Verwendung der Where-Klausel, um DateTime-Bedingung zu entsprechen

Question

Die folgende Abfrage funktioniert gut für mich, bis ich Where Bedingung für Hour mit Attribut Id = '06/02/2009 12:00CDT' gilt.

Ich brauche die maximale Temperatur nur für das heutige Datum, und ich bin nicht in der Lage, die Where Bedingung im Datumsfeld zu verwenden. Irgendwelche Ideen, was ich falsch mache?

Dim document = XDocument.Load("c:\meridian.xml") 
Dim wind_gusts = From county In document.Root.Elements("county") Where county.Attribute("name") = "Adams" _ 
From hour In county.Elements("hour") Where county.Element("hour").Attribute("id").Value = "06/02/2009 13:00CDT" _ 
From wind_gust In hour.Elements("wind_gust") _ 
Select CInt(wind_gust) '< DateTime.Parse("06/03/2009") _ 
'DateTime.Parse(county.Element("hour" + ID).Attribute("id")) 
'Dim wind_gust_value = wind_gusts.Max() 

For Each m In wind_gusts 
    Response.Write(m.ToString()) 
Next 

Unten ist die xml:

<?xml version="1.0" ?> 
- <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> 
+ <hour id="06/02/2009 14:00CDT"> 
    <air_temp>64</air_temp> 
    <cloud_cover>overcast</cloud_cover> 
    <dew_point>60</dew_point> 
    <precip_prob>60</precip_prob> 
    <precip_rate>trace</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>65</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>560</road_potential_evap_rate> 
    <road_temp_confidence>-3/+2</road_temp_confidence> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <bridge_temp>65</bridge_temp> 
    <bridge_temp_confidence>-3/+2</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 15:00CDT"> 
    <air_temp>63</air_temp> 
    <cloud_cover>overcast</cloud_cover> 
    <dew_point>59</dew_point> 
    <precip_prob>50</precip_prob> 
    <precip_rate>trace</precip_rate> 
    <precip_type>rain</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>NE</wind_direction> 
    <wind_gust>15</wind_gust> 
    <wind_speed>12</wind_speed> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <road_temp>63</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>397</road_potential_evap_rate> 
    <road_temp_confidence>-4/+3</road_temp_confidence> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <bridge_temp>63</bridge_temp> 
    <bridge_temp_confidence>-3/+2</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 16:00CDT"> 
    <air_temp>64</air_temp> 
    <cloud_cover>overcast</cloud_cover> 
    <dew_point>57</dew_point> 
    <precip_prob>40</precip_prob> 
    <precip_rate>trace</precip_rate> 
    <precip_type>rain</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>ENE</wind_direction> 
    <wind_gust>16</wind_gust> 
    <wind_speed>11</wind_speed> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <road_temp>62</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>400</road_potential_evap_rate> 
    <road_temp_confidence>-3/+3</road_temp_confidence> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <bridge_temp>61</bridge_temp> 
    <bridge_temp_confidence>-4/+2</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 17:00CDT"> 
    <air_temp>63</air_temp> 
    <cloud_cover>overcast</cloud_cover> 
    <dew_point>56</dew_point> 
    <precip_prob>30</precip_prob> 
    <precip_rate>trace</precip_rate> 
    <precip_type>rain</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>ENE</wind_direction> 
    <wind_gust>15</wind_gust> 
    <wind_speed>10</wind_speed> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <road_temp>61</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>344</road_potential_evap_rate> 
    <road_temp_confidence>-3/+3</road_temp_confidence> 
    <dew_point_confidence>-3/+3</dew_point_confidence> 
    <bridge_temp>60</bridge_temp> 
    <bridge_temp_confidence>-4/+2</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 18:00CDT"> 
    <air_temp>62</air_temp> 
    <cloud_cover>mostly cloudy</cloud_cover> 
    <dew_point>54</dew_point> 
    <precip_prob>20</precip_prob> 
    <precip_rate>trace</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/+4</dew_point_confidence> 
    <road_temp>61</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>530</road_potential_evap_rate> 
    <road_temp_confidence>-3/+3</road_temp_confidence> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <bridge_temp>61</bridge_temp> 
    <bridge_temp_confidence>-3/+2</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 19:00CDT"> 
    <air_temp>61</air_temp> 
    <cloud_cover>mostly cloudy</cloud_cover> 
    <dew_point>52</dew_point> 
    <precip_prob>10</precip_prob> 
    <precip_rate>trace</precip_rate> 
    <precip_type>rain</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>ENE</wind_direction> 
    <wind_speed>7</wind_speed> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <road_temp>68</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>959</road_potential_evap_rate> 
    <road_temp_confidence>-3/+3</road_temp_confidence> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <bridge_temp>66</bridge_temp> 
    <bridge_temp_confidence>-3/+3</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 20:00CDT"> 
    <air_temp>60</air_temp> 
    <cloud_cover>mostly cloudy</cloud_cover> 
    <dew_point>51</dew_point> 
    <precip_prob>10</precip_prob> 
    <precip_rate>trace</precip_rate> 
    <precip_type>rain</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>ENE</wind_direction> 
    <wind_speed>5</wind_speed> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <road_temp>65</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>495</road_potential_evap_rate> 
    <road_temp_confidence>-3/+4</road_temp_confidence> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <bridge_temp>62</bridge_temp> 
    <bridge_temp_confidence>-3/+3</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 21:00CDT"> 
    <air_temp>57</air_temp> 
    <cloud_cover>mostly cloudy</cloud_cover> 
    <dew_point>51</dew_point> 
    <precip_prob>0</precip_prob> 
    <precip_rate>0.00</precip_rate> 
    <precip_type>none</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>NE</wind_direction> 
    <wind_speed>5</wind_speed> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <road_temp>62</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>339</road_potential_evap_rate> 
    <road_temp_confidence>-3/+4</road_temp_confidence> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <bridge_temp>59</bridge_temp> 
    <bridge_temp_confidence>-3/+3</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 
+ <hour id="06/02/2009 22:00CDT"> 
    <air_temp>56</air_temp> 
    <cloud_cover>mostly cloudy</cloud_cover> 
    <dew_point>51</dew_point> 
    <precip_prob>0</precip_prob> 
    <precip_rate>0.00</precip_rate> 
    <precip_type>none</precip_type> 
    <snow_rate>0.0</snow_rate> 
    <wind_direction>ENE</wind_direction> 
    <wind_speed>5</wind_speed> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <road_temp>60</road_temp> 
    <road_frost_prob>0</road_frost_prob> 
    <road_potential_evap_rate>309</road_potential_evap_rate> 
    <road_temp_confidence>-3/+4</road_temp_confidence> 
    <dew_point_confidence>-3/+4</dew_point_confidence> 
    <bridge_temp>58</bridge_temp> 
    <bridge_temp_confidence>-3/+3</bridge_temp_confidence> 
    <bridge_frost>NO</bridge_frost> 
    </hour> 

