Linq加入iquery，如何使用defaultifempty [英] Linq join iquery, how to use defaultifempty

问题描述

我编写了一个 linq 连接查询，如果其中一个为空，我想获取这些值...

I have written a linq join query and I would like to take the values, if one of them are empty...

代码:

var Details = 

UnitOfWork.FlightDetails
          .Query()
          .Join
          (
              PassengersDetails,
              x => x.Flightno,
              y => y.FlightNo,
              (x, y) => new
              {
                  y.PassengerId,
                  y.classType,
                  x.Flightno,
                  x.FlightName,
              }
          );

我想使用类似......

I would like to use something like..

"Above query".DefaultIfEmpty
(
    new 
    {
        y.PassengerId,
        y.classType,
        string.Empty,
        string.Empty
    }
);

FlightDetails 是类上的 Idatarepository 类型，PassengerDetails 是 IQueryable 局部变量结果.如何获得 PassengerId 和 Classtype 的结果，而 flightno 和 flightname 不包含在整体结果中?

FlightDetails is Idatarepository type on a class and PassengerDetails is IQueryable local variable result. How can I get result with PassengerId and Classtype without flightno and flightname included in the overall results?

推荐答案

你基本上想要做一个左外连接.您当前使用 DefaultIfEmpty 方法的方式是，如果整个列表为空，则您提供一个默认条目.

You basically want to do a left outer join. The way you currently are using the DefaultIfEmpty method is that if the entire list is empty you provide a single default entry.

您应该加入 PassengerDetails 并为每个乘客详细信息列表调用默认值(如果为空).这相当于左外连接，它有点像这样:

You should join with PassengerDetails and for each passenger details list call the default if empty. This is the equivalent of a left outer join and it goes a little something like this:

var data = from fd in FlightDetails
           join pd in PassengersDetails on fd.Flightno equals pd.FlightNo into joinedT
           from pd in joinedT.DefaultIfEmpty()
           select new {
                         nr = fd.Flightno,
                         name = fd.FlightName,
                         passengerId = pd == null ? String.Empty : pd.PassengerId,
                         passengerType = pd == null ? String.Empty : pd.PassengerType
                       }

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