.net LINQ 完全外部联接

我有一份身份证和名字的 list ，还有一份身份证和姓氏的 list .有些人没有名字，有些人没有姓氏；我想在这两个列表上做一个完整的外部连接.

因此，下面列出了以下列表:

ID  FirstName
--  ---------
 1  John
 2  Sue

ID  LastName
--  --------
 1  Doe
 3  Smith

应产生:

ID  FirstName  LastName
--  ---------  --------
 1  John       Doe
 2  Sue
 3             Smith

我是LINQ的新手(如果我是跛脚的话，请原谅我)，我已经找到了很多关于"LINQ外部联接"的解决方案，它们看起来非常相似，但实际上似乎是左外部联接.

到目前为止，我的try 是这样的:

private void OuterJoinTest()
{
    List<FirstName> firstNames = new List<FirstName>();
    firstNames.Add(new FirstName { ID = 1, Name = "John" });
    firstNames.Add(new FirstName { ID = 2, Name = "Sue" });

    List<LastName> lastNames = new List<LastName>();
    lastNames.Add(new LastName { ID = 1, Name = "Doe" });
    lastNames.Add(new LastName { ID = 3, Name = "Smith" });

    var outerJoin = from first in firstNames
        join last in lastNames
        on first.ID equals last.ID
        into temp
        from last in temp.DefaultIfEmpty()
        select new
        {
            id = first != null ? first.ID : last.ID,
            firstname = first != null ? first.Name : string.Empty,
            surname = last != null ? last.Name : string.Empty
        };
    }
}

public class FirstName
{
    public int ID;

    public string Name;
}

public class LastName
{
    public int ID;

    public string Name;
}

但这会返回:

ID  FirstName  LastName
--  ---------  --------
 1  John       Doe
 2  Sue

我做错了什么？