概要
本文提供一个EF Core的优化案例，主要介绍一些EF Core常用的优化方法，以及在优化过程中，出现性能反复的时候的解决方法，并澄清一些对优化概念的误解，例如AsNoTracking并不包治百病。
本文使用的是Dotnet 6.0和EF Core 7.0。
代码及实现
背景介绍
本文主要使用一个图书和作者的案例，用于介绍优化过程。
- 一个作者Author有多本自己写的的图书Book
- 一本图书Book有一个发行商Publisher
- 一个作者Author是一个系统用户User
- 一个系统用户User有多个角色Role
本实例中Author表和Book数据量较大，记录数量全部过万条，其它数据表记录大概都是几十或几百条。具体实体类定义请见附录。
查询需求
我们需要查找写书最多的前两名作家，该作家需要年龄在20岁以上，国籍是法国。需要他们的FirstName， LastName， Email，UserName以及在1900年以前他们发行的图书信息，包括书名Name和发行日期Published。
基本优化思路
本人做EF Core的复杂查询优化，并不推荐直接查看生成的SQL代码，我习惯按照如下方式进行：
首先，进行EF的LINQ代码检查（初筛），找到明显的错误。
- 查看代码中是否有基本错误，主要针对全表载入的问题。例如EF需要每一步的LINQ扩展方法的返回值都是IQueryable类型，不能有IEnumerable类型；
- 查看是否有不需要的栏位；
- 根据情况决定是否加AsNoTracking，注意这个东西有时候加了也没用；
其次，找到数据量较大的表，进行代码整理和针对大数据表的优化（精细化调整）
- 在操作大数据表时候，先要进行基本的过滤；
- 投影操作Select应该放到排序操作后面；
- 减少返回值数量，推荐进行分页操作；
本人推荐一旦出现性能反复的时候或者代码整体基本完成的时候，再去查看生成的SQL代码。
初始查询代码
public List<AuthorWeb> GetAuthors() {
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
.Include(x => x.User)
.ThenInclude(x => x.UserRoles)
.ThenInclude(x => x.Role)
.Include(x => x.Books)
.ThenInclude(x => x.Publisher)
.ToList()
.Select(x => new AuthorWeb
{
UserCreated = x.User.Created,
UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
UserId = x.User.Id,
RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
Id = y.Id,
Name = y.Name,
Published = y.Published,
ISBN = y.ISBN,
PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
AuthorNickName = x.NickName,
Id = x.Id
})
.ToList()
.Where(x => x.AuthorCountry == "France" && x.AuthorAge == 20)
.ToList();
var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().Take(2).ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in orderedAuthors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
Benchmark测试后，系统资源使用情况如下：
代码性能非常差，内存消耗很大，一次执行就要消耗190MB，执行时间超过2s。如果是放到WebAPI里面调用，用户会有明显的卡顿感觉；如果面临高并发的情况，很可得会造成服务器资源紧张，返回各种500错误。
优化代码
初筛
按照我们的优化思路，在查看上面的代码后，发现一个严重的问题。
虽然每次LINQ查询返回都是IQueryable类型，但是源码中有多个ToList()，尤其是第一个，它的意思是将Author， Book，User，Role，Publisher等多个数据表的数据全部载入，前面已经说了，Author， Book两张表的数据量很大，必然影响性能。
我们需要删除前面多余的ToList()，只保留最后的即可。请参考附录中的方法GetAuthors_RemoveToList()。
在GetAuthors_RemoveToList()基础上，对照用户的需求，发现查询结果中包含了Role相关的信息和很多Id信息，但是查询结果并不需要这些，因此必须删掉。请参考附录中的方法GetAuthorsOptimized_RemoveColumn()
在GetAuthorsOptimized_RemoveColumn的基础上，我们再加入AsNoTracking方法。请参考附录中的方法GetAuthorsOptimized_AsNoTracking()
我们在Benchmark中，测试上面提到的三个方法，直接结果如下：
从Benchmark的测试结果上看，删除多余ToList方法和删除多余的栏位，确实带来了性能的大幅提升。
但是增加AsNoTracking，性能提反而下降了一点。这也说明了AsNoTracking并不是适用所有场景。Select投影操作生成的AuthorWeb对像，并不是EF管理的，与DbContext无关，它只是作为前端API的返回值。相当于EF做了没有用的事，所以性能略有下降。
代码进一步调整
初筛阶段完成后，下面对代码进一步整理
下面Take和Order操作可以并入基本的查询中，Take可以帮助我们减少返回值的数量。请见 GetAuthorsOptimized_ChangeOrder()方法。
var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().Take(2).ToList();
在GetAuthorsOptimized_ChangeOrder基础上，对于dbContext.Authors，Author是一张数据量很大的表，我们需要在其进行联表操作前，先过滤掉不需要的内容，所以我们可以把Where前提，还有就是将排序操作放到投影的Select前面完成。请见 GetAuthorsOptimized_ChangeOrder方法。
上面的两个优化方法的执行结果如下：
可以看到性略能有提升。
下面我们为了进一步提升性能，可以查看一下生成的SQL代码，看看是否还有优化的空间。
GetAuthorsOptimized_ChangeOrder方法生成的SQL如下：
SELECT [u].[FirstName], [u].[LastName], [u].[Email], [u].[UserName], [t].[
BooksCount], [t].[Id], [u].[Id], [b].[Name], [b].[Published], [b].[Id], [t].[Age
], [t].[Country]
FROM (
SELECT TOP(@__p_0) [a].[Id], [a].[Age], [a].[BooksCount], [a].[Country
], [a].[UserId]
FROM [Authors] AS [a]
WHERE [a].[Country] = N'France' AND [a].[Age] >= 20
ORDER BY [a].[BooksCount] DESC
) AS [t]
INNER JOIN [Users] AS [u] ON [t].[UserId] = [u].[Id]
LEFT JOIN [Books] AS [b] ON [t].[Id] = [b].[AuthorId]
ORDER BY [t].[BooksCount] DESC, [t].[Id], [u].[Id]
从生成SQL来看，Author表在使用之前过滤掉了相关的内容，但是直接Left Join了[Books]这个大表。我们可以按照前面提到的1900年以前的查询要求，在左联之前先过滤一下，请参考 GetAuthorsOptimized_SelectFilter方法。
该方法执行后，生成的SQL如下：
SELECT [u].[FirstName], [u].[LastName], [u].[Email], [u].[UserName], [t].[
BooksCount], [t].[Id], [u].[Id], [t0].[Name], [t0].[Published], [t0].[Id], [t].[
Age], [t].[Country]
FROM (
SELECT TOP(@__p_1) [a].[Id], [a].[Age], [a].[BooksCount], [a].[Country
], [a].[UserId]
FROM [Authors] AS [a]
WHERE [a].[Country] = N'France' AND [a].[Age] >= 20
ORDER BY [a].[BooksCount] DESC
) AS [t]
INNER JOIN [Users] AS [u] ON [t].[UserId] = [u].[Id]
LEFT JOIN (
SELECT [b].[Name], [b].[Published], [b].[Id], [b].[AuthorId]
FROM [Books] AS [b]
WHERE [b].[Published] < @__date_0
) AS [t0] ON [t].[Id] = [t0].[AuthorId]
ORDER BY [t].[BooksCount] DESC, [t].[Id], [u].[Id]
在左联之前，确实进行了过滤，该方法的性能测试如下：
在避免Book表直接进行左联后，性能有所提升。
最后一个优化点，是在EF Core 5.0里面提供了带Filter功能的Include方法，也可以用于本案例的优化，但是该特性但是存在一些局限性，具体请参考EF Core中带过滤器参数的Include方法
但是此方法又涉及了将IQueryable转换成IEnumerable的操作，最后要将生成的Author对象全部转换成AuthorWeb对象。代码过于繁琐，而且带来的性能提升也不明显。因此放弃这个点。
dbContext.Authors
.AsNoTracking()
.Include(x => x.Books.Where(b => b.Published < date))
......
结论
从这个优化过程来看，其实对性能提升最大的贡献就是删除多余的ToList()，避免全表载入和删除不需要的栏位两项。其它所谓更精细的优化，性能提升有限。
附录
实体类定义
public class Author
{
public int Id { get; set; }
public int Age { get; set; }
public string Country { get; set; }
public int BooksCount { get; set; }
public string NickName { get; set; }
[ForeignKey("UserId")]
public User User { get; set; }
public int UserId { get; set; }
public virtual List<Book> Books { get; set; } = new List<Book>();
}
public class Book
{
public int Id { get; set; }
public string Name { get; set; }
[ForeignKey("AuthorId")]
public Author Author { get; set; }
public int AuthorId { get; set; }
public DateTime Published { get; set; }
public string ISBN { get; set; }
[ForeignKey("PublisherId")]
public Publisher Publisher { get; set; }
public int PublisherId { get; set; }
}
public class Publisher
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime Established { get; set; }
}
public class User
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string UserName { get; set; }
public string Email { get; set; }
public virtual List<UserRole> UserRoles { get; set; } = new List<UserRole>();
public DateTime Created { get; set; }
public bool EmailConfirmed { get; set; }
public DateTime LastActivity { get; set; }
}
public class Role
{
public int Id { get; set; }
public virtual List<UserRole> UserRoles { get; set; } = new List<UserRole>();
public string Name { get; set; }
}
public class AuthorWeb
{
public DateTime UserCreated { get; set; }
public bool UserEmailConfirmed { get; set; }
public string UserFirstName { get; set; }
public DateTime UserLastActivity { get; set; }
public string UserLastName { get; set; }
public string UserEmail { get; set; }
public string UserName { get; set; }
public int UserId { get; set; }
public int AuthorId { get; set; }
public int Id { get; set; }
public int RoleId { get; set; }
public int BooksCount { get; set; }
public List<BookWeb> AllBooks { get; set; }
public int AuthorAge { get; set; }
public string AuthorCountry { get; set; }
public string AuthorNickName { get; set; }
}
public class BookWeb
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime Published { get; set; }
public int PublishedYear { get; set; }
public string PublisherName { get; set; }
public string ISBN { get; set; }
}
优化方法
[Benchmark]
public List<AuthorWeb> GetAuthors() {
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
.Include(x => x.User)
.ThenInclude(x => x.UserRoles)
.ThenInclude(x => x.Role)
.Include(x => x.Books)
.ThenInclude(x => x.Publisher)
.ToList()
.Select(x => new AuthorWeb
{
UserCreated = x.User.Created,
UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
UserId = x.User.Id,
RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
Id = y.Id,
Name = y.Name,
Published = y.Published,
ISBN = y.ISBN,
PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
AuthorNickName = x.NickName,
Id = x.Id
})
.ToList()
.Where(x => x.AuthorCountry == "France" && x.AuthorAge >= 20)
.ToList();
var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().Take(2).ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in orderedAuthors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
[Benchmark]
public List<AuthorWeb> GetAuthors_RemoveToList()
{
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
.Include(x => x.User)
.ThenInclude(x => x.UserRoles)
.ThenInclude(x => x.Role)
.Include(x => x.Books)
.ThenInclude(x => x.Publisher)
// .ToList()
.Select(x => new AuthorWeb
{
UserCreated = x.User.Created,
UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
UserId = x.User.Id,
RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
Id = y.Id,
Name = y.Name,
Published = y.Published,
ISBN = y.ISBN,
PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
AuthorNickName = x.NickName,
Id = x.Id
})
// .ToList()
.Where(x => x.AuthorCountry == "France" && x.AuthorAge >=20)
.ToList();
var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().Take(2).ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in orderedAuthors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
[Benchmark]
public List<AuthorWeb> GetAuthorsOptimized_RemoveColumn()
{
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
// .Include(x => x.User)
//.ThenInclude(x => x.UserRoles)
// .ThenInclude(x => x.Role)
// .Include(x => x.Books)
// .ThenInclude(x => x.Publisher)
.Select(x => new AuthorWeb
{
// UserCreated = x.User.Created,
// UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
// UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
// UserId = x.User.Id,
// RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
// Id = y.Id,
Name = y.Name,
Published = y.Published,
// ISBN = y.ISBN,
// PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
AuthorNickName = x.NickName,
// Id = x.Id
})
.Where(x => x.AuthorCountry == "France" && x.AuthorAge >=20)
.ToList();
var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().Take(2).ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in orderedAuthors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
[Benchmark]
public List<AuthorWeb> GetAuthorsOptimized_AsNoTracking()
{
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
.AsNoTracking()
// .Include(x => x.User)
// .ThenInclude(x => x.UserRoles)
// .ThenInclude(x => x.Role)
// .Include(x => x.Books)
// .ThenInclude(x => x.Publisher)
.Select(x => new AuthorWeb
{
//UserCreated = x.User.Created,
// UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
// UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
// UserId = x.User.Id,
//RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
// Id = y.Id,
Name = y.Name,
Published = y.Published,
//ISBN = y.ISBN,
//PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
//AuthorNickName = x.NickName,
Id = x.Id
})
.Where(x => x.AuthorCountry == "France" && x.AuthorAge >=20)
.ToList();
var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in authors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
[Benchmark]
public List<AuthorWeb> GetAuthorsOptimized_Take_Order()
{
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
.AsNoTracking()
.Select(x => new AuthorWeb
{
UserFirstName = x.User.FirstName,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
Name = y.Name,
Published = y.Published,
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
AuthorNickName = x.NickName,
})
.Where(x => x.AuthorCountry == "France" && x.AuthorAge >=20)
.OrderByDescending(x => x.BooksCount)
.Take(2)
.ToList();
// var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in authors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
[Benchmark]
public List<AuthorWeb> GetAuthorsOptimized_ChangeOrder()
{
using var dbContext = new AppDbContext();
var authors = dbContext.Authors
.AsNoTracking()
.Where(x => x.Country == "France" && x.Age >=20)
.OrderByDescending(x => x.BooksCount)
// .Include(x => x.User)
// .ThenInclude(x => x.UserRoles)
// .ThenInclude(x => x.Role)
// .Include(x => x.Books)
// .ThenInclude(x => x.Publisher)
.Select(x => new AuthorWeb
{
//UserCreated = x.User.Created,
// UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
// UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
// UserId = x.User.Id,
//RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books.Select(y => new BookWeb
{
// Id = y.Id,
Name = y.Name,
Published = y.Published,
//ISBN = y.ISBN,
//PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
//AuthorNickName = x.NickName,
Id = x.Id
})
.Take(2)
.ToList();
// var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().ToList();
List<AuthorWeb> finalAuthors = new List<AuthorWeb>();
foreach (var author in authors)
{
List<BookWeb> books = new List<BookWeb>();
var allBooks = author.AllBooks;
foreach (var book in allBooks)
{
if (book.Published.Year < 1900)
{
book.PublishedYear = book.Published.Year;
books.Add(book);
}
}
author.AllBooks = books;
finalAuthors.Add(author);
}
return finalAuthors;
}
// [Benchmark]
public List<AuthorWeb> GetAuthorsOptimized_IncludeFilter()
{
using var dbContext = new AppDbContext();
var date = new DateTime(1900, 1, 1);
var authors = dbContext.Authors
.AsNoTracking()
.Include(x => x.Books.Where(b => b.Published < date))
.Include(x => x.User)
// .IncludeFilter(x =>x.Books.Where(b =>b.Published.Year < 1900))
.Where(x => x.Country == "France" && x.Age >=20)
.OrderByDescending(x => x.BooksCount)
// .ThenInclude(x => x.UserRoles)
// .ThenInclude(x => x.Role)
// .Include(x => x.Books)
// .ThenInclude(x => x.Publisher)
.Take(2)
.ToList();
// var orderedAuthors = authors.OrderByDescending(x => x.BooksCount).ToList().ToList();
var authorList = authors.AsEnumerable().Select(x => new AuthorWeb
{
//UserCreated = x.User.Created,
// UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
// UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
// UserId = x.User.Id,
//RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books
// .Where(b => b.Published < date)
.Select(y => new BookWeb
{
// Id = y.Id,
Name = y.Name,
Published = y.Published,
//ISBN = y.ISBN,
//PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
//AuthorNickName = x.NickName,
// Id = x.Id
}).ToList();
return authorList;
}
[Benchmark]
public List<AuthorWeb> GetAuthorsOptimized_SelectFilter()
{
using var dbContext = new AppDbContext();
var date = new DateTime(1900, 1, 1);
var authors = dbContext.Authors
.AsNoTracking()
.Include(x => x.Books.Where(b => b.Published < date))
.Where(x => x.Country == "France" && x.Age >=20)
.OrderByDescending(x => x.BooksCount)
.Select(x => new AuthorWeb
{
//UserCreated = x.User.Created,
// UserEmailConfirmed = x.User.EmailConfirmed,
UserFirstName = x.User.FirstName,
// UserLastActivity = x.User.LastActivity,
UserLastName = x.User.LastName,
UserEmail = x.User.Email,
UserName = x.User.UserName,
// UserId = x.User.Id,
//RoleId = x.User.UserRoles.FirstOrDefault(y => y.UserId == x.UserId).RoleId,
BooksCount = x.BooksCount,
AllBooks = x.Books
.Where(b => b.Published < date)
.Select(y => new BookWeb
{
// Id = y.Id,
Name = y.Name,
Published = y.Published,
//ISBN = y.ISBN,
//PublisherName = y.Publisher.Name
}).ToList(),
AuthorAge = x.Age,
AuthorCountry = x.Country,
//AuthorNickName = x.NickName,
// Id = x.Id
})
.Take(2)
.ToList();
return authors;
}
