Question

我有一个包含list属性的实体对象。我想将列表值扩展到右侧。作为LINQ的新手，我不知道该如何做到这一点。我可以强力键入一个对象，但是我必须在编译时知道计数/值，并且我想让它更具动态性。

我想要的输出类似于：

名称demo1的DEMO2 Demo3
人名1 TX TX
人名2 TX OK
人名3 TX TX OK

Main Class



public Main()
{
    List<Event> events = new List<Event>();
    events.Add(new Event()
    {
        EventDate = DateTime.Now,
        EventLocation = new Location() { State = "TX" },
        EventName = "Demo1"
    });
    events.Add(new Event()
    {
        EventDate = DateTime.Now,
        EventLocation = events[0].EventLocation,
        EventName = "Demo2"
    });
    events.Add(new Event()
    {
        EventDate = DateTime.Now,
        EventLocation = new Location() { State = "OK" },
        EventName = "Demo3"
    });

    List<Person> people = new List<Person>();

    Person person1 = new Person();
    person1.Name = "Person Name1";
    person1.Events.Add(events[0]);
    person1.Events.Add(events[1]);

    Person person2 = new Person();
    person2.Name = "Person Name2";
    person2.Events.Add(events[0]);
    person2.Events.Add(events[2]);

    Person person3 = new Person();
    person3.Name = "Person Name3";
    person3.Events.Add(events[0]);
    person3.Events.Add(events[1]);
    person3.Events.Add(events[2]);
    people.Add(person1);
    people.Add(person2);
    people.Add(person3);
}

public Main() { List<Event> events = new List<Event>(); events.Add(new Event() { EventDate = DateTime.Now, EventLocation = new Location() { State = "TX" }, EventName = "Demo1" }); events.Add(new Event() { EventDate = DateTime.Now, EventLocation = events[0].EventLocation, EventName = "Demo2" }); events.Add(new Event() { EventDate = DateTime.Now, EventLocation = new Location() { State = "OK" }, EventName = "Demo3" }); List<Person> people = new List<Person>(); Person person1 = new Person(); person1.Name = "Person Name1"; person1.Events.Add(events[0]); person1.Events.Add(events[1]); Person person2 = new Person(); person2.Name = "Person Name2"; person2.Events.Add(events[0]); person2.Events.Add(events[2]); Person person3 = new Person(); person3.Name = "Person Name3"; person3.Events.Add(events[0]); person3.Events.Add(events[1]); person3.Events.Add(events[2]); people.Add(person1); people.Add(person2); people.Add(person3); }

Answer 1

这取决于您是要在内存中还是在数据库中运行查询。在任何情况下，您都需要返回一个包含结果“动态”部分的列表，因为您无法动态生成匿名类型的成员（并且难以使用它们）。

在内存中（如示例所示），您可以编写以下查询：

// Find names of all events (for all people)
var allNames = 
  (from p in people
    from e in p.Events
    select e.EventName).Distinct();

// Find events for every person
var res = 
  from p in people
  let known = p.Events.ToDictionary(e => e.EventName)
  select new { 
    p.Name, 
    Events = allNames.Select(n => 
      known.ContainsKey(n)?known[n].EventLocation:"N/A")
  };

第一个查询获取所有事件的名称（我们稍后使用它来为每个人查找所有事件的值）。第二个查询遍历所有人。它首先创建带有事件的字典（用于在内存中快速查找），然后迭代所有事件名称并尝试在字典中找到它们（如果找不到则返回“N / A”）。

Linq使用列表属性“报告”问题

1 个答案: