具有多个集合的 LINQ 嵌套分组

Question

我目前正在努力在我的对象集合上组装 LINQ 查询： 人物， 汽车

每个人都可以拥有多辆车。

我想选择所有人和所有组拥有此人拥有的所有汽车。到目前为止，我写的查询是：

from c in persons,d in cars 
    where c.id = d.ownerID 
    group by c.Firstname into MG = tolist() 

但它只返回有车的人。如果一个人没有车，他就不在名单上。我无法用正确的逻辑来弥补。

Answer 1

尝试：

List<person> plist = new List<person>();
        plist.Add(new person(1, "a"));
        plist.Add(new person(2, "b"));
        plist.Add(new person(3, "c"));
        plist.Add(new person(4, "d"));
        List<cars> clist = new List<cars>();
        clist.Add(new cars(1, "c1"));
        clist.Add(new cars(1, "c2"));
        clist.Add(new cars(1, "c5"));
        clist.Add(new cars(2, "c1"));
        clist.Add(new cars(3, "c1"));
        clist.Add(new cars(3, "c5"));
        clist.Add(new cars(3, "c3"));
        clist.Add(new cars(3, "c2"));
        clist.Add(new cars(4, "c2"));
        clist.Add(new cars(4, "c5"));

        var result = from p in plist
                join c in clist on p.id equals c.ownerID into k
                from s in k.DefaultIfEmpty()
                select new { p.firstName , carName = (s == null ? String.Empty :s.name)};
string sss = "";
 foreach (var v in result)
 {
      sss+= ( v.firstName + " : " + v.carName +  " >> "+"n");
 }
 textBox1.Text = sss;

和类是：

class person
{
    public int id;
    public string firstName;
    public person(int id1, string name)
    {
        id = id1;
        firstName = name;
    }
}
class cars
{
    public int ownerID;
    public string name;
   public cars(int id,string name1)
    {
        ownerID = id;
        name = name1;
    }
}