders = new List<Order>
{
    new Order { Id = 1, PersonId = 1, Product = "Product A" },
    new Order { Id = 2, PersonId = 1, Product = "Product B" },
    new Order { Id = 3, PersonId = 2, Product = "Product C" },
    new Order { Id = 4, PersonId = 2, Product = "Product D" },
    new Order { Id = 5, PersonId = 3, Product = "Product E" }
};

// 使用LINQ查询获取每个人的第一条订单记录
var result = from person in persons
             join order in orders on person.Id equals order.PersonId into personOrders
             select new
             {
                 PersonName = person.Name,
                 FirstOrder = personOrders.FirstOrDefault()
             };

// 输出结果
foreach (var item in result)
{
    Console.WriteLine($"Person: {item.PersonName}, First Order: {item.FirstOrder?.Product ?? "No order"}");
}