LINQ to XML 的简单应用

1. 创建XML文档

static void Main(string[] args)
    {
      CreateMusicLibrary();
    }

    static void CreateMusicLibrary()
    {
      XDocument musicLibrary =
        new XDocument(
          new XDeclaration("1.0","utf-8","yes"),//new XProcessingInstruction("xml-stylesheet","href='music.xslt'"),new XComment("This document holds details of my music collection"),new XElement("musicLibrary",CreateCDElement("1","Parallel Lines",2001,"Blondie","New Wave"),CreateCDElement("2","Bat Out of Hell","Meatloaf","Rock"),CreateCDElement("3","Abbey Road",1987,"The Beatles",CreateCDElement("4","The Dark Side of the Moon",1994,"Pink Floyd",CreateCDElement("5","Thriller","Michael Jackson","Pop")));
      Console.WriteLine(musicLibrary.ToString());    //使用ToString方法显示XML文档时会忽略文档中的声明
      Console.ReadLine();
    }

    static XElement CreateCDElement(string id,string title,int year,string artist,string genre)
    {
      return new XElement("cd",new XAttribute("id",id),new XElement("title",title),new XElement("year",year),new XElement("artist",artist),new XElement("genre",genre));
    }

1.1 创建带名称空间的文档，并把名称空间声明为默认名称空间：

static void CreateMusicLibrary()
    {
      XNamespace ns = "http://www.wrox.com/namespaces/apps/musicLibrary";   //使用XNamespace类声明命名空间，并将其应用到元素和属性上
      XElement musicLibrary =
        new XElement(ns + "musicLibrary",CreateCDElement(ns,"1","2","3","4","5","Pop"));
      Console.WriteLine(musicLibrary.ToString());
      Console.ReadLine();
    }

    static XElement CreateCDElement(XNamespace ns,string id,string genre)
    {
      return new XElement(ns + "cd",new XElement(ns + "title",new XElement(ns + "year",new XElement(ns + "artist",new XElement(ns + "genre",genre));
    }

1.2 创建带有前缀名的名称空间文档

  static void Main(string[] args)
    {
      CreateMusicLibrary();
    }

    static void CreateMusicLibrary()
    {
      XNamespace ns = "http://www.wrox.com/namespaces/apps/musicLibrary";
      XElement musicLibrary =
        new XElement(ns + "musicLibrary",new XAttribute(XNamespace.Xmlns + "ns",ns.NamespaceName),//使用XAttribute类将命名空间URI映射到前缀名上
          CreateCDElement(ns,genre));
    }

2. 从XML 文档中提取数据

需要查询的xml文档如下：

<?xml version="1.0" encoding="utf-8"?>
<musicLibrary>
  <cd id="1">
    <title>Parallel Lines</title>
    <year>2001</year>
    <artist>Blondie</artist>
    <genre>New Wave</genre>
  </cd>
  <cd id="2">
    <title>Bat Out of Hell</title>
    <year>2001</year>
    <artist>Meatloaf</artist>
    <genre>Rock</genre>
  </cd>
  <cd id="3">
    <title>Abbey Road</title>
    <year>1987</year>
    <artist>The Beatles</artist>
    <genre>Rock</genre>
  </cd>
  <cd id="4">
    <title>The Dark Side of the Moon</title>
    <year>1994</year>
    <artist>Pink Floyd</artist>
    <genre>Rock</genre>
  </cd>
  <cd id="5">
    <title>Thriller</title>
    <year>2001</year>
    <artist>Michael Jackson</artist>
    <genre>Pop</genre>
  </cd>
</musicLibrary>

 static void Main(string[] args)
    {
      XElement musicLibrary = XElement.Load(@"MusicLibrary.xml");
      Console.WriteLine("All Titlesn==========");
      ShowTitles(musicLibrary);
      Console.WriteLine("nTitles before CD 3n==================");
      ShowTitlesBefore(musicLibrary);
      Console.WriteLine("nTitles after CD 3n=================");
      ShowTitlesAfter(musicLibrary);
      Console.WriteLine("nTitles by Genren===============");
      GroupOnGenre(musicLibrary);
      Console.ReadLine();
    }

    static void ShowTitles(XElement musicLibrary)
    {
      foreach (XElement t in musicLibrary.Elements("cd").Elements("title"))
      // alternative using Descendants method.
      // foreach (XElement t in musicLibrary.Descendants("title"))
      {
        Console.WriteLine(t.Value);
      }
    }

    static void ShowTitlesBefore(XElement musicLibrary)
    {
      XElement cd3 = (from cd in musicLibrary.Elements("cd")
                      where cd.Attribute("id").Value == "3"
                      select cd).FirstOrDefault();
      foreach (XElement t in cd3.ElementsBeforeSelf("cd").Elements("title"))
      {
        Console.WriteLine(t.Value);
      }
    }

    static void ShowTitlesAfter(XElement musicLibrary)
    {
      XElement cd3 = musicLibrary.Elements("cd").Where(cd => cd.Attribute("id").Value == "3").FirstOrDefault();
      foreach (XElement t in cd3.ElementsAfterSelf("cd").Elements("title"))
      {
        Console.WriteLine(t.Value);
      }
    }

    static void GroupOnGenre(XElement musicLibrary)
    {
      var groupQuery = from cd in musicLibrary.Elements("cd")
                        group cd by cd.Element("genre").Value into genreGroup
                        orderby genreGroup.Key
                        select new
                        {
                          Genre = genreGroup.Key,Titles = from title in genreGroup.Elements("title")
                                  select title.Value
                        };
      foreach (var entry in groupQuery)
      {
        Console.WriteLine("Genre: {0}",entry.Genre);
        Console.WriteLine("----------------");
        foreach (var title in entry.Titles)
        {
          Console.WriteLine("t{0}",title);
        }
        Console.WriteLine();
      }
    }

3. 修改XML文档

 static void Main(string[] args)
    {
      XElement musicLibrary = XElement.Load(@"MusicLibrary.xml");
      Console.WriteLine("Adding a New CDn===============");
      AddNewCD(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.WriteLine("nRemoving a CD=============");
      RemoveCD(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.WriteLine("nAdding a New CD Directlyn========================");
      AddNewCDDirectly(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.WriteLine("nUpdate Year with ReplaceNodesn=============================");
      UpdateYearWithReplaceNodes(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.WriteLine("nUpdate Year with SetElementValue================================");
      UpdateYearWithSetElementValue(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.WriteLine("nUpdate Attribute Value====================");
      UpdateAttributeValue(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.WriteLine("nReplace CD Content==================");
      ReplaceCD(musicLibrary);
      Console.WriteLine(musicLibrary);
      Console.ReadLine();
    }

    static void AddNewCD(XElement musicLibrary)
    {
      XElement cd = CreateCDElement("6","Back in Black",2003,"AC/DC","Rock");
      musicLibrary.Add(cd);
    }

    static void AddNewCDDirectly(XElement musicLibrary)
    {
      musicLibrary.Add(
          new XElement("cd",6),"Back in Black"),2003),"AC/DC"),"Rock")));
    }

    static void RemoveCD(XElement musicLibrary)
    {
      XElement cd = (from entry in musicLibrary.Elements("cd")
                     where entry.Attribute("id").Value == "6"
                     select entry).FirstOrDefault();
      if (null != cd)
      {
        cd.Remove();
      }
    }

    static XElement CreateCDElement(string id,genre));
    }

    static void UpdateYearWithReplaceNodes(XElement musicLibrary)
    {
      XElement cd = (from entry in musicLibrary.Elements("cd")
                     where entry.Attribute("id").Value == "3"
                     select entry).FirstOrDefault();
      cd.Element("year").ReplaceNodes("1986");
    }

    static void UpdateYearWithSetElementValue(XElement musicLibrary)
    {
      XElement cd = (from entry in musicLibrary.Elements("cd")
                     where entry.Attribute("id").Value == "3"
                     select entry).FirstOrDefault();
      cd.SetElementValue("year","1987");
    }

    static void UpdateAttributeValue(XElement musicLibrary)
    {
      XElement cd = (from entry in musicLibrary.Elements("cd")
                     where entry.Attribute("id").Value == "3"
                     select entry).FirstOrDefault();
      cd.SetAttributeValue("id","7");
    }

    static void ReplaceCD(XElement musicLibrary)
    {
      XElement cd = (from entry in musicLibrary.Elements("cd")
                      where entry.Attribute("id").Value == "1"
                      select entry).FirstOrDefault();

      cd.ReplaceWith( new XElement("cd",1),"Rock")));
    }

（编辑：李大同）

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