如何列出用户及其评论

Question

我在列出用户及其评论时遇到了困难。我有一个 Sampledata（我需要的所有数据都存放在那里），我必须使用 LINQ 并以 XML 格式打印它，如下所示： https://i.stack.imgur.com/LMZZ7.png

这是 SampleData（评论所在的部分很重要）：

static public Publisher[] Publishers =
    {
      new Publisher {Name="FunBooks"},
      new Publisher {Name="Joe Publishing"},
      new Publisher {Name="I Publisher"}
    };

    static public Author[] Authors =
    {
      new Author {FirstName="Johnny", LastName="Good"},
      new Author {FirstName="Graziella", LastName="Simplegame"},
      new Author {FirstName="Octavio", LastName="Prince"},
      new Author {FirstName="Jeremy", LastName="Legrand"}
    };

    static public Subject[] Subjects =
    {
      new Subject {Name="Software development",Description="developing and others"},
      new Subject {Name="Novel",Description="great feelings"},
      new Subject {Name="Science fiction",Description="out of space and everywhere"}
    };

    static public Book[] Books =
    {
      new Book {                                        // [0]
        Title="Funny Stories",
        Publisher=Publishers[0],
        Authors=new[]{Authors[0], Authors[1]},
        PageCount=101,
        Price=25.55M,
        PublicationDate=new DateTime(2004, 11, 10),
        Isbn="0-000-77777-2",
        Subject=Subjects[0]
      },
      new Book {                                        // [1]
        Title="LINQ rules",
        Publisher=Publishers[1],
        Authors=new[]{Authors[2]},
        PageCount=300,
        Price=12M,
        PublicationDate=new DateTime(2007, 9, 2),
        Isbn="0-111-77777-2",
        Subject=Subjects[0]
      },
      new Book {                                        // [2]
        Title="C# on Rails",
        Publisher=Publishers[1],
        Authors=new[]{Authors[2]},
        PageCount=256,
        Price=35.5M,
        PublicationDate=new DateTime(2007, 4, 1),
        Isbn="0-222-77777-2",
        Subject=Subjects[0]
      },
      new Book {                                        // [3]
        Title="All your base are belong to us",
        Publisher=Publishers[1],
        Authors=new[]{Authors[3]},
        PageCount=1205,
        Price=35.5M,
        PublicationDate=new DateTime(2006, 5, 5),
        Isbn="0-333-77777-2",
        Subject=Subjects[2]
      },
      new Book {                                        // [4]
        Title="Bonjour mon Amour",
        Publisher=Publishers[0],
        Authors=new[]{Authors[1], Authors[2]},
        PageCount=50,
        Price=29M,
        PublicationDate=new DateTime(1973, 2, 18),
        Isbn="2-444-77777-2",
        Subject=Subjects[1]
      }
    };

    static public User[] Users = 
    {
        new User{Name="Fred"},
        new User{Name="Barney"},
        new User{Name="Wilma"}
    };

    static public Review[] Reviews =
    {
        new Review{ Book = Books[0], Comments="cc1", Rating=2, User=Users[0]},
        new Review{ Book = Books[0], Comments="cc2", Rating=3, User=Users[2]},
        new Review{ Book = Books[1], Comments="cc3", Rating=1, User=Users[0]},
        new Review{ Book = Books[1], Comments="cc4", Rating=2, User=Users[1]},
        new Review{ Book = Books[1], Comments="cc5", Rating=1, User=Users[2]},
        new Review{ Book = Books[2], Comments="cc6", Rating=3, User=Users[2]},        
        new Review{ Book = Books[3], Comments="cc7", Rating=4, User=Users[2]},
        new Review{ Book = Books[4], Comments="cc8", Rating=5, User=Users[1]}
    };

    static SampleData()
    {
        // Books -- Reviews haben einnen Doppelverweise
        //          daher kann erst hier  Book-->Review gesetzt werden
        Books[0].Reviews = new[] { Reviews[0], Reviews[1] };
        Books[1].Reviews = new[] { Reviews[2], Reviews[3], Reviews[4] };
        Books[2].Reviews = new[] { Reviews[5] };
        Books[3].Reviews = new[] { Reviews[6] };
        Books[4].Reviews = new[] { Reviews[7] };
    }

这是我目前写的：

IEnumerable<XElement> xElements =
                from review in SampleData.Reviews
                select
                    new XElement("Benutzer",
                        new XElement("User", new XAttribute("Name", "Barney")),
                 new XElement("Review",  (from review2 in SampleData.Reviews select review2.Comments).ToList().First())
                 );
            var customersXml = new XElement("UserReviews", xElements);
            Console.WriteLine(customersXml);

这是输出： https://i.stack.imgur.com/SqY7P.png

问题是有几个输出而不是一个输出（我只制作了第一部分而不是整个 XML 输出）。 有没有更好的方法来实现这一点？

Answer 1

在循环评论之前只创建一次 Benutzer 元素。
按用户名对评论进行分组，以将它们组合在一个用户元素下。

var element = new XElement(,
    "Benutzer",
    sampleData.Reviews
        .GroupBy(r => r.User.Name)
        .Select(g => new XElement(
            "User", 
            new XAttribute("Name", g.Key),
            g.Select(r => new XElement("Review", r.Comments))
        )
);