Where命令，8

Question

我可以在不使用where命令的情况下获得以下提要，当我将where命令放入其中时，我无法使它工作。

1231是routeId可以成为的值，也是routeId在获得select命令时的值。

有什么原因导致失败吗？

还曾尝试：

where s.Element("routeId").Value.Contains("1231") 

和

where s.Attribute("routeId").Value == "1231"

和

where s.Element("routeId").Value == ("1231")

当前代码：

var routeNames = (from n in doc.Descendants(ns + "Service") 
                    select new RootContainer
                    {
                        Service = (from s in n.Element(ns + "routes").Elements(ns + "Route")
                        // where (n.Elements(ns + "timetables").Elements(ns + "Timetable").Elements(ns + "daysOfWeek").ToString() == "Sundays and Public Holidays from 14 September")

                        where s.Element("routeId").Value == "1231"
                        select new Services
                        {
                            RouteName = s.Element(ns + "routeName").Value, RouteId = s.Element(ns + "routeId").Value,
                            // Routes = s.Element(ns + "routeId").Attribute("1231").Value


                            //  TimetableName = s.Element(ns + "timetables").Element(ns + "Timetable").Element(ns + "daysOfWeek").Value,


                        }).ToList()

                    }).First();

这是完整的XML。

我的目标是得到每一个时间表:星期一到星期五，星期六和星期日.或大意的文字，因为这改变了这个提要中包含的内容。

   <Service z:Id="i1" xmlns="http://schemas.datacontract.org/2004/07/BusExpress.ClassLibrary"    xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/">

 <routes>
  <Route z:Id="i4">
     <routeId>1231</routeId>
  <routeMap>
    <RouteMap z:Id="i6">

      <routeLineCenterLat>50.82754</routeLineCenterLat>
      <routeLineCenterLng>-0.166640326</routeLineCenterLng>
      <routeLineColour>#0000FF</routeLineColour>
      <routeLineFilename i:nil="true" />
      <routeLineInitialZoom>12</routeLineInitialZoom>
      <routeMapId>379</routeMapId>
      <routeMapName>1 Whitehawk - Mile Oak</routeMapName>
     </RouteMap>
  </routeMap>
  <routeName>1 Whitehawk - Mile Oak</routeName>
  <route_stop />
  <route_stop_stop />
  <route_stop_timetable_stop />
  <service z:Ref="i1" />
   <timetables>
    <Timetable z:Id="i8">
      <dateAdded>2013-08-27T13:22:26.703</dateAdded>
      <daysOfWeek>Sundays and Public Holidays</daysOfWeek>
      <isLive>false</isLive>
      <relativePosition>2</relativePosition>
      <route z:Ref="i4" />
      <route_stop_timetable_stop />
      <timetableDescription>Whitehawk - County Hospital - Brighton - Hove - Portslade - Mile Oak</timetableDescription>
      <timetableFilename>timetable_635132065412586254_0.xml</timetableFilename>
      <timetableId>10121</timetableId>
      <timetableName>1 1A Whitehawk - Mile Oak</timetableName>
      <timetable_stop />
      <validDates i:nil="true" />
    </Timetable>
    <Timetable z:Id="i10">
       <dateAdded>2014-03-26T13:09:06.233</dateAdded>
      <daysOfWeek>Mondays to Fridays</daysOfWeek>
      <isLive>false</isLive>
      <relativePosition>0</relativePosition>
      <route z:Ref="i4" />
      <routeReference xmlns:a="http://schemas.datacontract.org/2004/07/System.Data.Objects.DataClasses">
        <a:EntityKey z:Ref="i5" xmlns:b="http://schemas.datacontract.org/2004/07/System.Data" />
      </routeReference>
      <route_stop_timetable_stop />
      <timetableDescription>Whitehawk - County Hospital - Brighton - Hove - Portslade - Mile Oak</timetableDescription>
      <timetableFilename>timetable_635314361366540988_0.xml</timetableFilename>
      <timetableId>10315</timetableId>
      <timetableName>1 1A Whitehawk - Mile Oak</timetableName>
      <timetable_stop />
      <validDates />
    </Timetable>
    <Timetable z:Id="i12">
      <dateAdded>2014-03-26T13:09:53.017</dateAdded>
      <daysOfWeek>Saturdays</daysOfWeek>
      <isLive>false</isLive>
      <relativePosition>1</relativePosition>
      <route z:Ref="i4" />
      <routeReference xmlns:a="http://schemas.datacontract.org/2004/07/System.Data.Objects.DataClasses">
        <a:EntityKey z:Ref="i5" xmlns:b="http://schemas.datacontract.org/2004/07/System.Data" />
      </routeReference>
      <route_stop_timetable_stop />
      <timetableDescription>Whitehawk - County Hospital - Brighton - Hove - Portslade - Mile Oak</timetableDescription>
      <timetableFilename>timetable_635314361868081863_0.xml</timetableFilename>
      <timetableId>10317</timetableId>
      <timetableName>1 1A Whitehawk - Mile Oak</timetableName>
      <timetable_stop />
      <validDates />
    </Timetable>
  </timetables>
  <validDestination>Mile Oak</validDestination>
</Route>
<Route z:Id="i14">

 <dateEffectiveFrom>2012-09-01T00:00:00</dateEffectiveFrom>
  <dateEffectiveTo i:nil="true" />
  <isLive>true</isLive>
  <relativePosition>0</relativePosition>
  <routeDescription i:nil="true" />
  <routeId>1235</routeId>
  <routeMap>
    <RouteMap z:Id="i16">
       <routeLineCenterLat>50.82936</routeLineCenterLat>
      <routeLineCenterLng>-0.1599884</routeLineCenterLng>
      <routeLineColour>#0000FF</routeLineColour>
      <routeLineFilename i:nil="true" />
      <routeLineInitialZoom>12</routeLineInitialZoom>
      <routeMapId>383</routeMapId>
      <routeMapName>1 Mile Oak - Whitehawk</routeMapName>
      <routeReference xmlns:a="http://schemas.datacontract.org/2004/07/System.Data.Objects.DataClasses">
        <a:EntityKey z:Ref="i15" xmlns:b="http://schemas.datacontract.org/2004/07/System.Data" />
      </routeReference>
    </RouteMap>
  </routeMap>
  <routeName>1 Mile Oak - Whitehawk</routeName>
  <route_stop />
  <route_stop_stop />
  <route_stop_timetable_stop />
  <service z:Ref="i1" />
   <timetables>
    <Timetable z:Id="i18">

      <dateAdded>2013-08-27T13:22:26.72</dateAdded>
      <daysOfWeek>Sundays and Public Holidays</daysOfWeek>
      <isLive>false</isLive>
      <relativePosition>2</relativePosition>
      <route z:Ref="i14" />
      <routeReference xmlns:a="http://schemas.datacontract.org/2004/07/System.Data.Objects.DataClasses">
        <a:EntityKey z:Ref="i15" xmlns:b="http://schemas.datacontract.org/2004/07/System.Data" />
      </routeReference>
      <route_stop_timetable_stop />
      <timetableDescription>Mile Oak - Portslade - Hove - Brighton - County Hospital - Whitehawk</timetableDescription>
      <timetableFilename>timetable_635132065412586254_1.xml</timetableFilename>
      <timetableId>10122</timetableId>
      <timetableName>1 1A Mile Oak - Whitehawk</timetableName>
      <timetable_stop />
      <validDates i:nil="true" />
    </Timetable>
    <Timetable z:Id="i20">

      <dateAdded>2014-03-26T13:09:06.297</dateAdded>
      <daysOfWeek>Mondays to Fridays</daysOfWeek>
      <isLive>false</isLive>
      <relativePosition>0</relativePosition>
      <route z:Ref="i14" />
      <routeReference xmlns:a="http://schemas.datacontract.org/2004/07/System.Data.Objects.DataClasses">
        <a:EntityKey z:Ref="i15" xmlns:b="http://schemas.datacontract.org/2004/07/System.Data" />
      </routeReference>
      <route_stop_timetable_stop />
      <timetableDescription>Mile Oak - Portslade - Hove - Brighton - County Hospital - Whitehawk</timetableDescription>
      <timetableFilename>timetable_635314361366540988_1.xml</timetableFilename>
      <timetableId>10316</timetableId>
      <timetableName>1 1A Mile Oak - Whitehawk</timetableName>
      <timetable_stop />
      <validDates />
    </Timetable>
    <Timetable z:Id="i22">

      <dateAdded>2014-03-26T13:09:53.047</dateAdded>
      <daysOfWeek>Saturdays</daysOfWeek>
      <isLive>false</isLive>
      <relativePosition>1</relativePosition>
      <route z:Ref="i14" />
      <routeReference xmlns:a="http://schemas.datacontract.org/2004/07/System.Data.Objects.DataClasses">
        <a:EntityKey z:Ref="i15" xmlns:b="http://schemas.datacontract.org/2004/07/System.Data" />
      </routeReference>
      <route_stop_timetable_stop />
          <timetableDescription>Mile Oak - Portslade - Hove - Brighton - County Hospital - Whitehawk</timetableDescription>
      <timetableFilename>timetable_635314361868081863_1.xml</timetableFilename>
      <timetableId>10318</timetableId>
      <timetableName>1 1A Mile Oak - Whitehawk</timetableName>
      <timetable_stop />
      <validDates />
    </Timetable>
  </timetables>
  <validDestination>Whitehawk, Brighton Stn</validDestination>
   </Route>
  </routes>
   <serviceAbbreviatedName />
  <serviceDescription>Whitehawk - County Hospital - City Centre - Hove - Portslade - Mile Oak</serviceDescription>

  <serviceId>1149</serviceId>
  <serviceName>1</serviceName>

  <serviceText>Whitehawk - Mile Oak</serviceText>

</Service>

Answer 1

除了@KooKiz已经解释了如何安全检查routeId元素值之外，您的查询还遗漏了使用所需的XNamespace for routeId元素：

where (string)s.Element(ns+"routeId") == "1231"

Answer 2

查询失败，因为并非所有Route节点都有routeId子节点。在这种情况下，s.Element("routeId")返回null，因此在尝试读取Value属性时会引发异常。一个方便的解决方法是将元素强制转换为string，而不是调用Value属性：

where (string)s.Element("routeId") == "1231"