Question

我在C＃中有多个条件的LINQ Joining语句。

var possibleSegments = 
    from epl in eventPotentialLegs
    join sd in segmentDurations on 
        new { 
            epl.ITARequestID, 
            epl.ITASliceNumber, 
            epl.DepartAirportAfter, 
            epl.AirportId_Origin, 
            epl.AirportId_Destination 
        } 
        equals 
        new { 
            sd.ITARequestId, 
            sd.SliceIndex, 
            sd.OriginAirport, 
            sd.DestinationAirport 
        }
    where
        epl.DepartAirportAfter > sd.UTCDepartureTime 
        and 
        epl.ArriveAirportBy > sd.UTCArrivalTime
    select new PossibleSegments{ ArrivalTime = sd.arrivalTime };

加入无效。我做错了什么？

Answer 1

AFAIK你只能这样加入：

var query = from obj_i in set1
join obj_j in set2 on 
    new { 
      JoinProperty1 = obj_i.SomeField1,
      JoinProperty2 = obj_i.SomeField2,
      JoinProperty3 = obj_i.SomeField3,
      JoinProperty4 = obj_i.SomeField4
    } 
    equals 
    new { 
      JoinProperty1 = obj_j.SomeOtherField1,
      JoinProperty2 = obj_j.SomeOtherField2,
      JoinProperty3 = obj_j.SomeOtherField3,
      JoinProperty4 = obj_j.SomeOtherField4
    }

主要要求是：您加入的匿名对象中的属性名称，类型和顺序必须匹配。

您不能在联接中使用ANDs OR等。只是object1等于object2。

这个LinqPad示例中更高级的内容：

class c1 
    {
    public int someIntField;
    public string someStringField;
    }

class c2 
    {
    public Int64 someInt64Property {get;set;}
    private object someField;
    public string someStringFunction(){return someField.ToString();}
    }

void Main()
{
    var set1 = new List<c1>();
    var set2 = new List<c2>();

    var query = from obj_i in set1
    join obj_j in set2 on 
        new { 
                JoinProperty1 = (Int64) obj_i.someIntField,
                JoinProperty2 = obj_i.someStringField
            } 
        equals 
        new { 
                JoinProperty1 = obj_j.someInt64Property,
                JoinProperty2 = obj_j.someStringFunction()
            }
    select new {obj1 = obj_i, obj2 = obj_j};
}

寻址名称和属性顺序很简单，寻址类型可以通过转换/转换/解析/调用方法等来实现。这可能并不总是适用于LINQ to EF或SQL或NHibernate，大多数方法调用肯定不起作用，在运行时会失败，所以YMMV。这是因为它们被复制到匿名对象中的公共只读属性，因此只要表达式生成正确类型的值连接属性 - 您应该没问题。

Answer 2

您的and应该是&&条款中的where。

where epl.DepartAirportAfter >  sd.UTCDepartureTime 
and epl.ArriveAirportBy > sd.UTCArrivalTime

应该是

where epl.DepartAirportAfter >  sd.UTCDepartureTime 
&& epl.ArriveAirportBy > sd.UTCArrivalTime

Answer 3

如果您不需要相等的对象条件，请使用交叉连接序列：

var query = from obj1 in set1
from obj2 in set2
where obj1.key1 == obj2.key2 && obj1.key3.contains(obj2.key5) [...conditions...]

LINQ以多种条件加入C＃

3 个答案: