c# - LINQ to XML - 如何正确使用 XDocument

Question

现在我要开始说这确实是一个任务。然而，在遇到 Linq to XML 语法之前，我几乎完成了它。

我有 2 个类:轨道和 CD 现在作为作业的一部分，我创建了一张 CD，然后向其中添加了一些轨道。在搜索了很多完美解释了如何从 xml 到对象的教程之后，我似乎无法正常工作(对象到 xml)。

我目前有:

//My list of cds
List<CD> cds = new List<CD>();
//Make a new CD and add some tracks to it
CD c1 = new CD("Awake","Dream Theater");
Track t1 = new Track("6:00", "Dream Theater", new TimeSpan(00, 05, 31));
Track t2 = new Track("Caught in a Web", "Dream Theater", new TimeSpan(00, 05, 28));
Track t3 = new Track("Innocence Faded", "Dream Theater", new TimeSpan(00, 05, 34));
c1.addTrack(t1);
c1.addTrack(t2);
c1.addTrack(t3);
cds.Add(c1);

//Make another cd and add it
CD c2 = new CD("Second cd","TestArtist");
Track t4 = new Track("TrackForSecond","TestArtist",new TimeSpan(00,13,37));
c2.addTrack(t4);
cds.add(c2);

现在这就是让我获得需要放入 XML 的对象的原因。 XML 部分是:

XDocument xmlOutput = new XDocument (
     new XDeclaration("1.0","utf-8","yes"),
     (from cl in cds orderby cl.getArtist()
        select new XElement("cd",  /*From new to the end of this is the error*/
            (
               from c in cds
                   select new XAttribute("artist",c.getArtist())
            ),
            (
               from c in cds
                   select new XAttribute("name", c.getTitle())
            ),
            new XElement("tracks",
               (
                   from t in c1.getTracks()
                       select new XElement("track",
                           new XElement("artist",t1.getArtist()),    
                           new XElement("title",t1.getTitle()),
                           new XElement("length",t1.getLength())
                       )          
               )                    
            )
        )
    )                   
);
Console.WriteLine(xmlOutput);

这非常有效(让我得到我需要的结果!)只需 1 张 cd。当我决定添加另一张 CD 时，它显示:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Xml.Linq.dll
Duplicate Attribute (cd)

它指向 XDocument。除了这个不起作用之外，它感觉很愚蠢(来自 cds x2 中的 c)但无论我尝试什么，我似乎都无法阻止这种语法讨厌我:

(
from c in cds
   select new XAttribute("artist",c.getArtist()),    
   select new XAttribute("name", c.getTitle()) //No not happening!
),

如果您能提供任何帮助，我们将非常高兴!

Answer 1

首先，我建议您对方法使用属性和 C# 风格的命名。以下是如何重构您的类:

public class CD
{
    private readonly List<Track> _tracks = new List<Track>();

    public CD(string artist, string title)
    {
        Artist = artist;
        Title = title;
    }

    public string Artist { get; private set; }
    public string Title { get; private set; }

    public  IEnumerable<Track> Tracks
    {
        get { return _tracks; }
    } 

    public void AddTrack(Track track)
    {
        _tracks.Add(track);
    }

    public CD WithTrack(string title, TimeSpan length)
    {
        AddTrack(new Track(Artist, title, length));
        return this;
    }
}

这是 Value Object class - 私有(private) setter 不允许更改此类之外的属性值。这是轨道类:

public class Track
{
    public Track(string artist, string title, TimeSpan length)
    {
        Artist = artist;
        Title = title;
        Length = length;
    }

    public string Artist { get; set; }
    public string Title { get; private set; }
    public TimeSpan Length { get; private set; }
}

现在您可以使用 Fluent API创建 CD 集合:

List<CD> cds = new List<CD>
    {
        new CD("Awake", "Dream Theater")
            .WithTrack("6:00", new TimeSpan(00, 05, 31))
            .WithTrack("Caught in a Web", new TimeSpan(00, 05, 28))
            .WithTrack("Innocence Faded", new TimeSpan(00, 05, 34)),
        new CD("Second cd", "TestArtist")
            .WithTrack("TrackForSecond", new TimeSpan(00, 13, 37))
    };

这是 XML 创建:

var xDoc = new XDocument(
    new XDeclaration("1.0", "utf-8", "yes"),
    new XElement("cds",
          from cd in cds
          orderby cd.Artist
          select new XElement("cd",
               new XAttribute("artist", cd.Artist),
               new XAttribute("name", cd.Title),
               from t in cd.Tracks
               select new XElement("track",
                     new XElement("artist", t.Artist),
                     new XElement("title", t.Title),
                     new XElement("length", t.Length)));

您在这里遇到了几个问题 - 缺少根节点，并在每次迭代中枚举所有 CD。