Answer 1

Paar Dinge:

1. ich keine Elemente für die Grafschaft = "Adams" gesehen haben. Das Dokument, das Sie gaben, hatte county = "Adair".

2. Ich denke, Sie versuchen, eine CInt() für eine Zeichenfolge, die wie <wind_gust>15</wind_gust> aussieht.

3. Es gibt kein <wind_gust> Element für County Adair und 12: 00CDT. Also habe ich am 15: 00CDT abgefragt, was mir ein wind_gust-Element beschert hat. Wenn Sie eine Zeit abfragen, die kein wind_gust-Element enthält, erhalten Sie die leere Menge.

4. Sie sagten, Sie wollten Max Temp, aber Sie sind tatsächlich für wind_gust Abfrage. Ich sehe keine Elemente namens max_temp.

Dieser Code funktioniert für mich:

Public Sub QueryWindGust(ByVal county As String, ByVal hour As String) 
    Dim document = XDocument.Load("meridian.xml") 
    Dim selection = From c In document.Root.Elements("county") _ 
     Where c.Attribute("name").Value = "Adair" _ 
     From h In c.Elements("hour") _ 
     Where h.Attribute("id").Value = hour _ 
     From g In h.Elements("wind_gust") _ 
     Select CInt(g.Value) 


    Console.WriteLine("For county {0}, hour ({1}):", county, hour) 
    If (selection.Count > 0) 
     Console.Write("wind gust: ") 
     For Each m In selection 
      Console.WriteLine(m.ToString() & ": (" & m.GetType().ToString() & ")") 
     Next 
    Else 
     Console.WriteLine("No elements returned.") 
    End If 
End Sub 

Public Sub Run() 
    QueryWindGust("Adams","06/02/2009 12:00CDT") 
    QueryWindGust("Adair","06/02/2009 12:00CDT") 
    QueryWindGust("Adair","06/02/2009 15:00CDT") 
End Sub