通过 LINQ 嵌套组到嵌套对象

Question

我无法使用 LINQ 查询解决此问题。

所以我们有Book的表结构如下：

LibraryId || LibraryName || ShelveId || ShelveName || Cost || Name || ForeName || Stuff

我想先按图书馆分组，然后按书架分组。图书馆是书架的清单，书架是书的清单。性能很重要。这是真实数据的片段。

var table = new[] {
    new Book (1, "Green", 42, "A", 10, "Gra", "Bar", "etc."),
    new Book (1, "Green", 43, "B", 21, "Grb", "Bar", "etc."),
    new Book (2, "Blue", 652, "C", 10, "Blc", "Bar", "etc."),
    new Book (2, "Blue", 652, "C", 01, "Bl2", "Bar", "etc."),
    new Book (2, "Blue", 123, "D", 12, "Bld", "Bar", "etc."),
    new Book (8, "White", 94, "E", 14, "Foo", "Bar", "etc."),
    new Book (9, "Grey", 142, "F", 11, "Foo", "Bar", "etc."),
    new Book (9, "Grey", 142, "F", 12, "Bar", "Bar", "etc.")
};

类：

class Book
{
    public int LibraryId {get;set;}
    public string LibraryName {get;set;}

    public int ShelveId {get;set;}
    public string ShelveName {get;set;}

    public int Cost {get;set;}
    public string Name {get;set;}
    public string ForeName {get;set;}
    public string Stuff {get;set;}

    public Book(int libraryId, string libraryName, int shelveId, string shelveName
                , int cost, string name, string foreName, string stuff)
    {
        LibraryId = libraryId;
        LibraryName = libraryName;
        ShelveId = shelveId;
        ShelveName = shelveName;
        Cost = cost;
        Name = name;
        ForeName = foreName;
        Stuff = stuff;
    }
}

class Library
{
    public int Id {get;set;}
    public string Name {get;set;}
    public int Cost {get;set;}
    public List<Shelve> Shelves {get;set;}

    public Library (Shelve shelve)
    {
        Id = shelve.Books[0].LibraryId;
        Name = shelve.Books[0].LibraryName;
        Cost = shelve.Cost;
        Shelves = new List<Shelve> {shelve};
    }
}

class Shelve
{
    public int Id {get;set;}
    public string Name {get;set;}
    public int Cost {get;set;}
    public List<Book> Books {get;set;}

    public Shelve (Book book)
    {
        Id = book.ShelveId;
        Name = book.ShelveName;
        Cost = book.Cost;
        Books = new List<Book> {book};
    }
}

我用一个很好的老foreach来实现我的行为：

var libraries = new List<Library> { new Library (new Shelve(table[0])) };
foreach (var item in table.Skip(1))
{
    if (item.LibraryId != libraries.Last().Id)
    {
        libraries.Add(new Library(new Shelve(item)));
        continue;
    }

    if (item.ShelveId != libraries.Last().Shelves.Last().Id)
    {
        libraries.Last().Cost += item.Cost;
        libraries.Last().Shelves.Add(new Shelve(item));
        continue;
    }

    libraries.Last().Cost += item.Cost;
    libraries.Last().Shelves.Last().Cost += item.Cost;
    libraries.Last().Shelves.Last().Books.Add(item);
}
var total = libraries.Sum(x => x.Cost);

据我所知，这是一个 O(n) 的解决方案。

现在，我想重构它。我想我们可以用GroupBy 做点什么。我试过这个：

var grouped = table
    .GroupBy(l => new { l.ShelveId, l.LibraryId})
    .GroupBy(l => l.Key.LibraryId);

foreach(var country in grouped)
{
    foreach(var state in country)
    {
        foreach(var personInState in state)
        {
            Console.WriteLine(personInState.Name);
        }
    }
}

但我不知道如何汇总成本并将 LibraryName 和 ShelveName 添加到每个 Library 和 Shelve。

Try it Online!（带有基本测试）

Answer 1

也许您可以通过使用如下计算的属性来简化它

class Shelve
{
    public int Id {get;set;}
    public string Name {get;set;}
    public List<Book> Books {get;set;} = List<Book>();
    public int Cost 
    {
        get{ return this.Books.Sum(x => x.Cost); } 
    }
}

你可以对Library类做同样的事情......

class Library
{
    public int Id {get;set;}
    public string Name {get;set;}
    public List<Shelve> Shelves {get;set;} = new List<Shelve>();
    public int Cost 
    {
        get{ return this.Shelves.Sum(x => x.Cost); } 
    }
}

我认为它可以使您的业务逻辑代码更加清晰，并且您无需使用复杂的 group by 表达式来敲头