Question

我需要帮助使用具有特定where条件的LINQ读取xml元素。

我需要为一个县找到max air_temp 即县名=“布恩”和小时id =“06/03/2009 09：00CDT”

我尝试了类似下面的内容，但没有运气：

 Dim custs As IEnumerable = From c In Element.Load("C:\meridian.xml").Elements("county") _
                            Select c.Elements("hour").Elements("air_temp").Max()

 For Each x In custs
        Response.Write(custs(0).ToString())
 Next

-------------------这是xml文件：

 <forecasts>
      <issued>06/02/2009 12:00CDT</issued> 
    - <county name="Adair">
    - <hour id="06/02/2009 12:00CDT">
          <air_temp>61</air_temp> 
          <cloud_cover>overcast</cloud_cover> 
          <dew_point>59</dew_point> 
          <precip_prob>90</precip_prob> 
          <precip_rate>0.12</precip_rate> 
          <precip_type>rain</precip_type> 
          <snow_rate>0.0</snow_rate> 
          <wind_direction>NE</wind_direction> 
          <wind_speed>12</wind_speed> 
          <dew_point_confidence>-3/+3</dew_point_confidence> 
          <road_temp>64</road_temp> 
          <road_frost_prob>0</road_frost_prob> 
          <road_potential_evap_rate>429</road_potential_evap_rate> 
          <road_temp_confidence>-3/+2</road_temp_confidence> 
          <dew_point_confidence>-3/+3</dew_point_confidence> 
          <bridge_temp>63</bridge_temp> 
          <bridge_temp_confidence>-4/+2</bridge_temp_confidence> 
          <bridge_frost>NO</bridge_frost> 
      </hour>
    - <hour id="06/02/2009 13:00CDT">
          <air_temp>61</air_temp> 
          <cloud_cover>overcast</cloud_cover> 
          <dew_point>60</dew_point> 
          <precip_prob>70</precip_prob> 
          <precip_rate>0.01</precip_rate> 
          <precip_type>rain</precip_type> 
          <snow_rate>0.0</snow_rate> 
          <wind_direction>ENE</wind_direction> 
          <wind_speed>10</wind_speed> 
          <dew_point_confidence>-3/+3</dew_point_confidence> 
          <road_temp>65</road_temp> 
          <road_frost_prob>0</road_frost_prob> 
          <road_potential_evap_rate>411</road_potential_evap_rate> 
          <road_temp_confidence>-3/+2</road_temp_confidence> 
          <dew_point_confidence>-3/+3</dew_point_confidence> 
          <bridge_temp>64</bridge_temp> 
          <bridge_temp_confidence>-4/+1</bridge_temp_confidence> 
          <bridge_frost>NO</bridge_frost> 
      </hour>

Answer 1

Dim document = XDocument.Load("meridian.xml")
Dim air_temps = From county In document.Root.Elements("county") _
                From hour in county.Elements("hour") _
                From air_temp in hour.Elements("air_temp") _
                Select CInt(air_temp)
Dim max_air_temp = air_temps.Max()

使用XML文字：

Dim forecasts = XElement.Load("meridian.xml")
Dim air_temps = From air_temp In forecasts.<county>.<hour>.<air_temp> _
                Select CInt(air_temp)
Dim max_air_temp = air_temps.Max()

Answer 2

我假设你需要“country / max temp.date / max temp.value”聚合作为输出。如果是这样，这将解决问题：

Dim meridian = XDocument.Load("meridian.xml")
Dim maxByCounty = _
    From county In meridian.<forecasts>.<county> _
    Let maxHour = (From hour In county.<hour> _
                   Order By CType(hour.<air_temp>, Integer) Desescending _
                  ).First _
    Select New With { .Name = county.<name>, _
                      .Hour = maxHour.@id, 
                      .AirTemp = maxHour.<air_temp> }

然后你可以使用这样的结果：

For Each m In maxByCounty
    Console.WriteLine(m.Name, m.Hour, m.AirTemp)
Next

Answer 3

不应该是

From hour In county.Elements("hour") Where hour.Attribute("id")...

而不是

From hour In county.Elements("hour") Where county.Element("hour").Attribute("id")...

此外，您不应将回复发布到其他帖子作为额外答案。

阅读XML元素＆amp;在Vb.net中使用LINQ的子节点 - 帮助我在哪里条件:(

3 个答案: