如何訪問 Authors 中的值？

Question

好吧，我必須列出作者的書和他們的評論數量，我必須在 LINQ 的幫助下以 XML 格式寫出來。

這是數據（只有書籍、作者和評論所在的部分很重要）

static public class SampleData
  {
    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] };
    }

  }

這是我寫的（我只能打印作者）

var elements2 = new XElement("Autoren", SampleData.Authors
                .GroupBy(g => (g.FirstName + " " + g.LastName))
                .Select(g => new XElement("Autor", new XAttribute("Name", g.Key)))
                );

            var xml2 = new XElement("AuthorReviews", elements2);
            Console.WriteLine(xml2);

它應該看起來像這樣：[1]： https://i.stack.imgur.com/pQS2q.png

一般來說，我的問題是，我實際上只能打印作者（如果我使用SampleData.Authors ），但是當我想使用SampleData.Books時，我不知道如何訪問 Authors 中的值（它所在的部分“new[]{Authors[..]}”讓我很困惑）。

Answer 1

嘗試以下操作：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;


namespace ConsoleApplication176
{
    class Program
    {

        static void Main(string[] args)
        {

            XElement autoren = new XElement("Autoren");

            foreach (Author author in SampleData.Authors)
            {
                string fullName = author.FirstName + " " + author.LastName;
                XElement autor = new XElement("Author", new XAttribute("Name", fullName));
                autoren.Add(autor);
                foreach(Book book in SampleData.Books.Where(x => x.Authors.Any(y => y.FirstName + " " + y.LastName == fullName)))
                {
                    XElement xBook = new XElement("Buch", new object[] {new XAttribute("Title", book.Title), new XAttribute("Anzreviews", book.Reviews.Average(x => x.Rating))});
                    autor.Add(xBook);
                }
            }
  
        }
    }
    public class Publisher
    {
        public string Name { get; set; }
    }
    public class Author
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
    public class Subject
    {
        public string Name { get; set; }
        public string Description { get; set; }
    }
    public class Book
    {
        public string Title { get; set; }
        public Publisher Publisher { get; set; }
        public Author[] Authors { get; set; }
        public int PageCount { get; set; }
        public decimal  Price { get; set; }
        public DateTime PublicationDate { get; set; }
        public string Isbn { get; set; }
        public Subject Subject { get; set; }
        public Review[] Reviews { get; set; }
    }
    public class User
    {
        public string Name { get; set; }
    }
    public class Review
    {
        public Book Book { get;set;}
        public string Comments {get;set;}
        public int Rating { get;set;}
        public User User { get;set;}
    }

    static public class SampleData
    {
        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] };
        }

    }

  
}

Answer 2

你有多么不尋常的數據庫布局！

在你用這個創建嚴肅的軟件之前，考慮創建主鍵和外鍵，並實現正確的一對多表關系和多對多表關系。

如果您不知道我在說什么，請向您的項目負責人請教一些基本的數據庫想法。 它會在未來得到回報。

因此，您有一系列Books ，每Book都有一個或多個Authors ，並且每本書都有零多個評論。 作者已經在您的圖書中，但您決定將評論放在單獨的表格中

我必須列出作者及其書籍和評論數量

還沒寫過書的作者還是作者嗎？ 還是您只想要至少寫過一本書的作者？ 您的書籍列表中是否有作者不在您的作者列表中？ 您的作者列表中的作者是唯一的，還是您有幾個不同的作者具有相同的名字和姓氏？

將原來的“書有作者”變成“作者有書”並不難

我不確定“他們的評論數量”。 你是指這些作者對他們所有書籍的評論數量，還是他們每本書的評論數量？ 你只想要評論的數量，而不是評分嗎？

通常，如果您有帶有零個或多個子項的項目，例如教師和學生，並且您想要反轉這一點，因此學生和他們的教師，您使用 SelectMany 將教師和學生扁平化為一名教師和一名學生的組合，然后 GroupBy Student 讓學生和他們的老師在一起。

所以首先我們將“Books with their Authors”扁平化為 [Book, Author] 組合，然后我們 groupby Author：

var result = books.SelectMany(book => book.Author)

輸入：

• 本書 A 與作者 1, 2
• 書 B 與作者 3
• 與作者 1、3 一起預訂 C

在 SelectMany 之后：[A, 1], [A, 2], [B, 3], [C,1], [C, 3]

繼續 LINQ：GroupBy 作者：

.GroupBy(authorBookCombination => authorBookCombination.Author,

    // parameter resultSelector: take every Author, with all his Books, to create one new
    (author, booksOfThisAuthor) => new 
    {
        // Select only the Author properties that you want to save
        FirstName = author.FirstName,
        LastName = author.LastName,

        Books = booksOfThisAuthor.Select(book => new
        {
            // select only the Book properties that you want to save:
            Title = book.Title,
            Comments = book.Comments,
            ... // etc

            // don't Add the Authors!
            // TODO: "amount" of Reviews
        }

這是最簡單的部分：讓作者帶着他們的書。 如果您還想要還沒有寫任何東西的作者，請從作者表開始，為每個作者找到他的零個或多個書：

var result = Authors.Select(author => new
{
    FirstName = author.FirstName,
    LastName = author.LastName,

    Books = Books.Where(book => book.Author.Any(bookAuthor => bootkAuthor == author))
    .Select(book => new
    {
        Title = book.Title,
        ...
        // TODO reviews
    })
    .ToList(),
})

用文字表示：從 Authors 表中的每個 Author 中，獲取他的名字和姓氏。 從這些書中獲取至少有一個作者等於該作者的所有書籍，以及 select 幾個屬性。

現在要獲取每本書的評論數量，請輸入我寫 TODO 的 Select：

ReviewAmount = reviews.Where(review => review.Book == book).Count(),

簡而言之：對於我們為這位作者拍攝的每一本書，請查看表格或評論。 每一篇評論都是關於一本書。 只保留與我們正在創建的書相同的書的那些評論。

如果您想要的不僅僅是數量或評論：

ReviewInformation = reviews.Where(review => review.Book == book)
     .Select(review => new
     {
         Rating = review.Rating,
         Comments = review.Comments,
     })
     .ToList(),

請注意，ReviewInformation.Count 是您最初要求的評論數量。

結果是一系列作者，每個作者都有他的零或多本書，每本書都有（數量）其零或更多評論。

現在您已經有了這個，您可以使用 XMLSerializer 將其序列化為 XML。