我有两个称为CountryMobility的对象，我相信我需要将其与完整的外部联接结合在一起。我如何使用linq做到这一点？

public class CountryMobility
{
    public string countryCode { get; set; }
    public int inbound { get; set; }
    public int outbound { get; set; }
}

我想像这样组合其中两个对象：

inboundStudents:
countryCode | inbound | outbound
         EG |    2    |     0
         CA |    3    |     0
         CH |    5    |     0

outboundStudents:
countryCode | inbound | outbound
         PE |    0    |     1
         CA |    0    |     4
         CH |    0    |     5


                      -
                      -
                      -
                      -
                      V

combinedStudents:
countryCode | inbound | outbound
         PE |    0    |     1
         CA |    3    |     4
         CH |    5    |     5
         EG |    2    |     0

我尝试了以下linq语句，但无法找出正确的语法。我目前在两个语句中都在temp.DefaultIfEmpty（new {first.ID，inbound =
0，outbound = 0}）附近收到语法错误。

var leftOuterJoin = 
    from first in inboundActivities
    join last in outboundActivities
    on first.countryCode equals last.countryCode
    into temp
    from last in temp.DefaultIfEmpty
    (new { first.countryCode, inbound = 0, outbound=0 })
    select new CountryMobility
    {
        countryCode = first.countryCode,
        inbound = first.inbound,
        outbound = last.outbound,
    };
var rightOuterJoin = 
    from last in outboundActivities
    join first in inboundActivities
    on last.countryCode equals first.countryCode
    into temp
    from first in temp.DefaultIfEmpty
    (new { last.countryCode, inbound = 0, outbound = 0 })
    select new CountryMobility
    {
        countryCode = last.countryCode,
        inbound = first.inbound,
        outbound = last.outbound,
    };

var fullOuterJoin = leftOuterJoin.Union(rightOuterJoin);