"Include" 在 Entity Framework Core 中 SelectMany + Select 之后不工作

Question

我使用 Entity Framework Core (v2) 进行了此查询，但 Include/ThenInclude 无法按预期工作。这是查询：

 var titlesOwnedByUser = context.Users
                   .Where(u => u.UserId == userId)
                   .SelectMany(u => u.OwnedBooks)
                   .Select(b => b.TitleInformation)
                   .Include(ti => ti.Title)
                   .ThenInclude(n => n.Translations);

查询有效，但我得到的标题的标题设置为 null。

澄清一下，类是这些

class User 
{
     public int Id { get; set; }
     public List<BookUser> OwnedBooks { get; set; }
}

class Book 
{
    public int Id { get; set; }
    public TitleInformation TitleInformation { get; set; }
    public List<BookUser> Owners { get; set; }
}

class BookUser 
{
     public int BookId { get; set; }
     public int UserId { get; set; }
     public Book Book { get; set; }
     public User User { get; set; }
}

class MyContext
{
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
        modelBuilder.Entity<BookUser>()
            .HasOne(x => x.User)
            .WithMany(x => x.OwnedBooks)
            .HasForeignKey(x => x.UserId);

        modelBuilder.Entity<BookUser>()
            .HasOne(x => x.Book)
            .WithMany(x => x.Owners)
            .HasForeignKey(x => x.BookId);
     }
}

class TitleInformation
{
    public int Id { get; set; }
    public Title Title { get; set; }
    public Title Subtitle { get; set; }
}

class Title
{
     public int Id { get; set; }
     public string OriginalTitle { get; set; }
     public List<Translation> Translations { get; set; }
}

我需要做什么才能使返回的可查询中的翻译加载？

Answer 1

这是 Loading Related Data - Ignored includes 中描述的当前 EF Core 限制：

If you change the query so that it no longer returns instances of the entity type that the query began with, then the include operators are ignored.

据此，您需要从context.Set<TitleInformation>()开始查询。但是为了产生所需的过滤，您需要从 TitleInformation 到 Book 的反向导航属性，您的模型目前缺少该导航：

class TitleInformation
{
    // ...
    public Book Book { get; set; } // add this and map it properly with fluent API
}

一旦你有了它，你就可以使用这样的东西：

var titlesOwnedByUser = context.Set<TitleInformation>()
    .Include(ti => ti.Title)
        .ThenInclude(n => n.Translations)
    .Where(ti => ti.Book.Owners.Any(bu => bu.UserId == userId));

或者，如果TitleInformation和Book之间的关系是一对多的（上面是一对一的）：

class TitleInformation
{
    // ...
    public List<Book> Books { get; set; }
}

分别为：

var titlesOwnedByUser = context.Set<TitleInformation>()
    .Include(ti => ti.Title)
        .ThenInclude(n => n.Translations)
    .Where(ti => ti.Books.SelectMany(b => b.Owners).Any(bu => bu.UserId == userId));

"Include" 在 Entity Framework Core 中 SelectMany + Select 之后不工作

"Include" not working after SelectMany + Select in Entity Framework Core

c#

entity-framework

entity-framework-core

iqueryable