Question

我有一个图书数据库，其中包含作者的ICollection。我想使用LINQ根据AuthorId返回作者对象。

Book db

int BookId
string Name { get; set; }
public ICollection<Author> Authors { get; set; }

Author db
int AuthorId
string Name
ICollection<Quote> Quotes { get; set; }
ICollection<Penname> Pennames { get; set; } - Edit: Added for clarity

我尝试过：

var test = _context.Book.Include(x => x.Authors).Include("Authors.Quotes")
                    .Select(y => y.Authors)

哪个给了我

EntityQueryable<ICollection<Authors>>
[0] {HashSet<Author>} [0]{Author} [1]{Author} [3]{Author} 
[1] {HashSet<Author>} [0]{Author} [1]{Author} 
[2] {HashSet<Author>} [0]{Author} [1]{Author}

我只是不知道如何遍历Authors列表中的Authors。类似于以下内容：

var id = 2

var test = _context.Book.Include(x => x.Authors).Include("Authors.Quotes")
                    .Select(y => y.Authors.Select(x => x.Author).Where(x => x.AuthorId == id))

如果我进行了重大更新，我可能会使用弹性...

更新@Marko Papic：

谢谢。奇怪的是，如果我使用下面的方法来获取作者的书籍清单，则会得到我所期望的报价和笔名清单

var test = _context.Book.Include(x => x.Authors)
                   .ThenInclude(x => x.Quotes)
                   .Include(x => x.Authors)
                   .ThenInclude(x => x.Pennames)

但是，如果我使用SelectMany，则引号和笔名最终将为空

var test = _context.Book.Include(x => x.Authors)
                   .ThenInclude(x => x.Quotes)
                   .Include(x => x.Authors)
                   .ThenInclude(x => x.Pennames)
                   .SelectMany(x => x.Authors).Where(x => x.AuthorId == id);

Author myauthor
int AuthorId = 2
string Name = "Bob"
ICollection<Quote> Quotes = null
ICollection<Penname> Pennames = null

Answer 1

您可以使用SelectMany：

var test = _context.Book.Include(x => x.Authors).ThenInclude(x => x.Quotes)
                    .SelectMany(x => x.Authors).Where(x => x.AuthorId == id);

Answer 2

我认为包含将被忽略，因为从documentation开始，查询的结果类型与您启动时的dbset类型不同：

如果您更改查询以使其不再返回的实例，查询开始的实体类型，则包含运算符为忽略。

我假设bool和Books之间的关系是多对多的，如果是这种情况，那么我将按照以下方式进行查询：

Authors

复杂的LINQ查询-多个表关系

2 个答案: